C2 Flashcards
1
Q
What is a compound?
A
When two or more elements are chemically bonded combined together. This makes it very hard to separate out again.
2
Q
What is a mixture?
A
When two or more substances are mixed together and can be easily separated.
3
Q
What are isotopes?
A
Different atomic forms of the same element, which have the same number of protons but a different number of neutrons. (they have the same atomic number but different mass numbers).
4
Q
How can the element Carbon-14 be used?
A
C-14 is unstable. When things die, the C-14 is trapped inside the dead material and gradually decays into nitrogen. By measuring the proportion of C-14 in some old wood you can calculate how long ago it was alive.
5
Q
What is ionic bonding?
A
When atoms lose or gain electrons to form charged particles, called ions, which are strongly attracted to each other (because of the attraction of opposite charges).
6
Q
What happens when an atom loses electrons?
A
The atom becomes positively charged.
7
Q
How does an atom lose an electron?
A
- Atoms on the left hand side of the periodic table have only one or two electrons in their outer shells.
- Therefore, it is easier for them to lose an electron and give it to another atom.
8
Q
What happens when an atom gains electrons?
A
The atom becomes negatively charged.
9
Q
How does an atom gain electrons?
A
- The elements in Group 6 and 7 have nearly full outer shells.
- Therefore, it is easier for them to take an electron from another element.
10
Q
What structure does an ionic bond produce and why?
A
They form giant ionic structures because of the strong electrostatic forces of attraction between the oppositely charged ions.
11
Q
What are the properties of an ionic compound?
A
- They all have high melting points.
- They all have a high boiling points
- They all dissolve easily in water
12
Q
Why do ionic compounds have high boiling and melting points?
A
Because of the strong forces of attraction between the ions.
13
Q
What happens when an ionic bond does melt?
A
The ions become free to move and they will be able to carry an electrical current.
14
Q
What happens when an ionic bond dissolves in water?
A
The ions separate and are free to move in the solution. They will be able to carry an electrical current as well.
15
Q
What are the properties of an ion?
A
- They have the electronic structure of a noble gas
- The charge of the positive ions are the same as the group number they are in
- Only elements on the opposite sides of the periodic table will form ionic compounds
16
Q
Which groups of elements are most likely to form ions?
A
Groups 1, 2, 6 and 7
17
Q
Which groups are metals?
A
Groups 1 and 2 (lose electrons and become positive)
18
Q
Which groups are non-metals?
A
Groups 6 and 7 (gain electrons and become negative)
19
Q
What should you remember when working out the formula of an ionic compound?
A
- The overall charge of any compound is 0
20
Q
What is covalent bonding?
A
When atoms share electrons and both atoms end up with a full outer shell. This gives them the electronic structure of a noble gas.
21
Q
What is a noble gas?
A
They are chemically unreactive gases and are found in Group 0 in the periodic table
22
Q
How are covalent bonds shown?
A
With line between the two atoms
E.g. H-H
23
Q
What do the atoms form during the process of covalent bonding?
A
The atoms form strong covalent bonds that form small molecules of several atoms
24
Q
What are the forces of attraction like between the small molecules?
A
They are very weak
25
What happens during covalent bonding?
The atoms form very strong covalent bonds to either form simple molecular substances or giant molecular substances
26
What are the forces of attraction like between the small molecules in a simple molecular substance?
They are very weak
27
Why are the melting points and boiling points low in simple molecular substances?
The forces of attraction are very weak so the molecules are easily parted. (the inter-molecular forces get broken down, not the covalent bond itself)
28
What state are simple molecular substances in at room temperature?
Most are either gases or liquids but they can be solids
29
Do the simple molecular substances conduct electricity? Why?
They do not because there are no ions so there is no electrical charge.
30
What are giant covalent structures?
Macromolecules
31
What are giant covalent structures similar to?
Ionic lattice structures, except there are no charged ions
32
How are the atoms bonded together in a macromolecule?
By strong covalent bonds
33
Why are the melting and boiling points high in macromolecules?
Because the forces of attraction between the molecules are strong and do not part easily.
34
Do macromolecules conduct electricity?
No, except for graphite when molten
35
What three substances have giant covalent structures?
Diamond
Graphite
Silicon Dioxide (silica)
36
What are the properties of diamond?
- Each carbon atom forms 4 covalent bonds in a very rigid, giant covalent structure
- This structure makes it the hardest natural substance
37
What are the properties of diamond?
- Each carbon atom forms 4 covalent bonds in a very rigid, giant covalent structure
- This structure makes it the hardest natural substance
38
What are the properties of graphite?
