Giant Chemistry flashcard set
(178 cards)
1
Q
Who made the nuclear model?
A
Rutherford
2
Q
What is the difference between the plum pudding model and the nuclear model?
A
-the plum pudding suggests that there’s no empty space inside the atom whereas the nuclear model suggests it is mostly empty space
-mass in the plum pudding model is distributed equally whereas mass is concentrated in the nucleus in the nuclear model
-in the plum pudding model there are negative electrons embedded in a sea of positive charge whereas in the nuclear model, the positive charge is concentrated at the centre
3
Q
what is the charge of an atom?
A
neutral- the number of protons is equal to the number of electrons
4
Q
what is the radius of an atom
A
0.1nm
5
Q
what is the radius of a nucleus in comparison to the atom?
A
it is less than 1/ 10,000 of the atom
6
Q
What is the relative atomic mass of an atom?
A
an average value that takes account of the abundance of the isotopes of the element
7
Q
What are the advantages of dot and cross diagrams?
A
show movement of electrons and where they came from
8
Q
what are the disadvantages of dot and cross diagrams
A
-don’t show relative size
-not 3D
9
Q
What are the advantages of the ball and stick model?
A
-does show 3D arrangement
-shows bonding between atoms
10
Q
what are the limitations of the ball and stick model?
A
-fails to show electrons
-distance between atoms is inaccurate
11
Q
what are the advantages of 2D representations- displayed formula?
A
show arrangements of atoms in a molecule and bonding
12
Q
What are the limitations?
A
-doesn’t show relative size
-isn’t 3D- not an accurate representation
13
Q
How was the periodic table developed before the discovery of sub-atomic particles?
A
scientists attempted to classify the elements by arranging them in order of their atomic weight
14
Q
What was the issue with this?
A
table was incomplete and elements were placed in inappropriate groups if atomic weight rule was strictly followed
15
Q
How did Mendeleev overcome these problems?
A
left gaps for elements that hadn’t yet been discovered
organised elements by increasing atomic mass
grouped those with similar chemical properties
16
Q
What are the differences between metals and non-metals
A
-metals are good conductors- they have a sea delocalised electrons whereas non-metals are poor conductors
-metals have a higher melting point due to strong metallic bonds
-metals are malleable due to weak intermolecular bonds between layers which can slide over eachother without breaking the overall structure whereas non-metals are brittle
17
Q
why do boiling points increase going down group 0?
A
-increasing atomic mass
-intermolecular forces become stronger
-more energy required to break these forces
18
Q
How do alkali metals react with oxygen?
A
-produce metal oxides
-reaction becomes more vigorous going down the group
19
Q
How do alkali metals react with water?
A
-react vigorously
-metal hydroxide and hydrogen gas
-releases heat
20
Q
how do alkali metals react with chlorine?
A
-react vigorously
-produce chlorides: white solids at room temperature which dissolve in water to make a neutral solution
21
Q
What happens when chlorine, bromine and iodine react with metals?
A
they form ionic compounds called metal halides
22
Q
What happens where chlorine, bromine and iodine react with non-metals?
A
-they form covalent compounds with simple molecular structures
23
Q
Can you describe the trends of the halogens as you go down the group?
A
In Group 7, the further down the group an element is the higher its
relative molecular mass, melting point and boiling point
24
Q
What happens to reactivity as you go down group 7?
A
it decreases
25
What happens in a displacement reaction?
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
26
What are the property differences between transition metals and group 1?
-transition metals have a higher melting and boiling point to group 1 metals
-they have a greater density
-group 1 metals react vigorously with the air whereas transition metals react more slowly with oxygen and may require heating
-Group 1 metals react vigorously with water whereas transition metals react more slowly or not at all
-alkali metals are softer but transition metals are stronger
27
what are the properties of transition metals?
-they have multiple oxidation states (form ions with different charges)
-form coloured compounds
-can be used as catalysts
28
what happens during ionic bonding?
-the particles are oppositely charged ions
-metals and non-metals
-form strong electrostatic bonds
-involves the transfer of electrons
29
what happens during covalent bonding?
-two non-metals
-atoms which share electrons
30
what happens during metallic bonding?
-atoms which share delocalised electrons
-occurs in metallic elements and alloys
31
can you describe an ionic compound?
-giant lattice structure
-ionic compounds are held together by strong electrostatic forces of attraction
-forces act in all directions
32
Can you describe the structures that covalent bonds form
-small molecules.
