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iGCSE Chemistry > Principles of Chemistry > Flashcards

Principles of Chemistry Flashcards

1
Q

Name the processes responsible for the following phase change: solid→gas

A

Sublimation (s to g)
Deposition (g to s)

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2
Q

Define diffusion

A

Overall movement of particles from an area of high concentration to an area of low concentration

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3
Q

What is a solubility curve?

A

It is a curve that shows how the solubility of a substance (in grams 100g of water), changes with temperature.

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4
Q

Outline the main assumptions of the kinetic theory of matter

A

1) Matter is made up of ions, molecules and atoms of different sizes
2)At the same temp, small particles move faster than larger particles
3)As temp rises, the particles have more kinetic energy and move faster
4)Solids are made up of ordered arrangement of closely packed particles
5)Liquids do not have particles arranges regularity. Particles move around
6)In gases, the particles are far apart. They move fast. This motion is random.

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5
Q

Explain what is meant by centrifuging

A

Method for separating out particles of different densities in a substance.
It can be used to separate suspended solids (very small particles of solid), from the liquid they are suspended in.

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6
Q

Define Compounds

A

Elements combine through chemical reactions to form new products.

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7
Q

Define element

A

An element is a substance made up of only one atom

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8
Q

Define mixture

A

Two or more elements or compounds not chemically combined together

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9
Q

What are the 5 methods through which mixtures can be separated?

A

-Filtration
-Evaporation/Crystallisation
-Simple distillation
-Fractional distillation
-Chromatography

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10
Q

Describe and explain simple distillation

A

Simple distillation is used to separate liquid from a solution. The liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid.

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11
Q

Describe and explain evaporation/crystallisation

A

Evaporation is a technique for separation of a solid dissolved in a solvent. The solution is heated until all the solvent evaporates; the solids stays in the vessel.

Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution. Then, we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration

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12
Q

Describe and explain fractional distillation

A

Technique for seperation of a mixture of liquids. Only works when the liquids have different boiling points. Apparatus similar to the one of simple distillation, with an additional fractionating column placed on top of the heated flask. The fractionating column contains glass beads. It helps to separate the compounds. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the column.

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13
Q

Describe and explain filtration

A

Filtration is used to separate an insoluble solid suspended in a liquid. The insoluble solid gets caughts caught in the filter paper. The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel.

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14
Q

Describe and explain chromatography

A

Chromatography is used to separate a mixture of substances dissolved in a solvent.

Place a piece of paper with a spot containing a mixture in a beaker with some solvent. The solvent level will rise, thus separating the spot into few spots (components).

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15
Q

Describe the paper chromatography experiment.

A

1.Start line drawn at the bottom of paper. Mixture spotted on the line.
2.Beaker is filled with a small amount the solvent
3.Paper is hung
4.Solvent travels up the paper
5.Before the solvent level reaches the end, the paper is taken out and the finish line is marked. Paper is dried.

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16
Q

Formula for Rf

A

Distance moved by solute (the spot)/distance moved by solvent

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17
Q

Explain why atoms are electrically neutral

A

They have the same number of electrons and protons.

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18
Q

Define Atomic number

A

The number of protons in the nucleus

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19
Q

Atoms of the same element have the same number of which particle in the nucleus?

A

Protons

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20
Q

What is the mass number?

A

The total number of protons and neutrons in the nucleus.

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21
Q

How does one calculate the number of neutrons using mass number and atomic number?

A

Subtract the atomic number from the mass number.

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22
Q

Define isotope.

A

Atoms of the same element, that have a different number of neutrons.

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23
Q

What is the relative atomic mass?

A

The average mass value of one atom (taking into account the abundance of isotopes), compared to 1/12 of one carbon 12-atom

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24
Q

Describe the properties of noble gases

A

-Non-metals
-Colourless gases at room temp
-Low boiling points
-Unreactive
-Boiling point increases down the group

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25
Q

Which are the elements that react to form positive ions?

A

Metals

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26
Q

Explain the following: solute, solvent, solution, miscible, immiscible, soluble, insoluble.

A

A solute is a substance that is dissolved in a solvent. Together, they form a solution

Miscible refers to the substances (particularly liquids), that mix together in all proportions. Water and oil are immiscible.

Soluble refers to the substance that can be dissolved in a solvent. An insoluble substance wont dissolve in a particular solvent.

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27
Q

What are the rows of a periodic table called?
What are the columns of a periodic table called?

A

-Period
-Group

28
Q

Elements in Group 1 are known as…?

A

Alkali Metals

29
Q

Elements in Group 7 are known as…?

A

Halogens

30
Q

Define ionic bonding.

A

Ionic bonding is the transfer of electrons from a metal atom to a non-metal to form positive and negative ions. There is a relatively strong electrostatic attraction between the positive and negative ions which is called an ionic bond.

31
Q

How are ionic compounds held together?

A

Electrostatic attraction.

32
Q

Properties of ionic substances.

A

-High melting and boiling point (because of the strong electrostatic forces between oppositely charged ions).
-Do not conduct electricity when solid.
-Conduct when molten or dissolved in water (ions are free to move).

