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Chemistry Y10 Flashcards

1
Q

Define atom

A

A minuscule particle which makes up all matter

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2
Q

Define element

A

A chemical substance which is made up of only one type of atom and is found in the periodic table

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3
Q

How are groups determined in the periodic table?

A

Each group contains elements with similar properties

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4
Q

Define mixture

A

Two or more different elements which are mixed together but do not chemically react

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5
Q

Define compound

A

A substance made from two or more atoms of different elements which have been chemically bonded together. The atoms of each are in fixed proportions throughout

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6
Q

How do you separate water, sand and salt?

A

Pour the mixture through filter paper in a funnel which leaves sand residue, then heat the leftover filtrate to obtain salt crystals

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7
Q

Define immiscible

A

Two solids or two liquids which do not mix completely

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8
Q

Define miscible

A

Two substances which are mixable

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9
Q

How to separate an immiscible substance?

A

Add the mixture into the top of a cone shaped separating funnel with a hemispherical end but keep the stop clock at the bottom closed, close the funnel then shake gently by inverting the funnel several times, carefully open the tap to release excess vapour pressure, open the top and bottom which allows the lower phase to be released then the upper layer is removed through the top

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10
Q

Which two particles are found in the nucleus of an atom?

A

Protons and neutrons

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11
Q

Define mass number

A

The sum of the number of protons and neutrons

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12
Q

Define atomic number

A

Number of protons which is the same as the number of electrons

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13
Q

What are the charges of each particle?

A

Proton is positive, electron is negative, neutron is neutral

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14
Q

Define isotope

A

An atom of the same electron with a different number of neutrons but the same number of protons and electrons

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15
Q

Why does an atom have no overall charge?

A

There is an equal number of protons and electrons but protons have a positive charge and electrons have a negative therefore they cancel out

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16
Q

Mass of both a proton and a neutron?

A

1

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17
Q

Why are elements in group 0 unreactive?

A

They have full outer shells

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18
Q

What does the group number determine?

A

How many electrons are on the outer shell

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19
Q

What is the name for the group of elements with full outer shells?

A

Noble gases

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20
Q

What happens when metals lose electrons?

A

They form positive ions because there are more positive protons left than negative electrons

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21
Q

What happens when non metals gain electrons?

A

They form negative ions because there are more negative electrons than positive protons left

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22
Q

Define covalent bond

A

When non metals join together and share electrons in order to have a full shell. Forms a molecule

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23
Q

Define reactant

A

A substance which takes part and undergoes change in a reaction

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24
Q

Define product

A

The result of a reaction

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25
Q

Define aqueous solution

A

Solid dissolved in water

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26
Q

How is the modern periodic table arranged?

A

In order of increasing atomic number

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27
Q

Explain the process of distillation

A

Place the solution in a conical flask on a tripod over a Bunsen burner, this heats it up so the liquid with the lowest boiling point evaporates first, this will rise into the condenser where condensation occurs and the liquid will run into a collecting flask

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28
Q

Define diatomic molecule

A

Two atoms forming a molecule by sharing electrons

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29
Q

How do group 1 metals react with chlorine?

A

Vigorously to form metal chlorides

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30
Q

What happens with reactions as you go down the group?

A

Become increasingly violent

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31
Q

How do you test for hydrogen?

A

Place a lighted spill inside a test tube containing the gas and if hydrogen is present you will hear a squeaky pop

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32
Q

Name 3 properties of the group 1 metals

A

Low melting points, react with oxygen, soft

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33
Q

Why do atoms become more reactive as you descend down a group of metals?

A

They have more outer shells which means the outer shell electron is further away from the nucleus and more shielded by the shells and their attraction is weaker and this makes it easier for this outer electron to be lost

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34
Q

Why are smaller non metal atoms more reactive?

A

The outer electron is closer to the nucleus as their are less shells providing a shield and this makes it easier to attract another electron

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35
Q

Define oxidation

A

Loss of electrons

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36
Q

Define reduction

A

Gain of electrons

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37
Q

What do high grade ores contain

A

A high percentage of metal

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38
Q

Define ores

A

Rocks that contain enough metal to make is economical to extract

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39
Q

Define ionic bond

A

A chemical link between two atoms caused by the electrostatic force between oppositely charged ions in an ionic compound

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40
Q

Why is copper important in our technological society?

A

Used to make electrical wiring

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41
Q

How is sulphuric acid used to extract copper?

A

Produces copper sulphate solution which copper can be extracted from

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42
Q

Define smelting

A

The process of heating a copper ore to a high temperature in a furnace with air to produce impure copper

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43
Q

Name a advantage to extracting metals using bacteria rather than traditional methods?

A

More economical

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44
Q

Where does pure copper collect in electrolysis?

A

The negative electrode where they gain electrons to make ions

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45
Q

Define phytomining

A

The process of using plants to extract copper from low grade ores. Plants absorb copper through their roots and are burned to produce copper rich ash, copper is leached from this using sulphuric acid then is displaced using scrap iron or electrolysis

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46
Q

Define bio leaching

A

Using bacteria to extract copper from ores by breaking copper sulphur bonds, a very slow process

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47
Q

Define hydrocarbons

A

Compounds which contain the elements hydrogen carbon only

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48
Q

Define alkanes

A

Saturated hydrocarbons (have only have single bonds between carbon atoms)

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49
Q

Name 2 reasons copper should not be disposed of in landfill sites

A

Copper compounds are toxic, it can pollute the water and air and soil

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50
Q

Why are copper ores extracted from ores containing a low percentage of copper compounds?

A

Copper ores are running out, there are small amounts of high grade copper ores left

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51
Q

Why is it difficult to dispose of waste rock?