-large molecules, such as polymers
- giant covalent structures,
such as diamond and silicon dioxide.
33
Can you describe the structures that metallic bonding describes?
-regular pattern
-layers can easily slide over eachother
-electrons in outer shell of metal atoms are delocalised (free to move throughout structure)
-sharing of these delocalised electrons creates strong metallic bonds
34
What does the amount of energy to change state depend on?
the strength of the particles of the substance
35
What are the limitations of the particle model?
-no forces
-all particles are represented as spheres
-all spheres are solid
36
What are the properties of ionic compounds?
-strong electrostatic charges in all directions
-regular structures (giant ionic lattices)
-high melting and boiling points
-when molten or dissolved in water, they conduct electricity because ions are free to move so charge can flow
37
what are the properties of small covalent molecules?
-strong covalent bonds
-weak intermolecular forces (overcome when substance melts or boils not covalent bonds)
-intermolecular forces increase with molecular size, larger molecules have higher melting/boiling points
-don't conduct- molecules don't have an overall charge
38
What are the properties of polymers?
-large molecules
-strong covalent bonds between atoms
-intermolecular forces between molecules are relatively strong
-solids at room temp
39
what are the properties of giant covalent structures?
-solids
-very high melting points
-strong covalent bonds
-diamond and graphite (carbon allotropes ) and silicon dioxide are examples
40
what are the properties of metals and alloys?
-giant structures of atoms
-strong metallic bonding
-arranged in layers (malleable)
-mixed with other metals which disrupt regular structure due to different size of atoms to make alloys which are harder
41
What is the structure of diamond?
-each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure
-diamond is very hard, has a high melting point and doesn't conduct electricity (no delocalised electrons)
42
What is the structure of graphite?
-each carbon atom forms 3 covalent bonds forming layers of hexagonal rings with no covalent bonds between the layers
-in graphite one electron from each carbon atom is delocalised (only forms 3 covalent bonds)
-conducts electricity
43
what is graphene?
a single layer of graphite
44
What are the properties of graphene?
strong covalent bonds between the carbon atoms mean that graphene has:
-a high melting point
-is very strong
45
what are fullerenes?
-molecules of carbon atoms with hollow shapes
-based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms
46
What was the first fullerene to be discovered?
Buckminsterfullerene
47
What are the properties of Buckminsterfullerene?
-spherical molecules are made up of 60 carbon atoms joined together by strong covalent bonds
-weak intermolecular forces between molecules
-slippery and has a low melting point due to weak intermolecular forces
48
What are nanotubes and what are their properties?
Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios
-high tensile strength-resist being stretched
-conduct electricity
49
What are the uses of fullerenes?
-they can form spheres around other molecules acting like a cage: can be used to transport drugs in the body
-large SA:V ratio- can be used to make industrial catalysts
-nanotubes are used to strengthen materials e.g in tennis rackets: high length: diameter ratio allows them to add strength without much weight
50
what is the diameter of a nanoparticle?
1nm-100nm
51
What are the uses of nanoparticles
-large SA:V ratio
-used as catalysts: exposed surface area is more important than their volume- we need much less of a material made of nanoparticles
-size of fullerenes means they can easily access our cells to deliver drugs
-some nanoparticles conduct electricity- used to make tiny computer chips
-silver nanoparticles have antibacterial properties: can be infused into surgical masks and wound dressings to kill bacteria
52
What risks are associated with nanotechnology?
-relatively new: effects on bodies aren't known e.g in suncream: whilst nanoparticles provide better skin coverage we don't know whether they are able to get into our bodies and the effect that may have
53
What is the relative formula mass (Mr) of a compound?
the sum of the relative atomic masses of the atoms in the numbers shown in the formula.
54
How do you how do you calculate the percentage by mass in a compound?
% mass = (Total Ar of the element ÷ Mr of the compound) × 100
e.g The percentage of calcium in CaCO3 = (40 ÷ 100) × 100 = 40%
55
How does the Law of the Conservation of Mass link to the formula mass of the products and reactants in a chemical reaction?
in a balanced chemical equation, the total formula mass of the reactants should be equal to the total formula mass of the products, based on the law of conservation of mass.
56
What does one mole of a one substance contain compared to one mole of another?
One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance.
57
What does the Avogadro constant refer to?
The number of atoms, molecules or ions in a mole of a given substance
58
What is the value of the Avogadro constant?
