Chemistry Flashcards
(116 cards)
0
Q
What’s ionic bonding?
A
The giving or taking of an electron between a metal and a non-metal.
(Ionic compounds are neural since the charges cancel each other out)
1
Q
What’s an isotope?
A
Atoms of the same element but with a different number of neutrons.
They have the same number of protons and electron but a different number of neutrons.
They have the same chemical properties but different physical properties because of their different masses. Some are unstable and radioactive.
2
Q
What’s an ion?
A
An atom or molecule with a net electric charge due to the gaining or losing of one or more electrons.
3
Q
What happens to sodium and chlorine during ionic bondng?
A
Sodium loses an electron and becomes a positive ion and chlorine gains an electron and becomes a negative ion.
4
Q
How do ions bond?
A
One ion is negative and one is positive so they are attracted to each other.
This is called electrostatic attraction and forms an ionic bond.
Ionic compounds are neutral as the charges on the ions cancel each other out.
5
Q
What’s covalent bonding?
A
The sharing of a pair of electrons between a non metal and a non metal
6
Q
What happens with the covalent bonding of hydrogen?
A
As hydrogen has 1 (/2) electron on its (first) outer shell, it needs 1 more electron for a full shell so they bond together and share a pair of electrons.
7
Q
What happens with the covalent bonding of oxygen?
A
As oxygen has 6 electrons on its outer shell, there has to be a double covalent bond as it wouldn’t be able to share a pair of electrons and have a full outer shell.
8
Q
Common properties of metals
A
Good conductor of heat (delocalised electrons) Good conductor of electricity (delocalised electrons) Solid at room temp (except mercury) Sonorous Ductile Malleable High melting and boiling point Shiny High density Have free, delocalised electrons
9
Q
Why are metals malleable?
A
The atoms are the same size and arranged in layers so the layers can easily slide over each other.
10
Q
Why do metals have high melting points?
A
Because there is high electrostatic attraction between the metal ions and electrons so lots of energy is needed to overcome the attraction and melt the metal.
11
Q
How does a calcium atom change to a calcium ion with a 2+ charge?
A
It loses two of its electrons and becomes positively charged.
12
Q
What type of structure is graphite and diamond and why do they have high melting points?
A
Giant covalent
Because they have strong intramolecular bonds which require lots of energy to break.
13
Q
What are hydrocarbons?
A
A compound of hydrogen and carbon from crude oil.
14
Q
What are the simplest alkane hydrocarbons?
A
Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10 Pentane C5H12
15
Q
What’s the formula for alkanes?
A
They are saturated and have the formula CnH2n+2
16
Q
What are the simplest alkene hydrocarbons?
A
Ethene C2H4
Propene C3H6
Butene C4H8
Pentane C5H10
17
Q
What’s a polymer?
A
Really long chains of molecules (monomers)
18
Q
What are monomers?
A
A molecule which can bond to form long chains of polymers.
19
Q
What’s bad about polymers (plastics)
A
Made from crude oil - limited
Incineration emits toxic gasses
Landfills take up space and lots of time to decompose
20
Q
What are the 2 types of plastic?
A
Thermosoftening / thermoplastic:
Can be heated and remoulded
Have weak intermolecular forces which break when heated - these allow the polymer chains to slide over each other.
Made up of individual polymer chains that are tangled together which when heated become soft and hard and is one called
Thermosetting:
Rigid and have a high melting point
Can’t be remoulded
Have strong cross links between polymers which don’t break when heated
21
Q
What are the 4 things which affect the rate of a reaction?
A
Temperature
Surface area
Concentration
Catalysts.
22
Q
How does temperature affect the rate of a reaction?
A
The higher the temperature, the faster the rate of reaction.
It gives the particles more energy so they move around faster, therefore colliding more often in the same amount of time, meaning the reaction occurs faster.
23
Q
How was concentration affect the rate of reaction?
A
The higher the concentration, the faster the rate of reaction.
If there is an increase in concentration, this means there are more particles in the same volume of the substance therefore there will be more, successful collisions and a higher rate of reaction.
24
How does surface area affect the rate of reaction?
The large the surface area (smaller the surface area) the faster the rate of reaction.
You increase the surface area each time the object is cut smaller so small substances react faster. This is because, as smaller objects has larger surface areas, there are more atoms exposed on these surfaces, ready to react.