A

It takes up a lot of space

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52
Q

Why is the extraction of pure copper expensive?

A

Low percentage of copper in ores require a lot of rock to be moved and processed

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53
Q

What happens to viscosity and boiling point as a carbon chain increases and why?

A

They increase because the alkane becomes thicker, harder to pour and ignite as their flammability increases

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54
Q

Why are longer molecules more difficult to separate?

A

They have stronger forces between them so more energy is needed

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55
Q

Describe 5 steps of fractional distillation

A

Crude oil is put into a flask with a fractionating column (filled with glass rods) on top then is heated. Hydrocarbon chains of different lengths cool and condense at different heights due to their different boiling points. The liquid with the lowest boiling point evaporates first- when the temperature on the thermometer matches the boiling point of this liquid it will reach the top of the column. Liquids with higher boiling points may start to evaporate but the column is cooler towards the top so they will condense and run back down towards the flask. When the first liquid has been collected you raise temperature

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56
Q

Define fuel

A

Something that can be burned to release heat and light energy

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57
Q

Define combustion

A

The chemical reaction of a substance when it reacts with oxygen

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58
Q

How does the apparatus in combustion show water is produced?

A

Blue cobalt chloride paper turns pink

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59
Q

How does the apparatus in combustion show that carbon dioxide is produced?

A

Limewater turns cloudy

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60
Q

What colour does water turn white copper sulphate?

A

Blue

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61
Q

What happens when there is less oxygen than carbon?

A

Carbon does not react completely and the result is a colourless and poisonous gas carbon monoxide

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62
Q

Define alkene

A

Unsaturated hydrocarbons (contain double bonds between carbon atoms)

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63
Q

Why are long chain molecules broken down?

A

Long chains are in low demand so they are broken down into short chain which are more useful as fuels and in higher demand

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64
Q

Define thermal decomposition

A

The process of heating long chain hydrocarbons and passing them over a catalyst ,called cracking

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65
Q

How to test for alkenes and what is the result if present?

A

Use bromine water which will turn from orange to colourless

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66
Q

What type of reaction happens to petrol in a car engine?

A

Combustion

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67
Q

Why should sulphur be removed from petrol?

A

When it is burned sulphur dioxide is produced which causes acid rain

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68
Q

What happens when propane burns?

A

The propane reacts with oxygen which releases energy and produces carbon dioxide and water

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69
Q

Name the first four alkanes

A

Methane, ethane, propane, butane

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70
Q

Give 4 reasons why should steel cans be recycled

A

They are 100% recyclable, recycling one tonne of them saves 1.5 tonnes of iron ore, 0.5 tonnes of coal, 40% water usage

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71
Q

Why do ionic bonds have high melting points?

A

The oppositely charged ions are strongly attracted to each other by electrostatic force. Many strong bonds between ions takes a lot of energy to overcome

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72
Q

Why do ionic substances not conduct electricity when solid?

A

The ions are fixed and unable to move meaning they cannot allow energy to flow through

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73
Q

Why can ionic substances conduct energy when they are melted or dissolved in water?

A

The ions are free to move and therefore conduct electricity acting as charge carriers

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74
Q

What do ionic bonds create?

A

A giant ionic lattice with strong electrostatic forces of attraction between oppositely charged ions in all directions in the lattice

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75
Q

Why does aluminium oxide have such a high boiling point?

A

The ions formed have high charges therefore the attraction between the ions is very strong

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76
Q

Define small simple molecule

A

A molecule with a low melting and boiling point which cannot conduct electricity and only has weak attractive forces between the molecules so only a small amount of energy is needed to overcome them

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77
Q

Why are covalent compounds insulators?

A

They have no electric charge or free electrons to act as charge carriers

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78
Q

Why is diamond very hard?

A

The carbon atoms are held in place by strong covalent bonds in a very rigid giant molecular lattice. Each carbon atom forms FOUR covalent bonds

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79
Q

Why is graphite ideal as a lubricating material?

A

The carbon atoms are arranged in layers of hexagons. There are no covalent bonds between the layers which means they easily slide over each other. This makes graphite soft and slippery

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80
Q

Why is graphite a conductor of electricity?

A

It only uses three of its four outer shell electron to make three covalent bonds therefore it has one delocalised electron to carry charge

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81
Q

What are diamond and graphite referred to as?

A

The allotropes of carbon

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82
Q

Define malleable

A

Easily shaped

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83
Q

Define ductile

A

Can be drawn out into long thin wires

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84
Q

Define alloy

A

A mixture of metals

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85
Q

Why are alloys stronger and harder than pure metals?

A

They have a distorted structure which means their atoms are unable to move, strength increases

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86
Q

Define exothermic

A

A reaction where heat energy is given out to the surrounding and the reaction gets hot

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87
Q

Define endothermic

A

Heat energy is absorbed by the surroundings and the reaction gets cold

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88
Q

Explain Democritus theory about the atom

A

Around 400BC Democritus believed the universe was composed of two things: atoms and the void in which they exist and move. Atoms were tiny, uncuttable, solid particles surrounded by empty space and constantly moving at random

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89
Q

Explain JJ Thomson’s theory of the atom

A

In 1897 he proposed that the atom was composed of electrons surrounded by a medium of positive charge to cancel out the electrons negative charge

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90
Q

Explain the Rutherford gold foil experiment

A

In the early twentieth century, positively charged alpha particles were shot at a sheet of gold and a small amount of particles were deflected but a majority passed through the sheet, causing Rutherford to conclude that the mass of an atom was concentrated at its centre which was positively charged and there was a ‘cloud’ of negative electrons surrounding the nucleus