6.02 x 10^23 per mole
59
What is the equation to find moles?
moles= mass/Mr
60
How do you use moles to balance equations?
use the mass and relative formula mass of each substance in an equation to find the number of moles- this number is the coefficient
61
What does 'moles' refer to in chemistry?
the amount of a substance
62
What do the coefficients (numbers in front of the formulae) represent in chemical equations?
the number of moles of each substance
63
What does the limiting reactant refer to?
the reactant that is completely used up- in chemical reactions, it is common to use an excess of one of the reactants to ensure the other is completely used up
64
How do you calculate the mass of the product using the idea of the limiting reactant?
the product will have the same amount of moles as the limiting reactant (the excess reactant will not have reacted to form a product) so you can determine the number of moles of product and multiply it by its relative formula mass (Mr)
65
what is the percentage yield?
The percentage yield shows how much product is obtained compared to the maximum possible mass
66
Why might the percentage yield of a product be less than 100%?
loss when filtering
loss when
evaporating
loss when transferring liquids
not all reactants reacting to make product
67
How do you calculate the percentage yield of a product?
percentage yield= mass obtained/ expected mass x 100
68
What is the definition of atom economy?
it's a measure of the amount of starting materials that end up as useful products
69
Why is this important?
by minimising the production of unwanted products, we save money and increase sustainability
70
How do we calculate atom economy?
atom economy= relative formula mass of desired products from equation / relative formula masses of all reactants from equation
71
What is the concentration of a solution measured in?
mol/ dm^3
72
How do you calculate moles using concentration and volume?
moles = concentration x volume
73
How do you calculate concentration using mass and volume
concentration= mass/ volume
74
What is concentration measured in?
g/dm^3
75
Equal amounts in moles of gases occupy...
the same volume under the same conditions of temperature and pressure.
76
What is the volume of one mole of any gas at room temp and pressure (20 degrees and 1 atmosphere pressure)?
24 dm^3
77
How do you calculate the volume of a gas?
volume = number of moles x 24
78
What is the reactivity of a metal related to?
its tendency to form positive ions
79
What two non-metals do they use in the reactivity series?
carbon and hydrogen
80
What is the structure of the reactivity series?
Please- Potassium
Stop- Sodium
Calling- Calcium
Me- Magnesium
A - Aluminium
Careless- Carbon
Zebra- Zinc
Instead- Iron
Try - Tin
Learning- Lead
How- Hydrogen
Copper - Copper
Saves - Silver
Gold- Gold
81
Why do some metals need to be extracted from a compound when some do not?
Some metals, such as gold, are so unreactive that they can be found in the earth as the metal itself whereas others react with the air to form compounds
e.g copper oxide
82
How does the displacement of metals link to extraction?
You can extract a metal compound by reacting it with a more reactive metal to displace it from its compound
83
How do you displace metals from their oxides using carbon?
Metals less reactive than carbon can be extracted from their oxides by reduction with carbon
84
What element do all acids contain?
Hydrogen
85
What two products are made when acids react with metals?
Salt+ Hydrogen
86
What is a salt?
a substance produced when the hydrogen in an acid is replaced by a metal
87
Why does Magnesium react vigorously with acids?
Magnesium can easily displace Hydrogen from acids- it is higher in reactivity series
88
What do all acids release in aqueous solutions?
Hydrogen
89
How do you write ionic equations?
1) write the ions for the aqueous substances- solids, liquids and gases stay the same
2)cross out the spectator ions- the ones that don't change
3) rewrite equation without spectator ions
90
What is a neutralisation reaction?
a reaction between an acid and a base
91
92
What is the difference between alkalis and bases?
A base is a something that reacts with an acid to form water and a salt. An alkali is any base that is soluble in water.
93
What are the different types of reactions with acids?
metal oxide+ acid----> salt+ hydrogen
metal hydroxide + acid---> salt+ hydrogen
metal carbonate + acid ---> salt + hydrogen + carbon dioxide
94
What salt does hydrochloric acid produce?
Chlorides
95
What salt does sulfuric acid produce?
Sulfates
96
What salt does nitric acid produce?
Nitrates
97
How can soluble salts be made?
from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates.
98
What two ways can be used to measure pH?
universal indicator
pH probe
99
What happens in neutralisation reactions between an acid and alkali?
In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water.
100
What do alkalis and acids produce in aqueous solutions?
acids produce hydrogen (H+) ions
alkalis produce hydroxide (OH-) ions
101
What defines a strong acid?
A strong acid is completely ionised in aqueous solution.