25
What's a catalyst?
A substance that speeds up the rate of reaction without actually being used up in the reaction itself.
They never produce more product, just the same amount more quickly.
Most lower the reactions activation energy (Ea) meaning they require less energy (minimum energy required).
26
What gas is given off when calcium carbonate reacts with hydrochloric acid and how can the volume of gas given off be measured?
Carbon dioxide
1) measure the loss in mass on a balance as the reaction happens.
2) collect the gas in a measuring cylinder filled with water or in a gas syringe.
27
When are reactions usually at their fastest?
At the start.
28
Which would react fastest in dilute acid, the same mass of iron nails, iron wool or iron filings?
Iron filings
29
If 5g of marble chips were reacted with the same amount of acid at 30°C and 40°C, would you get more gas given off by the end of the reaction at 30°C or 40°C
The same volume of gas (but quicker at 40°C)
30
What are our everyday catalysts?
Nickel - production of margarine (hydrogenation)
Iron - production of ammonia from nitrogen and hydrogen
Platinum - in car catalytic converters, converting carbon monoxide and nitrogen oxide onto CO2 and nitrogen.
31
Why are catalysts used in industry?
Products can be made quicker, saving time and money.
| Catalysts also reduce the need for high temperatures, reduce pollution and save fuel.
32
What are the equations for the rate of reaction?
Amount of reactant used / time
Or
Amount of product formed / time
The gradient on a graph can also show the rate of reaction.
33
What is the collision theory?
The theory stating that reactions can only happen if particles collide (with enough energy to create new substances). The minimum energy needed is called the activation energy.
34
How does the pressure of gas affect the rate of the reaction?
The increase of the pressure of gas increases thw frequency of collisions and so increases the rate of reaction.
35
What's an exothermic reaction?
A reaction in which energy is transferred from the reacting substances to their surroundings.
(Providing heat)
Examples of exothermic reactions include combustion and oxidation.
E.g. Reusable hand warmer (less waste but has to be heated again and has a slower reaction)l
36
What's an endothermic reaction?
A reaction in which energy is transferred to the reacting substances from their surroundings.
Energy is taken from the surroundings.
(Making it colder)
E.g. Instant cold packs (can be stored easily but can only be used once).
37
Explain metallic bonding
When metal atoms pack together, the electrons in the highest energy level (the outer electrons) delocalise and can move freely between atoms. This produces a lattice of positive ions in a 'sea' of moving electrons.
The delocalised electrons strongly attract the positive ions and hold the giant structure together.
38
Why do ionic solids have high melting points?
Because ionic compounds have giant structures in which many strong electrostatic forces hold the ions together. This means they're solid at room temperature and need a lot of energy to overcome the ionic bonds.
39
Why can ionic substances conduct electricity when molten or dissolved in water?
Their ions can move freely and carry charge through the liquid.
40
What are simple molecules?
Atoms in a molecule have strong covalent bonds which act between the atoms in the molecule so simple molecules have little attraction for each other.
Substances which have low melting and boiling points and have no overall charge so don't conduct electricity.
41
What are intermolecular forces?
Weak forces of attraction between molecules.
| Larger molecules have stronger attractions so may be liquids at room temperature.
42
Why do giant covalently bonded structures have high melting points?
They have strong bonds which need lots of energy to break down.
43
What's diamond?
A giant covalent structure and form of car in that's covalently bonded to three other carbon atoms, making it hard and transparent.
44
What's graphite?
Another (giant covalently structured) form of carbon where the carbon atoms form layers that can slide overt each other. It's atoms are bonded to 3 other carbon atoms.
It can conduct electricity because of the delocalised electrons in its structure.
45
How do we measure the rate of reaction?
Rate = amount of reactant used / time
Or
Rate = amount of product formed / time
46
What's activation energy?
Activation energy is the least amount of energy for the reaction to occur.
47
What do group 1 metals react with?
Water and oxygen.
| The further down the periodic table, the more reactive the element.
48
What are group 7 elements?
Halogens which decrease in reactivity the further down the table they go.
When combined with other elements, it becomes safe and can be used for plastic, non stick pans, antiseptic, toothpaste etc.