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91
Q

Explain Niels Bohr’s theory of the atom

A

In 1913 he realised that electrons should move around the nucleus but only in prescribed orbits (shells which are each a fixed distance from the nucleus) because if there was a cloud of negative electrons around the nucleus like Rutherford said, they would be attracted to the nucleus and cause the atom to collapse

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92
Q

Explain Lavoisiers periodic table

A

In 1789, he ordered the elements into four groups: gas-like elements, acid-making elements, metallic elements, earthy elements

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93
Q

Name 4 problems of Lavoisiers table

A

Contained elements and compounds, contained forms of energy, did not order elements in terms or atomic mass or number, cannot be used to work out electronic structures

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94
Q

Explain Newlands periodic table

A

In 1864, he established the law of octaves after realising that by ordering the elements according to increasing atomic weight, those with similar chemical and physical properties occur after each interval of seven elements

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95
Q

Name 3 problems with newlands tabke

A

Many elements in groups had dissimilar properties like copper and potassium, two elements in one place, no clear division between metals and non metals

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96
Q

Explain Mendeleevs table

A

In 1869, he realised that the chemical and physical properties of elements were related to their atomic mass in a periodic way therefore arranged elements so that groups with similar properties fell into vertical columns on his table, he predicted the discovery of other elements therefore left gaps

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97
Q

Explain the modern periodic table

A

Arranged in order of increasing atomic number, the group number determines how many electrons on the outer shell and the period determines how many shells they have

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98
Q

Define hydrated

A

Water of crystallisation

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99
Q

Define anhydrous

A

Without water

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100
Q

Define reversible reaction

A

One which can go in both directions

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101
Q

What do bond energy tables tell us?

A

The amount of energy needed to break a bond or the energy released when a bond is made

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102
Q

What is the equation for energy change

A

Energy in - energy out

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103
Q

In an exothermic reaction is the energy change positive or negative?

A

Negative because the energy released from forming new bonds is greater than the energy needed to break existing ones

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104
Q

In an endothermic reaction is the energy change positive or negative?

A

Positive because the energy needed to break bonds is greater than the energy released by new ones

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105
Q

Define rate

A

A measure of how fast or slow something happens

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106
Q

What is the equation for rate of reaction?

A

Amount of reactant used or amount of product formed divided by time

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107
Q

Define collision theory

A

Particles can only react when they collide with enough energy for a reaction to take place

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108
Q

What two factors does rate of reaction rely on?

A

Frequency of collisions between particles, energy with which particles collide

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109
Q

How do you work out rate on a graph?

A

Gradient of tangent to curve

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110
Q

What happens to the temperature of an acid as it is neutralised by an alkali?

A

It keeps increasing until the same amount of alkali has been added to the same amount of acid, then the temp decreases

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111
Q

What will happen to the rate of reaction when the concentration of acid is high?

A

There will be a high rate of reaction because there are more particles in a given volume and collisions take place more frequently

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112
Q

Give two reasons why you should do repeats in experiments

A

To identify an anomalous result, calculate a mean

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113
Q

Define reproducible

A

An investigation is repeated by another person or with different equipment and the same results are obtained

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114
Q

How do you calculate rate of reaction?

A

1divided by time taken

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115
Q

Why is the rate of reaction highest when the concentration of acid is high?

A

More particles in a given volume which means collisions take place more often

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116
Q

Why does the solution go cloudy in the reaction between sodium thiosulphate and hydrochloric acid?

A

Solid sulphur is made

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117
Q

Why is there a higher rate of reaction at a higher temperature?

A

Particles have more energy meaning they move faster and they are more likely to collide, the particles collide with more energy so the number of successful collisions increases and breaks activation energy barrier

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118
Q

What is the relationship between the size of the pieces of a solid material and it’s surface to volume ratio?

A

The smaller the size of pieces of solid material, the larger the surface area to volume ratio

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119
Q

What happens to surface area fo volume ratio when the side of a cube decrease by 10?

A

The surface area to volume ratio increases by 10

120
Q

What is the relationship between SA:V and rate of reaction?

A

The larger the SA:V, the quicker the reaction

121
Q

Define relative atomic mass

A

The average value for isotopes of that element

122
Q

Define relative formula mass

A

The sum of the relative atomic masses of the atoms in that formula

123
Q

How do you work out the percentage of an element in a formula?

A

Mass of element divided by relative formula mass, x 100

124
Q

Define redox reaction

A

A reversible reaction involving the transfer of electrons in which one reaction is an oxidation and the reverse is a reduction

125
Q

What is uncertainty?

A

Amount of error your measurements might have

126
Q

Equation for uncertainty

A

Range divided by 2

127
Q

How can you reduce uncertainty?

A

Measuring a greater amount of something

128
Q

Radius of an atom

A

0.1 nanometers (1x10^-10m)

129
Q

Equation for relative atomic mass

A

Sum of (isotope abundance x isotope mass number) divided by sum of abundances of all isotopes

130
Q

Why does a compound made from a metal and a non metal have such a high boiling point?

A

The compound consists of ions. The opposite charges (positive and negative) mean they are strongly attracted to eachother. This is called ionic bonding. They form a giant ionic lattice with strong attraction

131
Q

Equation for burning methane

A

methane + oxygen -> carbon dioxide + water

132
Q

When do you use filtration? 2 points

A

If your product is an insoluble solid that needs to be separated from a liquid reaction mixture, used in purification to separate out solid impurities in the reaction mixture

133
Q

Define soluble

A

Solid which can be dissolved

134
Q

Identify 2 ways to separate a soluble salt from a solution

A

Evaporation, crystallisation

135
Q

What is rock salt?