- Each carbon atom forms 3 covalent bonds which creates layers that slide over each other
- The sliding layers makes graphite soft and slippery
- The layers are held together so loosely that they can be rubbed onto paper. This is because there are weak inter-molecular forces between the layers
39
What is so special about graphite?
It is the only non-metal that is a good conductor of heat and electricity. This is because each carbon atom has one delocalised electron that conducts heat and electricity.
40
What are the properties of silicon dioxide (silica)?
- This is what sand is made of
| - Each grain of sand is one giant structure of silicon and oxygen
41
What are the properties of silicon dioxide (silica)?
- This is what sand is made of
| - Each grain of sand is one giant structure of silicon and oxygen
42
What are the properties of all metallic structures?
1. The metallic bonds involve 'free electrons'
| 2. They have delocalised (free) electrons that come from the outer shell of every metal atom in the structure.
43
What do the delocalised electrons do?
1. They are free to move through the whole structure which makes metals good conductors of heat and electricity
2. They also hold atoms in a regular structure because of the strong forces of electrostatic attraction between the positive metal ions and the negative electrons
3. They also allow the layers of atoms to slide over each other, allowing metals to be bent and shaped
44
What is an alloy?
When two or more metals are mixed together to create an alloy with desired properties
45
What happens when creating an alloy?
When a metal is mixed with a pure metal, the new metal atoms distort the layers of metal atoms and free electrons. This makes it difficult for them to slide over the top of each other and makes the harder and stronger than normal metals.
46
What is a smart material?
A material that behaves differently depending on the conditions.
47
Give an example of a smart material and what it does.
Nitinol (shape memory alloy). You can bend and twist it and it will stay that shape. However, when heated, it will go back to its original shape. It is used for dental braces and glass frames.
48
What is a nanoparticle?
A small particle that contains roughly a few hundred atoms. It includes fullerenes. It has very different properties from the 'bulk' chemical that it is made from.
49
What is a fullerene?
Molecules of carbon, shaped like hollow balls/closed tubes. The carbon atoms are arranged in hexagonal rings. Different fullerenes contain different numbers of carbon atoms. Fullerenes can be joined to form nanotubes.
50
What makes carbon nanotubes very strong?
All the covalent bonds
51
What uses do nanotubes have?
1. They have a huge surface area to volume ratio so can help make new industrial catalysts
2. To make sensors to detect one type of molecule
3. To test water purity
4. To make stronger, lighter building materials
5. To make new cosmetics
6. To make nanomedicine- fullerenes are easily absorbed by the body so they could potentially deliver drugs to cells where it is needed.
7. New lubricant coatings
8. To conduct electricity- can be used in tiny electric circuits for computer chips
52
What are polymers?
Very large molecules that are made when many smaller molecules join together in chains, end-to-end. The smaller molecules are called monomers.
53
Give an example of a polymer.
Plastic
54
What determines the properties of plastics?
The forces between the molecule chains that make up the plastic
55
What are the properties of a plastic that has weak forces between the molecules?
1. The individual chains are held together by weak inter molecular forces so they are free to slide over each other
2. There is not cross-linking between chains so they are easy to melt as forces between the chains are easy to overcome
56
What are the properties of a plastic that has strong forces between the molecules?
1. Strong inter molecular forces between polymer chains called cross links.
2. The cross-links hold the chains firmly together
3. Means it is harder to melt as forces between chains are harder to overcome
57
What is LDPE?
Low Density Polythene
58
What is HDPE?
High Density Polythene
59
How is LDPE made?
By heating ethene to about 200 C under high pressure
60
How is HDPE made?
Made at a lower pressure and temperature using a catalyst
61
What can LDPE be used for?
It is flexible so plastic bags and bottles
62
What can HDPE be used for?
It is rigid so used for water tanks and drainpipes
63
What is the Relative Atomic Mass?
How heavy different atoms are compared with the mass of carbon -12.
64
What is the Relative Formula Mass?
The sum of all the relative atomic masses added togther
65
One mole of a substance is equal to what?
Equal to its relative atomic mass.
| E.g. Iron has a relative atomic mass of 56 so one mole of iron is 56g
66
How do you convert between the number of moles and grams?
Number of moles = mass in grams/ relative formula mass
| n = m/Mr
67
How do you work out the concentration of a solution?
C = n/v
c-concentration (mol/dm3)
n-number of moles (mol)
v-volume of solution (dm3)
68
How do you calculate the percentage mass in a compound?
Relative atomic mass/relative formula mass
69
What does working out the percentage yield do?
1. Tells you about the success of an experiment
| 2. Compares actual yield to the predicted yield
70
How do you work out the percentage yield?
actual yield (g)/ predicted yield (g) x 100
71
Why are yields less than 100%?
Some of the atoms get lost on the way
72
How are atoms lost during a reaction?