Fluorine is more reactive than iodine as the outer shell is much closer to the nucleus therefore there is a greater force of attraction between the nucleus and the electron being gained.
When becoming negative, it becomes a halide ion e.g. Fluoride.
49
What's displacement?
When a more reactive element boots out and displaces the less reactive element e.g.
Chlorine + potassium bromide -> potassium chloride and bromine.
50
What's oxidisation and reduction?
```
Oxidisation
Is
Loss of e-
Reduction
Is
Gain of e-
```
51
How are ionic compounds structured?
Ionic compounds are held together by strong forces between the oppositely charged ions, known as ionic bonding. (There are strong electrostatic forces of attraction in all directions so each ion in the giant structure or lattice is surrounded by ions with the opposite charge which holds it firmly in place)
The ions form a giant lattice or structure. The strong forces of attraction act throughout the lattice.
We can represent atoms and ions using dot and cross diagrams.
52
How are covalent bonds formed?
When 2 atoms share a pair of electrons.
The electrons in the highest energy level are delocalised.
53
Why can graphite conduct electricity?
Because of the delocalised electrons in its structure.
54
What are fullerenes?
Large molecules formed from hexagonal rings of carbon atoms.
The rings join together to form cage-like shapes with different numbers of carbon atoms, some of which are nano-sized.
Scientists are finding many applications for fullerenes including drug delivery to the body, lubricants, catalysts and reinforcing materials.
55
What's a shape memory alloy?
An alloy which can return to its original shape after a change in environmental conditions e.g. After heating.
56
What are alloys?
Alloys are mixtures of metals and are harder than pure metals because the layers in the structure are distorted.
57
Why do LD and HD poly(ethene) have different properties?
Low density and high density poly ethene are made using different catalysts and different reaction conditions.
HD poly ethene has a higher softening temperature and is stronger than LD.
58
What do the properties of polymers depend on?
They depend on the monomers used to make them.
| Changing the reaction conditions can also change the properties of polymers.
59
What's nano science?
The study of small particles that are between 1 and 100 nanometers in size.
60
What are nano particles?
A nanometer is one billionth of a metre - nano particles are a few nano metres in size.
Their very small sizes gives them very large surface areas and new properties useful for materials.
Nano technology uses such particles as highly selective sensors, very efficient catalysts, coatings, cosmetics like sun cream and deodorants and construction materials.
If they're used more and more, there will be a greater risk of them finding a way into the air and our bodies which may have unpredictable consequences for our health and the environment and so more research must be done.
61
What is a relative atomic mass?
| A r
Since atoms are too small to weigh, we use their relative atomic masses in calculations.
Represented as Ar, they are often shown in periodic tables.
The relative atomic mass of an element in grams is called one mole of atoms of the elements.
The relative atomic mass of an element is an average value for the isotopes of an element.
We use an atom of 12/6 C as the standard atom and compare masses of all other atoms to this.
often the same number as the mass number of the main isotope of the element.
62
What is the mass of one mole of sodium atoms?
23g
Sodium's relative atomic mass is 23.
63
What's the relative formula mass?
| M r
The mass of a compound or molecule.
| The M r of a substance is found by adding up the relative atomic masses of the atoms in its formula.
64
Calculate the M r (relative formula mass) of calcium chloride:
CaCl2
First friend the relative atomic mass of each atom:
Ar of Ca = 40 Ar of Cl = 35.5
So the M r =
40 + (2 * 35.5)
= 111
65
What's a mole?
The amount of substance in the relative atomic or or formula mass of a substance in grams.
The relative formula mass of a substance is called one mole of that substance.
Using moles of substances is useful when we need to work out how much of a substance reacts or how much product we will get.
66
Calculate the M r of sodium sulphate:
| Na2SO4
First find the A r of each element
Ar of Na = 23
Ar of S = 32
Ar of O = 16
(2 * 23) + 32 + (4 * 16) =
46 + 32 + 64 = 142
67
What is the mass of one mole of sodium hydroxide:
| NaOH
Fist find the A r of the elements:
Na = 23
O = 16
H = 1
So one mole of NaOH = 23 + 16 + 1 = 40g
68
What is the mass of one mole of magnesium carbonate:
| MgCO3
First find the Ar of the substances:
Mg = 24
C = 12
0 = 16
So one mole of MgCO3 = 24 + 12 + (3 * 16) = 84g
69
How can we calculate the percentage of any element in a compound?