A

Mixture of sand (doesn’t dissolve in water) and salt (dissolves in water) which is spread onto roads in Winter

136
Q

Identify the four steps to separating a mixture containing an insoluble and a soluble solid (e.g rock salt)

A

Grind the mixture so salt crystals are small and will dissolve easily, put mixture in water and stir so salt dissolves (could heat mixture to help dissolve salt), filter mixture - grains of sand won’t fit through tiny holes in the paper but salt passes through as it’s part of the solution, evaporate the water so salt forms dry crystals

137
Q

Identify 4 steps to crystallisation

A

Pour solution in evaporating dish and gently heat so some solvent evaporates and solution will get more concentrated, when crystals start to form (point of crystallisation) remove the dish from heat and leave the solution to cool, salt should form crystals as it becomes insoluble in the cold highly concentrated solution, filter crystals out of the solution and leave them to dry or use a drying oven or dessicator

138
Q

When would you use crystallisation instead of evaporation?

A

When you want to make big crystals out of the salt

139
Q

How could you use distillation to produce pure water?

A

The water is heated, evaporates and is condensed and collected so eventually you are just left with salt in the flask

140
Q

What is the problem with simple distillation?

A

You can only use it to separate substances with very different boiling points. If the temperature goes higher than the boiling point of the substance with the higher boiling point, they will mix again.

141
Q

When do you use fractional distillation?

A

If you have a mixture of liquids with similar boiling points

142
Q

Why do you use distilled water in chemical experiments?

A

There are no impurities like ions in it which could interfere with results

143
Q

What did Rutherford expect to happen in the gold experiment due to the plum pudding model?

A

Expected particles to pass through the sheet or be slightly deflected at most because the positive charge of the atom was believed to be spread out through the ‘pudding’ of the atom however more were deflected than expected

144
Q

What particle did James Chadwick discover?

A

Neutron (a neutrally charged particle in the nucleus)

145
Q

How many elements are there?

A

Around 100

146
Q

What do the vertical columns (groups) of the periodic table show?

A

Elements with similar properties. How many electrons are on the outer shell

147
Q

How can you predict the properties of an element?

A

If you know the properties of another element in that group

148
Q

Why is it difficult for non metals to form positive ions by losing electrons?

A

Non metals are either to the right of the periodic table where they have lots of elements to lose to gain a full outer shell or they are towards the top which means there is strong attraction between the outer electrons and the nucleus due to less distance between them

149
Q

What causes metals to have similar properties and what are they?

A

Metallic bonding causes them to have similar properties: strong but malleable (can be bent or hammered into different shapes), great at conducting heat and electricity, high boiling and melting points. Delocalised electrons in metallic bonding produce all the properties

150
Q

Identify 5 properties of non metals

A

They don’t have metallic bonding so tend to be dull looking, more brittle, aren’t always solids at room temperature, don’t always conduct electricity, often have a lower density

151
Q

What are group 1 metals like?

A

Alkali metals - soft,, low density (first three in the group are les dense than water) silvery solids that can be stored in oil (and handled with forceps) as they are very reactive (they have one outer shell electron)

152
Q

What compounds do alkali metals usually form?

A

White solids which dissolve in water to form colourless solutions. Form a 1+ ion

153
Q

How do alkali metals react with water?

A

Vigorously to produce hydrogen gas and metal hydroxides (salts that dissolve in water to produce alkaline solutions) The more reactive an alkali metal is (further down the group), the more violent the reaction. Amount of energy given out by the reaction increases down the group

154
Q

How much energy is released when potassium reacts with water?

A

Enough to ignite hydrogen

155
Q

How do alkali metals react when heated in chlorine gas?

A

Vigorously to form white metal chloride salts. Reactivity increases as you go down the group so the reaction gets more vigorous

156
Q

How do alkali metals react with oxygen?

A

To form a metal oxide. Different types of metal oxide form depending on the metal. The metal tarnishes in the air (forms a dull metal oxide layer)

157
Q

Why are the group 1 elements called alkali metals?

A

They react with water to produce alkaline solutions

158
Q

What are the halogens?

A

Non metals with coloured vapours. Group 7 of periodic table

159
Q

What is fluorine?

A

Very reactive, poisonous yellow gas

160
Q

What is chlorine?

A

Fairly reactive, poisonous, dense green gas

161
Q

What is bromine?

A

Dense, poisonous, red-brown volatile liquid

162
Q

What is iodine?

A

Dark grey crystalline solid or purple vapour

163
Q

What do all halogens exist as?

A

Molecules (pairs of atoms) e.g Cl2

164
Q

What 3 things happen to halogens as you travel down the group?

A

Become less reactive, have higher relative atomic masses, have higher melting and boiling points

165
Q

Which 2 types of bonds do halogens form?

A

Share electrons via covalent bonding with other non metals -these compounds have simple molecular structures, form 1- ions called halides when they bond with metals -these compounds have ionic structures

166
Q

What are the noble gases?

A

Group 0 elements. Inert (don’t react much at all), non flammable, colourless gases at room temperature with full outer shells

167
Q

What do noble gases exist as?

A

Monatomic gases (single atoms not bonded to each other)

168
Q

What happens to boiling points as you go down Group 0 and why?

A

Increase because there is an increase in number of electrons in each atom leading to greater intermolecular forces between them which need to be overcome

169
Q

If neon is a gas at 25 degrees Celsius, what state is Helium at this temperature and why?

A

Helium is further up the group so has a lower boiling point meaning it is a gas at this temperature

170
Q

What is another phrase for a full outer shell?

A

Stable electronic structure

171
Q

What does the charge on the ion represent?

A

Number of electrons gained (-) or lost (+)

172
Q

What is the structure of sodium chloride?

A

Na+ and Cl- ions alternate, they form a closely packed regular ionic lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions in all directions in the lattice

173
Q

How do you work out empirical formula of a compound?