1. In a reversible reaction, reactants will never be completely converted because the reaction goes both ways. The products are also always reacting together to change back to original reactants which means there will be a lower yield.
2. If you filter a solution, you will always lose a bit of liquid or solid. Some products get lost when they are separated from the reaction mixture
3. There could be some unexpected reactions that use up the reactants, which means that there will not be as much reactant to make product you want.
73
Why is percentage yield important for sustainable development?
- to ensure that we do not use up resources faster than they can be replaced
- to ensure we are using as little energy as possible to create highest product yield possible
- to ensure we are not wasting resources- low yield means wasted chemicals
74
What four things does the rate of reaction depend on?
1. Temperature
2. Concentration (or pressure for gases)
3. Catalyst
4. Surface Area
75
If you increase any of the four things that the rate of reaction depends on what happens?
The rate of reaction increases
76
What is the formula for working out the rate of reaction?
rate of reaction = amount of reactant used or amount of product formed/time
77
What does the formula for working out the rate of reaction do?
Measures how quickly the reactants are used up or how quickly a product(s) are formed.
78
What is paper chromotography?
The separating out of artificial colours by placing paper, with dye on, into a solution and observing how the dye is separated out into different colours.
79
What are the advantages of using a machine (instrumental method) to analyse unknown substances?
- It is very sensitive so it will pick up tiny amounts of substances unlike paper chromotography
- It is fast and tests can be automated
- It is very accurate
80
What is gas chromotography?
The separating out of a mixture of compounds to help identify the substances present.
81
Describe the process of gas chromotography.
1. Gas is used to carry substances through a column of solid material
2. The substance travel through the column at different speeds, so they are separated
3. The time taken to reach the detector is called the retention time, which can be used to identify substances
4. The recorder machine draws out the gas chromotograph- the peaks show the number of different compounds and position of peaks shows the retention time of each substance.
5. The gas chromotography column links to the mass spectrometer (GC-MS) and identifies the substance leaving the column accurately
82
How do you know if the product of a reaction is a precipitate?
The products will cloud the solution
83
Describe the precipitation reaction.
1. A cross or mark is placed under the flask during the reaction.
2. Time how long it takes for cross to disappear. The quicker it disappears, the quicker the rate of reaction.
84
What are the disadvantages of the precipitation reaction?
1. only works when initial solution is see through
| 2, result is subjective-different people may not agree er exact point at which the cross disappeared
85
What three ways can you measure the rate of reaction?
1. Precipitation
2. Change in mass
3. Volume of gas given off
86
Describe how to measure the change in mass.
1. Place flask on mass balance- record initial reading
| 2. Measure how quickly the mass drops during reaction- the quicker it falls, the faster the reaction
87
What are the advantages and disadvantages of measuring the change in mass?
+ easy to plot using results
+ most accurate method of measuring rate of reaction
- releases gases straight into the air
88
Describe how to measure the amount of gas given off.
1. Place gas syringe in flask during reaction to measure gas given off- the more gas given off during time interval, the faster the reaction.
89
What are the advantages and disadvantages of measuring the volume of gas given off?
+ quite accurate
| - if the reaction is to vigorous, the plunger of the gas syringe may be blown out of the end
90
What is the collision theory?
It states that the rate of reaction depends n how often and how hard the particles collide with each other.
The particles must have enough energy to collide with each other successfully in order to react
The more successful collisions, the faster the rate of reaction
91
How does temperature affect the rate of reaction?
- the increase in temperature cause the particles to vibrate more so they have more energy
- the increase in energy will cause the particles to move faster
- if the particles are moving faster there are going to be more frequent and faster collisions
- more frequent collisions means the rate of reaction will increase
92
How does concentration affect the rate of reaction?
- a higher concentration means there will be more particles in between the other molecules in the solution
- if there are more particles, there are going to be more frequent collisions which will increase the rate of reaction
- If the pressure is increased in a gas, the particles are closer together which means there will be more frequent collisions
93
How does the surface area affect the rate of reaction?
- surface area is increased by breaking down the reactant(s) into smaller pieces
- the particles within the solution have more area to work on which causes more frequent collisions. This increases the rate of reaction
94
What is the activation energy?
The minimum amount of energy needed for particles to react
95
What is a catalyst?
A substance that speeds up the reaction, without being changed or used up in the reaction
96
What happens to the reaction when a solid catalyst is used?
It gives the reacting particles something to stick to so it increases the number of successful collisions. This causes the rate of reaction to increase
97
What are the advantages of using a catalyst?
- increases the rate of reaction so it saves money because the power plant does not need to operate for as long
- allows reaction to work at lower temperatures- saves money because it reduces amount of energy needed
- can use catalysts again and again-god for sustainable development
98
What are the disadvantages of using a catalyst?