102
What defines a weak acid?
A weak acid is only partially ionised in aqueous solution.
103
What happens as the pH decreases by one unit?
the hydrogen ion concentration of the solution increases by a factor of 10
104
What is the difference between a dilute and a concentrated acid?
a dilute solution contains a relatively small amount of dissolved solute
a concentrated solution contains a relatively large amount of dissolved solute
105
What is an electrolyte?
an ionic compound that conducts electricity as it is molten or dissolved in water
106
What causes ions to move towards the electrodes?
passing an electric current through the electrolyte as this causes one electrode to be positively charged and the other to be negatively charged
107
What is the negatively charged electrode called in electrolysis?
the cathode
108
what is the positively charged electrode called?
the anode
109
What happens to the ions at the electrodes?
they are discharged and become neutral atoms through oxidation/ reduction
110
When is electrolysis used to extract metals?
Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon
111
What is Aluminium ore called?
Bauxite
112
How does it reach a state where it can be reduced and Aluminium can be extracted?
The bauxite is purified to yield a white powder – aluminium oxide (also known as alumina) – from which aluminium can be extracted
113
Why is a mixture of cryolite and Aluminium oxide used as the electrolyte?
cryolite reduces the overall melting point of the mixture which reduces the energy required for the electrolysis process- more cost effective
114
Why does the positive anode (made of carbon) need to be replaced in the electrolysis of aluminium oxide?
oxygen is displaced at the anode
it will react with the carbon
the electrode will gradually burn away
115
In the electrolysis of aqueous solutions, the ionic compound is dissolved in water, what ions does H2O separate into?
H+
OH-
116
What are the formula of these ionic compounds:
?
117
In the electrolysis of the ionic compound-
CuSO4 dissolved in water- what ions will be attracted to the cathode?
Cu^2+
H+
118
Which of the two ions will be reduced at the cathode?
Hydrogen will be discharged at the cathode if the metal is more reactive than hydrogen- in this case, copper will be discharged because it is less reactive
119
In the electrolysis of the ionic compound-
CuSO4 dissolved in water- what ions will be attracted to the anode?
SO4^2-
OH-
120
Which ion will be discharged?
At the positive electrode (anode), oxygen is produced unless the solution contains halide ions when the halogen is produced
In this case, the hydroxide ion will be discharged
121
What happens at the cathode?
During electrolysis, at the cathode (negative electrode), positively charged ions gain electrons and so the reactions are reductions
122
What happens at the anode?
At the anode (positive electrode), negatively charged ions lose electrons and so the reactions are oxidations
123
What kind of electrodes do scientists use to prevent reactions occuring?
inert electrodes (e.g made of Platinum due to unreactive nature)
124
What will the half equation be for the reduction reaction?
2H+ + 2e- → H2
125
What will be the half equation for the oxidation reaction?
4OH- → O2 + 2H2 O + 4e-
(Hydroxide becomes water and oxygen)
126
Do endothermic reactions transfer energy to or from the surroundings?
from
127
What does this mean for the temperature of the surroundings?
it decreases
128
What are some applications of endothermic reactions?
sports injury packs
129
What are some examples?
thermal decompositions
130
Do exothermic reactions transfer energy to or from the surroundings?
to
131
What does this mean for the temperature of the surroundings
it increases
132
What are some applications of exothermic reactions
self-heating cans
hand warmers
133
What are some examples?
combustion
oxidation reactions
neutralisation reactions
134
What is the minimum amount of energy required to start a chemical reaction?
activation energy
135
On a reaction profile, what shows the activation energy?
the difference in energy between the reactants and the peak of the 'hump'
136
On a reaction profile, what shows the overall energy change?
the difference in energy between the products and the reactants
137
Is the product line higher or lower than the reactant line in an endothermic reaction profile?
it is higher
138
Is the product line higher or lower than the reactant line in an exothermic reaction profile?
it is lower
139
During a chemical reaction, does it require or release energy when bonds are broken?
it requires energy
140
During a chemical reaction, does it require or release energy when new bonds are formed?
it releases energy
141
What describes the overall energy change of a reaction?
The difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed
142
What are bond energies?
the energy required to break one mole of a particular bond
143
How can you use this information to work out the energy change of the reaction?
energy change= energy taken in to break bonds of the reactants- energy released when the bonds of the products form
144
What is energy change measured in?
kJ/mol
145
Why is the energy change negative for exothermic reactions?