A

Balance the charges so the overall charge is zero. Or count up how many atoms there are of each element on a dot and cross diagram

174
Q

What happens when non metals bond together?

A

They form covalent bonds. Each covalent bond provides one extra shared electron for each atom

175
Q

Why are covalent bonds so strong?

A

Positively charged nuclei of bonded atoms are attracted to the shared pair of electrons by electrostatic forces.

176
Q

What can you use to show covalent bonding?

A

Dot and cross diagrams - electrons drawn in the overlap between the outer orbitals are shared between the two atoms

177
Q

What are two negatives of dot and cross diagrams?

A

Don’t show relative sizes of atoms, don’t show how the atoms are arranged in space

178
Q

What do 3D models of covalent bonds show? 3 things

A

Atoms, covalent bonds and their arrangement in space next to eachother however they do not show where the electrons in the bonds have come from

179
Q

How do you find molecular formula of a simple molecular compound?

A

Count up how many atoms there are of each element in a dot and cross diagram or 3D model

180
Q

Why does hydrogen exist as a molecule (2 atoms joined together as a covalent bond)?

A

It has just one electron so needs one more to complete the first shell so can form a single covalent bond with another hydrogen atom

181
Q

Why does chlorine exist as a molecule (2 atoms joined together as a covalent bond)?

A

Only needs one more outer electron so forms a single covalent bond with another chlorine atom

182
Q

Why does oxygen gas exist as a molecule (2 atoms joined together as a covalent bond)?

A

Needs two more electrons on its outer shell so forms a double covalent bond with another oxygen atom by sharing two pairs of electrons

183
Q

Why does nitrogen exist as a molecule (2 atoms joined together as a covalent bond)?

A

Needs three more electrons on its outer shell so forms a triple covalent bond with another nitrogen atom by sharing three pairs of electrons

184
Q

What type of bond do hydrogen and chlorine form and why?

A

Single covalent bond as they both need one more outer electron

185
Q

What type of bond does carbon form with hydrogen to make methane?

A

Carbon has 4 outer shell electrons (half a full shell) so forms four covalent bonds with hydrogen

186
Q

What is the formula for ammonia?

A

NH3

187
Q

What type of bond do hydrogen and oxygen form to make water?

A

Oxygen shares two pairs of electrons with two hydrogen atoms to form two single covalent bonds

188
Q

Why are melting and boiling points of simple molecular structures (containing covalent bonds) very low?

A

Forces between molecules are very weak. To boil or melt a compound, you only need to break these feeble intermolecular forces not the strong covalent bonds so the atoms are easily parted from each other. Therefore most molecular substances are gases or liquid at room temperature

189
Q

What happens as molecules (containing covalent bonds) get bigger?

A

Strength of intermolecular forces increases so more energy is needed to break them and melting and boiling points increase

190
Q

What are polymers?

A

Small units are linked together to form a long molecule with repeating sections - all atoms are joined together by covalent bonds

191
Q

What can you do instead of drawing out a long polymer molecule?

A

Draw out the repeating section and put it in brackets with n outside the brackets at the bottom. Draw bonds through the brackets to join up to the next repeating unit

192
Q

How do you find the molecular formula of a polymer?

A

Write down the molecular formula of the repeating unit in brackets then put n at the end outside of the bracket

193
Q

Why are polymers solid at room temperature?

A

Intermolecular forces between polymer molecules are larger than between simple covalent bonds so more energy is needed to break them. However intermolecular forces are still weaker than ionic bonds so they have lower boiling points than ionic or giant molecular compounds

194
Q

What are macromolecules?

A

Giant covalent structures in which all the atoms are bonded together by strong covalent bonds so they have high melting and boiling points. Don’t conduct electricity even when molten as they do not contain charged particles

195
Q

How is diamond arranged?

A

Each carbon atom forms four covalent bonds in a very rigid giant covalent structure

196
Q

Give 2 examples of macromolecules and state what they are both made up of

A

Diamond and graphite. Made of carbon atoms only and silicon dioxide (silica)

197
Q

How is graphite arranged?

A

Each carbon atom forms three covalent bonds to create layers of hexagons. Each carbon atom has one delocalised electron

198
Q

What is each grain of sand?

A

One giant structure of silicon and oxygen (silicon dioxide)

199
Q

Why do giant covalent structures like diamond, graphite, silicon have high melting and boiling points?

A

You have to break strong covalent bonds to melt or boil the structure

200
Q

Define allotrope

A

Different structural forms of the same element in the same physical state

201
Q

What is graphene?

A

One layer of graphite (a sheet of carbon atoms joined together in hexagons) The sheet is just one atom thick which makes it a two dimensional compound

202
Q

Why is graphene strong?

A

Due to the network of covalent bonds

203
Q

What can graphene be used for?

A

Can be added to composite materials to improve their strength without adding much weight as it is incredibly light

204
Q

Why does graphene have potential to be used in electronics?

A

Each carbon atom has one delocalised electron meaning it can conduct electricity throughout the whole structure

205
Q

Why are the properties of diamond, graphite and graphene different?

A

Their atoms are held together differently

206
Q

What are fullerenes?

A

Molecules of carbon shaped like closed tubes or hollow balls. Mainly made up of carbon atoms arranged in hexagons but can also contain pentagons and heptagons

207
Q

How could fullerenes be used to deliver a drug in the body?

A

They can be used to cage other molecules by forming a structure around it and trapping it inside

208
Q

How could fullerenes be used as industrial catalysts?

A

They have a huge surface area. Individual catalyst molecules could be attached to fullerenes (the bigger the surface area, the better)

209
Q

What do fullerenes work well as?