- expensive to buy
- different reactions use different catalysts- more than one product produce at a power plant means you'l have to buy more catalysts
- they can be 'poisoned' by impurities and stop working so you have to keep the reaction mixture clean
99
What is an exothermic reaction?
A reaction that gives out energy into its surroundings, in the form of heat, which is shown by a rise in temperature
100
What is an endothermic reaction?
A reaction that takes in energy, in the form of heat, form the surroundings, which is shown by a fall in temperature
101
What types of reactions are exothermic?
- Oxidation
| - Neutralisation
102
Give an example of an endothermic reaction.
Thermal decomposition
103
What are the uses of an exothermic reaction?
- hand warmers (use oxidation of iron to generate heat)
| - self heating cans (exothermic reactions between chemicals in base of can)
104
What are the uses of endothermic reactions?
-sports injury packs (take in heat and pack becomes cold)- more convenient than ice pack
105
What is the definition of electrolysis?
The splitting up of an ionic substance by passing electricity through it
106
What is required to conduct electricity in the process of electrolysis?
A liquid called the electrolyte
107
What is in the electrolyte? Why are these important?
Free ions. They are important because they are the thing that conducts electricity and allows the whole thing to work
108
In electrolysis, what does reduction mean?
It is the gain of electrons
109
In electrolysis, what does oxidation mean?
It is the loss of electrons
110
What is the cathode?
The negative electrode involved in electrolysis.
111
What is the anode?
The positive electrode involved in electrolysis.
112
How do you remember which electrode is which?
PANiC
| Positive Anode Negative Cathode
113
How do you remember what oxidation and reduction are?
OIL RIG
Oxidation Is Loss
Reduction Is Gain
114
What are cations?
The positive ions that are attracted to the cathode.
115
What are anions?
The negative ions that are attracted to the anode
116
What happens at the anode?
Oxidation happens because the anions lose their electrons
117
What happens at the cathode?
Reduction happens because the cations gain electrons
118
What are the uses of the products formed in the electrolysis of sodium chloride in an aqueous solution?
Chlorine: used to kill bacteria
Hydrogen: used to make margarine
Sodium hydroxide: used in making paper and soap
119
What ions are added to the solution if an aqueous electrolyte is used during electrolysis?
H+ ions
| OH- ions as well as ions from the compound
120
What happens if there are more than two free ions in the electrolyte? (Usually occurs in an aqueous electrolyte)
At the cathode: if metal ions and H+ ions are present, the metal ions will stay in the solution if the are more reactive than hydrogen. Hydrogen will only be produced if the metal is less reactive than it
At the anode: if there is a halogen (halide) present in the solution then they will form at the anode. However, if there isn't one present oxygen will be formed
121
What do half equations show?
The reactions at the electrodes
122
What is the main thing to remember when doing half equations?
Make sure the number of electrons is the same for both half equations
Balance the equation like normal
123
What is the electrolysis of aluminium used for?
To remove aluminium from its ore
124
What happens after aluminium is mined?
- The main ore of aluminium is bauxite and a white powder is left after mining and purifying
- The white powder is pure aluminium oxide
- The aluminium has to be extracted using electrolysis
125
Why is electrolysis used to remove aluminium from its ore?
- The melting point of aluminium is really high so melting it would be very expensive
126
What happens during the process of the electrolysis of aluminium oxide?
- Aluminium oxide is dissolved in molten cryolite
- This brings the melting point down so it is cheaper and easier
- The electrodes are made of carbon, a good conductor of electricity-anode and carbon lining for cathode.
127
What is formed at the cathode during the electrolysis of aluminium oxide?
Aluminium
128
What is formed at the anode during the electrolysis of aluminium oxide?
Oxygen
129
Why do anodes have to be replaced regularly during the electrolysis of aluminium oxide?
The oxygen reacts with the carbon to form carbon dioxide. This eats away at the anode so they have to be replaced.
130
What is electroplating?
The coating of one metal onto the surface of another through the process of electrolysis.
131
What is the cathode made out of in the process of electroplating?
The metal object that you want to plate
132
What is at the anode during the process of electroplating?
The pure metal that you want to coat the other object with
133
What must the electrolyte contain in order for electroplating to take place?
The electrolyte must contain ions of the plating metal.
134
Why must there be ions present in the electrolyte during them process of electroplating?
Because only those ions can move through the solution so impurities will fall of in the solution.
135
What are the different uses for electroplating?
1. Decoration: it is cheaper and easier to plate a metal object with silver than to make the whole thing out of it
2. Conduction: metals like copper conduct electricity well so they are often used to plate metals for electronic circuits and computers