The energy change is negative, due to the fact that the energy released by the bonds formed is greater than the energy absorbed by the bonds broken.
146
How can a simple cell be made
A simple cell can be made by connecting two different metals in contact with an electrolyte.
147
What do batteries consist of?
Batteries consist of two or more cells connected together in series to provide a greater voltage.
148
In non-rechargeable cells and batteries, when do the chemical reactions stop?
the chemical reactions stop when one of the reactants has been used up.
149
How do you increase the voltage of the cells?
If the electrodes have a large difference in reactivity between them, then the potential difference of the cell will be bigger.
150
Can you name an example of a non-rechargeable battery?
alkaline batteries
151
How can cells and batteries be recharged?
Rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied.
152
How do cells generate electricity?
they convert chemical energy into electrical energy through chemical reactions
153
What are the two main supplies of fuel cells?
In order to make electricity, fuel cells will use an external source of fuel and oxygen. The source of fuel could be an element such as hydrogen.
154
How does a fuel cell generate electricity?
Fuel is electrochemically oxidised. When fuel enters the cell, it reacts with oxygen. This occurs through an oxidation reaction, resulting in the creation of a potential difference inside the cell
155
What does the reaction of a hydrogen fuel cell involve?
The overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce water
156
What is the half equation for the oxidation reaction taking place at the cathode (the positive electrode, opposite of electrolysis) ?
Hydrogen loses electrons at the cathode:
H2 → 2H+ + 2e–
157
What is the half equation for the reduction reaction taking place at the anode (the negative electrode)?
Oxygen gains electrons at the anode:
O2 + 4e– → 2O2–
158
What are the advantages of hydrogen fuel cells?
Hydrogen can be produced from water so the process is renewable
They do not produce any pollution: the only product is water whereas petrol engines produce carbon dioxide, and oxides of nitrogen
They release more energy per kilogram than either petrol or diesel
No power is lost in transmission as there are no moving parts, unlike an internal combustion engine
Quieter so less noise pollution compared to a petrol engine
159
What are the disadvantages of hydrogen fuel cells?
Hydrogen obtained by methods that involve:
-The combustion of fossil fuels releases carbon dioxide and other pollutants into the atmosphere
-The electrolysis of water requires large amounts of electricity to produce
Materials used in producing fuel cells are expensive
Hydrogen is more difficult and expensive to store compared to petrol as it is very flammable and easily explodes when under pressure
Fuel cells are affected by low temperatures, becoming less efficient
There are only a small number of hydrogen filling stations across the country
160
What is one way to measure rate of reaction?
mean rate of reaction= quantity of reactant used/ time taken
161
Describe another way in which one can measure rate of reaction?
mean rate of reaction= quantity of product formed/ time taken
162
What is the quantity of reactant or product measured in?
by mass: g
by volume: cm^3
163
What may the units of rate of reaction be given as?
g/s
cm^3 / s
164
What factors affect the rate of a chemical reaction?
the concentrations of reactants in solution
the pressure of reacting gases
the surface area of solid reactants
the temperature
the presence of catalysts
165
How does increasing pressure affect the rate of reaction?
If the pressure of gaseous reactants is increased, there are more reactant particles for a given volume. There will be more collisions and so the reaction rate is increased. The higher the pressure of reactants, the faster the rate of a reaction will be.
166
How does increasing concentration impact the rate of reaction?
increases number of successful collisions increases the rate of reaction
more reactant particles moving in a given space
167
How does increasing temperature affect the rate of reaction?
speeds up reaction
higher temps= particles have greater kinetic energy
collide more frequently and with greater energy= increases number of successful collisions
168
How does increasing the surface area impact the rate of reaction?
larger surface area means that more particles are exposed
more frequent collisions
greater chance of successful collisions
increases rate of reaction
169
How does the presence of a catalyst impact the rate of reaction?
A catalyst increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. This means that more particles have the necessary energy to react, leading to more successful collisions and a faster reaction rate
170
What does collision theory suggest?
chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.
171
What is a pure substance?
a pure substance is a single element or compound, not mixed with any other substance
172
What is a key thing to consider about pure substances and their melting and boiling points?
Pure elements and compounds melt and boil at specific temperatures
173
What is a formulation?
A formulation is a mixture that has been designed as a useful product.
174
How are they made?
Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
175
What are some examples of formulations?
Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
176
What is the test for hydrogen?
The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound
177
What is the test for oxygen?
The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.
178
What is the test for carbon dioxide?
The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy).