A

Lubricants

210
Q

What can fullerenes form?

A

Nanotubes (tiny carbon cylinders) Ratio between the length and diameter of nanotubes is very high. Nanotubes can conduct electricity and thermal energy and have a high tensile strength (don’t break while they’re stretched)

211
Q

What can nanotubes be used for? 3 things

A

Technology that uses very small particles is called nanotechnology, used in electronics, used to strengthen materials without adding too much weight such as in tennis racket frames

212
Q

What is the structure of metals? 3 points

A

Giant structure. Electrons in the outer shell of metal atoms are delocalised. There are strong forces of electrostatic attraction between positive metal ions and shared electrons which holds the atoms together in a regular structure known as metallic bonding (this is very strong)

213
Q

Identify 2 substances held together by metallic bonding

A

Alloys and metallic elements

214
Q

Why are most metals solid at room temperature?

A

Electrostatic forces between metal atoms and delocalised sea of electrons are very strong and need lots of energy to be broken so most compounds with metallic bonds have high melting and boiling points

215
Q

Why are metals good conductors?

A

Delocalised electrons carry current and heat energy through the whole structure

216
Q

Why are metals malleable?

A

Layers of atoms can slide over each other

217
Q

What does the state an element is at room temperature depend on? 4 things

A

How strong the attraction is between particles of the material which is dependant on: structure of the substance, type of bonds holding particles together, temperature, pressure

218
Q

PARTICLE THEORY:How do solids behave? 3 points

A

In solids there are strong forces of attraction between particles which holds them together in a fixed position to form a very regular fixed lattice arrangement. Particles don’t move from their positions so keep a definite shape and volume. Particles vibrate about their positions - the hotter the solid becomes the more they vibrate which causes the solid to expand slightly

219
Q

PARTICLE THEORY:How do liquids behave? 6 points

A

Weak forces of attraction between particles, randomly arranged and free to move past each other but tend to stick closely together, definite volume but don’t keep a shape, flow to fill the bottom of a container, constantly moving with random motion, the hotter they get the faster they move which means they expand slightly when heated

220
Q

PARTICLE THEORY:How do gases behave? 5 points

A

Forces of attraction between molecules are very weak so they are free to move far apart, particles travel in straight lines, don’t keep a definite shape or volume but always fill any container, move constantly with random motion, hotter the gas gets the faster the move so they either expand when heated or their pressure increases

221
Q

What are 2 negatives of particle theory?

A

Particles are not solid and inelastic and aren’t spheres, particle theory does not show forces between particles so there is no way of knowing how strong they are

222
Q

What happens when a solid is heated?

A

Particles gain more energy which makes them vibrate more which weakens the forces that hold the solid together. At melting point, particles have enough energy to break free from their positions (melting occurs)

223
Q

What happens when a liquid is heated?

A

Particles gain even more energy which makes them move faster which weakens and breaks bonds holding them together. At boiling point, articles have enough energy to break free from their positions (evaporation occurs)

224
Q

What happens as a gas cools?

A

Particles no longer have enough energy to overcome forces of attraction between them, bonds form between the particles. At boiling point many bonds have formed between the gas particles (condensation occurs)

225
Q

What happens when a liquid cools?

A

Particles have less energy so move around less, there isn’t enough energy to overcome attraction between particles so bonds form. At melting point so many bonds have formed that they are held in place (freezing occurs)

226
Q

What 2 things do physical changes in state change?

A

Not the particles but their arrangement or energy

227
Q

How do you work out percentage mass of an element in a compound?

A

(relative atomic mass x number of atoms of that element) divided by relative formula mass of the compound

228
Q

What is one mole of a substance?

A

The amount of that substance that contains an Avogadro number of particles (6.02 x 10^23)

229
Q

Why does the mole use such a long number?

A

The mass of that number of atoms or molecules of any substance is exactly the same number of grams as the relative atomic mass or relative formula mass of the element or compound

230
Q

How is mass conserved in a chemical reaction?

A

No atoms are destroyed, none are created so mass stays the same which can be shown adding up relative formula masses of substances on each side of a balanced symbol equation. Total Mr of reactants equals total Mr of products

231
Q

What is an explanation for an increase in mass during a chemical reaction?

A

One of the reactants is a gas that is found in air and all of the products are solid, liquid or aqueous. Before the reaction, the gas is floating in air, not contained in the reaction vessel so we cannot account for its mass. When the gas reacts to form part of the product it becomes contained inside the reaction vessel so total mass of the stuff inside the reaction vessel increases

232
Q

What is an explanation for an decrease in mass during a chemical reaction?

A

One or more of the products are gases but all the reactants are solids, liquids or aqueous. Before the reaction all reactants ate contained in the reaction vessel but if the vessel isn’t enclosed gases can escape when they form so their mass cannot be accounted for as they are no longer in the reaction vessel. The total mass of stuff inside the reaction vessel increases

233
Q

How can you use the masses of reactants and products of a reaction to work out the balanced symbol equation? 4 steps

A

Divide the mass of each substance by its relative formula mass to find number of moles, divide the number of moles in each substance by the smallest number of moles in the reaction, if any numbers aren’t whole multiply all the numbers by the same number to make them whole, write these numbers in front of chemical formulas in the reaction

234
Q

What is a limiting reactant?

A

A reactant which gets completely used up before the others, causing the reaction to stop therefore limiting the amount of product formed. Amount of limiting reactant is directly proportional to amount of product formed

235
Q

How do you make sure a reactant has been used up?

A

Add the other reactants in excess to see if the reaction has stopped

236
Q

How do you work out the mass of a product using the limiting reactant?