33
Q

5 examples of both positive and negative ions

A

+= Ag+, H+, NH4+, Pb (2+), Cu(2+), Zn(2+), Fe(2+) Fe(3+)
-=OH-, CO3(2-), NO3-, SO4(2-)

34
Q

How are ionic compounds formed? Explain in terms of MgO case

A

-Reaction of a metal and a non metal
-Electron transfer occurs-metal gives away its outer shell electrons to nonmetal
Mg is in Group II, so has 2 outer shell electrons
O is in group VI, so can accept 2 electrons to get a full outer shell configuration
Mg becomes Mg2+ and O becomes O2-

35
Q

Define Covalent bond

A

Shared pair of electrons between two atoms.

36
Q

How do intermolecular forces change as the mass/size of the molecule increases?

A

They increase. That causes melting/boiling points to increase as well (more energy needed to overcome these forces).

37
Q

Properties of covalent bonds

A

-Do not conduct electricity
-Small molecules
-Weak intermolecular forces
-Low melting and boiling points

38
Q

What are giant covalent substances (with examples)?

A

Atoms covalently bonded together in a giant lattice.
-High melting and boiling points
-Mostly don’t conduct electricity
Diamond, graphite, silicon dioxide, fullerene

39
Q

Properties of metals

A

-High melting and boiling points
-High density
-Good conductors of heat and electricity
-Malleable, soft

40
Q

Allotropes definition

A

different forms of the same element in the same physical state; the atoms are bonded differently.

41
Q

Describe and explain the properties of allotropes of carbon

A

Diamond
-4 strong covalent bonds for each carbon atom
-Very hard strong bonds
-Very high melting point
-Does not conduct electricity
Graphite:
-Three covalent bonds for each carbon atom
-Layers of hexagonal rings
-High melting point
-Layers free to slide as weak intermolecular forces
Fullerenes:
-Hollow shaped molecules
-Based on hexagonal rings but may have 5/7-carbon rings
-C60 has a spherical shape, simple molecular structure (Buckminsterfullerene)
Nanotubes:
-Cylindrical fullerene with high length to diameter ratio
-High tensile strength
-Conductivity
Graphene-a single layer of graphite

42
Q

What is metallic bonding

A

Forces of attraction between delocalised electrons and nuclei of metal ions.

43
Q

Define alloys

A

Mixtures of metals with other elements harder than metals because the different sizes of atoms distorts the layers, so they can’t slide over each other, therefore alloys are harder than pure metals.

44
Q

What are the limitations of the simple model?

A

There are no forces between spheres and atoms, molecules and ions are solid spheres-this is not true

45
Q

What does the amount of energy needed to change state from solid to liquid or liquid to gas depend on?

A

The strength of the forces between the particles of the substance. It depends on the bonding and if the forces are stronger the higher melting and boiling point.

46
Q

A pure substance will melt or boil at…?

A

A fixed temperature. A mixture will melt over a range of temperatures.

47
Q

What is the law of conservation of mass?

A

It states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.

48
Q

What’s Avogrado’s constant?

A

6.02x10²³

49
Q

Formula linking mass, moles, and mr

A

mass/molesxmr

50
Q

Formulas (2) linking concentration, mass and volume.

A

Conc. (g/dm³)=mass/vol
Con. (mol/dm³)=nr of moles/vol

51
Q

Percentage yield formula

A

actual/max. theoretical x100

52
Q

Define relative atomic mass and relative formula mass

A

RAM-Average mass of an atom is an element taking into account the masses and abundance of its isotopes, relative to the 1/12 of the mass of one 12C atom
RFM-SUM of RAMs of all atoms in the formula

53
Q

State what we mean by a limiting reactant in a chemical reaction

A

In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactants is used. The reactant that is completely used up is called the limiting reactant because it limits the amount of products formed

54
Q

Write down the formula that links concentration, mole/mass and volume together

A

moles/ conc. (mol/dm³) x Volume (dm³)

55
Q
A
56
Q

What is the molar volume of a gas at room temperature

A

1 mole of gas at room temp occupies 24 dm³

57
Q

What is titration

A

A technique for finding the concentration of a solution by reacting a know volume of this solution with a solution of known concentration

58
Q

Why is it not always possible to obtain the theoretical amount of product in a chemical reaction

A

-The reaction may not go to completion because it is reversible
-Some of the product may be lost when it is separated from the reaction mixture
-Some of the reactants may react in ways to different to the expected reaction

59
Q

What is atom economy

A

A measure of the amount of starting materials that end up as useful products.
It is a ratio of the relative formula mass of desired products to the sum of relative formula masses of all reactants.

60
Q

What is electrolysis

A

The passing of an electric current through ionic substances that are molten or in solution to break them down into elements; ions are discharged (the lose/gain electrons) at electrons to produce these.

61
Q

What is an electrolyte

A

The liquid/solution which conducts electricity

62
Q

What is a cathode or anode

A

Cathode is the negative electrode, anode is the positive electrode.

63
Q

What occurs at the cathode and what occurs at the anode during electrolysis?

A

Reduction and oxidation, respectively

64
Q

How is aluminium manufactured?

A

Electrolysis of aluminium oxide and cryolite-large amounts of energy needed to produce a current

65
Q

Why is cryolite used in the manufacturing of aluminium?

A

It lowers the melting point of aluminium oxide, reducing energy costs.

66
Q

When do you have to use electrolysis to extract metals?

A

Metals that are more reactive than carbon

iGCSE Chemistry (5 decks)

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