A

Write out balanced equation, work out relative formula masses of reactant and product you want, find how many moles there are of the substance you know the mass of, use balanced equation to work out how many moles there will be of the other substance (how many moles there will be made of this many moles of reactant), use number of moles to calculate mass

237
Q

What is the yield of a reaction?

A

Mass of a product

238
Q

Define concentration

A

Amount of a substance in a certain volume of a solution

239
Q

Equation for concentration

A

Mass divided by volume

240
Q

What is an indicator?

A

A dye that changes colour depending on whether it’s above or below a certain pH

241
Q

What is a wide range indicator?

A

An indicator containing a mixture of dyes that means they gradually change colour over a broad range of pH which means they are useful for estimating the pH of a solution

242
Q

How can you measure pH electronically?

A

Attach a pH probe to a pH meter and place the pH probe in the solution so the pH is given on digital display of the pH meter as a numerical value so this is more accurate than an indicator

243
Q

What is an acid?

A

Aqueous solution with a pH of less than 7 that forms H+ ions (PROTONS) in water

244
Q

What is a base?

A

Any substance that will react with an acid to form a salt

245
Q

What is an alkali?

A

A base that dissolves in water to form a solution with a pH greater than 7 and form OH- ions in water

246
Q

What is the word equation and the ionic equation for neutralisation?

A

acid + base -> salt + water. H+ + OH- -> H2O

247
Q

What is the difference between strong and weak acids?

A

Strong acids completely ionise in water (all acid particles dissociate to release H+ ions) whereas weak acids do not fully ionise (only a small proportion of acid particles dissociate). The ionisation of a weak acid is reversible which sets up an equilibrium between the undissociated and the dissociated acid (the equilibrium lies way to the left due to only a few of the particles releasing H+ ions)

248
Q

What is the pH of an acid a measure of?

A

The concentration of H+ ions in the solution. For every decrease of 1 on the pH scale the concentration of H+ ions increases by a factor of 10. Therefore, strong acids always have a lower pH than weak acids even If they have the same concentration

249
Q

Give 3 examples of strong acids

A

Hydrochloric, nitric, sulphuric

250
Q

Give 3 examples of weak acids

A

Ethanoic, citric, carbonic

251
Q

What is the difference between a concentrated and dilute acid?

A

Concentrated acids (labelled corrosive) have a higher total number of dissolved acid molecules in a given volume than dilute (labelled irritant). pH increases with concentration regardless of whether the acid is strong or weak

252
Q

What do all metal oxides and metal hydroxides react with acids to form?

A

A salt and water

253
Q

What do metal carbonates react with acids to form?

A

Salt + water + carbon dioxide

254
Q

Unit for concentration

A

g/dm^3

255
Q

When is a salt formed?

A

When the hydrogen in an acid is replaced by metal

256
Q

How do you form soluble salts from an insoluble base and an acid? 5 steps

A

React an acid and an insoluble carbonate or oxide to prepare an aqueous solution of a salt, heat up acid using Bunsen burner to speed up reaction then turn the Bunsen burner off, add carbonate/oxide until fizzing (which will occur) stops, filter the excess solid out of the solution, evaporate the filtrate using a water bath or electric heater to leave a concentrated solution of the salt which will crystallise after evaporating and cooling

257
Q

How do you form soluble salts from an acid and an alkali? 9 steps

A

Put the alkali into a conical flask using a pipette, put acid into burette, add indicator to alkali and place onto white tile to identify colour, place conical flask under burette, turn tap on burette to run acid into alkali, swirl it until you notice colour change, record how much acid you used, repeat the experiment without indicator, heat solution to evaporate

258
Q

Define neutralisation

A

When an acid and alkali act quantatively with each other, in a reaction in water neutralisation results in there being no excess of hydrogen or hydroxide ions in the solution

259
Q

What is a metal’s reactivity determined by?

A

How easily they lose electrons

260
Q

What is the reactivity series of metals?

A

Potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iodine, tin, lead, hydrogen, copper, silver, gold, platinum

261
Q

Why are carbon and hydrogen included in the reactivity series of metals? 2 points

A

This gives you information about how metals react with them: metals that are less reactive than carbon can be extracted from their ores by reduction with carbon, metals that are more reactive than hydrogen react with acids

262
Q

What do some metals react with acids to give off and how is the speed of this reaction calculated?

A

Salt and hydrogen gas. Rate at which bubbles of hydrogen are produced (the more reactive, the more bubbles)

263
Q

What do metals react with water to produce?

A

Metal hydroxide + hydrogen but less reactive metals like zinc, iron and copper do not react

264
Q

Why aren’t most metals found in their pure form on earth?

A

They tend to be fairly reactive so are found as compounds and have to be extracted before being used

265
Q

What is the formation of a metal ore an example of?

A

Oxidation (gain of oxygen)

266
Q

How can metals be extracted from their ores by reduction using carbon?

A

For metals which are less reactive than carbon, the oxygen is removed from their ore (it is reduced) and carbon gains oxygen so is oxidised. Carbon can only take oxygen away from metals which are less reactive than itself

267
Q

Give an example of a metal ore reduced using carbon

A

Iron oxide can be heated in a blast furnace to make iron

268
Q

How are metals which are more reactive than carbon extracted?

A

Electrolysis which is expensive because a lot of energy is required to melt the ore and produce the required current

269
Q

Define redox reaction

A

A reaction which involves both a reduction process and a complementary oxidation process. If electrons are transferred, it’s a redox reaction

270
Q

Give an example of a redox reaction when metals react with acids, give the ionic equation

A

Reaction of iron with sulphuric acid involces iron atoms losing electrons to become iron (II) ions (they are oxidised by hydrogen ions), hydrogen ions gain electrons to become hydrogen atoms (they are reduced by iron atoms). Fe + 2H+ -> Fe2+ + H2

271
Q

Give an example of a redox reaction in a halogen displacement, give the ionic equation

A

Chlorine can displace bromine from potassium bromide solution , chlorine atoms gain electrons to become chloride ions (they are reduced by bromide ions), bromide ions lose electrons to become atoms (they are oxidised by chlorine atoms). Cl2 + 2Br- -> 2Cl- + Br2

272
Q

What do ionic equations show?

A

The particles which are reacting and the products they form but not ions which are present that nothing happens to (spectator ions)

273
Q

Give an example of a redox reaction in a metal displacement

A

When you put iron into copper sulphate solution the iron displaces copper so you end up with iron sulphate solution (iron loses 2 electrons to become a 2+ ion so is oxidised) and copper metal (copper gains these 2 electrons to become a copper atom so is reduced)

274
Q

What does electrolysis involve? 6 points

A

An electric current is passed through an electrolyte (molten or dissolved ionic compound so ions are free to move), ions move towards electrodes where they react and the compound decomposes, positive ions move towards the cathode (negative electrode) to gain electrons and form atoms and negative ions move towards the anode (positive) to lose electrons and form atoms, this creates a flow of charge through the electrolyte as ions travel to electrodes. As ions gain or lose electrons they form the uncharged element and discharge from the electrolyte

275
Q

What should electrodes be made of and why?

A

An inert material so they don’t react with the electrolyte

276
Q

What is cryolite?

A

Aluminium based compound with a lower melting point than aluminium oxide (aluminium has a very high melting point which has to be reduced)

277
Q

How is aluminium extracted from the ore bauxite (containing aluminium oxide mixed with silicon dioxide)? 5 steps

A

Aluminium oxide mixed with cryolite to reduce melting point from 2000 to 900 degrees celsius, molten mixture contains free electrons so can conduct electricity, positive Al3+ ions attracted to negative electrode where they pick up three electrons each and turn into neutral aluminium atoms then sink to the bottom of the electrolysis tank, negative O2- ions attracted to positive electrode where each loses two electrons, neutral oxygen atoms combine to form O2 molecules

278
Q

In electrolysis of aqueous solutions, what ions are present in addition to the ions from the ionic compound?

A

H+ and OH- ions from the water

279
Q

What is the order of discharge from the anode?

A

If hydroxide and halide ions are present, halide ions discharge first and hydroxide is left in the container but if no halide ions hydroxide ions will be discharged and oxygen gas will be formed

280
Q

What is the order of discharge from the cathode?

A

If H+ ions and metal ions are present, hydrogen gas will be produced if the metals form an elemental compound which is more reactive than hydrogen because the less reactive thing discharges first. If the elemental compound is less reactive than hydrogen a solid layer of the pure metal will be formed which coats the cathode

281
Q

Positive test for oxygen

A

Relights a glowing splint

282
Q

Define electrolysis

A

Splitting up ionic substances using electricity

283
Q

How often does the graphite anode need to be replaced?

A

Every 28 days

284
Q

Why does the graphite anode get smaller in electrolysis?

A

Oxygen reacts with graphite which burns away to form carbon dioxide

285
Q

What happens to the more reactive elements in electrolysis?

A

They are left in the container to form a compound

286
Q

Why is electrolysis of aqueous solutions complex?

A

Due to the presence of ions formed when water ionises

287
Q

Ionic equation for electrolysis

A

H2O > H+ + OH- (reverse of neutralisation)

288
Q

How is energy moved around in reaction (but still conserved)? 2 ways

A

If products of a reaction store more energy than original reactants they must have taken in the difference in energy between the products and reactants, if they store less then the excess energy was transferred to the surroundings during the reaction

289
Q

What are 3 examples of an exothermic reaction?

A

Combustion, neutralisation, oxidation

290
Q

Give 2 uses of exothermic reactions

A

Hand warmers can use exothermic oxidation of iron in air with a salt solution catalyst to release energy, self heating cans of hot chocolate and coffee rely on exothermic reactions between chemicals in their bases

291
Q

Identify two examples of endothermic reactions

A

Much less common. Reaction between citric acid and sodium hydrogen carbonate, thermal decomposition

292
Q

Identify a use of endothermic reactions

A

Chemical reactions in sports packs allow them to become instantly cooler without having to put them in the freezer

293
Q

How can you investigate energy transfer? 3 steps

A

Measure amount of energy released by a chemical reaction in solution by making sure the temperature of the reagents is the same, mixing them in a polystyrene cup, measuring temperature of solution at the end of reaction

294
Q

What is the problem with energy measurements and how can it be reduced?

A

Energy lost to surroundings. Put the polystyrene cup into a beaker of cotton wool to give more insulation and putting a lid on the cup to reduce energy lost by evaporation

295
Q

How can you test the effect of acid concentration on the energy released in a neutralisation reaction between hydrochloride acid and sodium hydroxide? 6 steps

A

Put 25cm^3 of 0.25mol/dm^3 of hydrochloric acid and sodium hydroxide in separate beakers, place beakers in water bath at 25 degrees Celsius until they are both 25 degrees Celsius, add HCl followed by NaOH to a polystyrene cup with a lid, take temperature of mixture every 30 seconds, record the highest temperature, repeat steps using 0.5mol/dm^3 then 1mol/dm^3

296
Q

What happens in a chemical reaction? 4 things

A

Old bonds broken, new bonds made, energy must be supplied to break existing bonds (endothermic), energy is released when new bonds are formed (endothermic)

297
Q

What is activation energy?

A

The minimum amount of energy needed by reactants for them to collide and react. The greater the activation energy, the more energy needed to start the reaction -this has to be supplied for example by heating the mixture

la química (2 decks)

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