From the formula of the compound.
The relative atomic masses of the elements in a compound can be used to work out its percentage composition.
Divide the relative atomic mass (A r) of the element by the relative formula mass (M r) of the compound then multiply the answer by 100 to convert it to a percentage.
70
What is the percentage of carbon in CO2?
First find the A r of the elements:
Carbon = 12
Oxygen = 16
Then find the M r of the compound:
12 + (2 * 16) = 44
Then find the A r (of carbon) / the M r =
12 / 44 = 0.273
Then multiply by 100 to convert it to a percentage:
= 27.3%
71
What's the percentage of carbon in methane?
First find the A r of the elements:
Carbon = 12
Hydrogen = 1
Then find the M r of the compound:
12 + (4 * 1) = 16
Then find the A r (of carbon) / the M r =
12 / 16 = 0.75
Then multiply by 100 to convert it to a percentage:
= 75%
72
How do you work out the formula of a compound from its percentage composition?
What is the empirical formula?
The empirical formula is the simplest ratio of the atoms or ions in a compound.
It's the formula used for ionic compounds, but for covalent compounds it's not always the same as the molecular formula.
For example, the molecular formula of ethane is C2H6 but it's empirical formula is CH3.
We can calculate the empirical formula of a compound from its percentage composition:
Divide the mass of each element (in 100g of the compound) by it's A r to give the ratio of the atoms.
Then convert this to its simplest whole number ratio. (Divide by the smallest result)
73
What is the empirical formula of the hydrocarbon that contains 80% carbon?
First, find the mass in 100g of the compound:
Carbon = 80 Hydrogen = 20
Then divide the mass within 100g (^) by its relative atomic mass for the ratio of atoms (mass / A r) :
Carbon = 80 / 12 = 6.67 Hydrogen = 20 / 1 = 20
Then convert this to the simplest whole number ratio (divide by the smallest answer) :
Carbon = 6.67 / 6.67 = 1 Hydrogen = 20 / 6.67 = 3
Empirical formula = 1 carbon & 3 hydrogen
= CH3
74
What is the empirical formula of the compound that contains 70% iron and 30% oxygen?
First find the mass of the elements in 100g of the compound:
Iron = 70 Oxygen = 30
Then divide this by their A r:
Iron = 70 / 56 = 1.25 Oxygen = 30 / 16 = 1.875
Then find the simplest ratio of atoms (divide by the smallest):
Fe = 1.25 / 1.25 = 1 O = 1.875 / 1.25 = 1.5
(Multiply by 2 to make it whole numbers)
1:1.5 = 2:3
Empirical formula = Fe2O3
75
Why do we use balanced symbol equations?
They tell us the number of moles of substances involved in a chemical reaction.
We use them to calculate the masses of reactant and products in a chemical reaction.
76
How do you calculate masses from chemical equations?
Chemical equations show the reactants and products of a reaction. When they are balanced they show the amount of atoms, molecules or ions in the reaction.
E.g. 2Mg + O2 -> 2MgO shows that two atoms of magnesium react with one molecule of oxygen to form two magnesium ions and two oxide ions.
If we work in moles, the equation tells us that two moles of magnesium atoms react with one mole of oxygen molecules to produce two moles of magnesium oxide.
This means that 48 g of magnesium reacts with 32 g of oxygen to give 80 g of magnesium oxide. (Ar of Mg = 24, Ar of O = 16).
Alternatively if we work in relative masses from the equation: (2 * Ar of Mg) + (2 * Ar of O) gives (2 Mr of MgO)
Converting this to grams, it becomes: (2 * 24g) + (2 * 16g) gives 2 * 40g MgO
OR 48g Mg + 32g O gives 80g MgO (which is the same as using moles).
If we have 5 g of magnesium we can work out the mass of magnesium oxide it will produce using ratios: 1g Mg will produce 80 / 48g MgO.
So 5g MgO will produce 5 * 80 / 48g MgO = 8.33g of MgO.
If we use moles, the calculation can be done like this:
1 mole of Mg produces 1 mole of MgO
5g Mg = 5 / 24 mole of magnesium an so it will produce 5/24 mole MgO.
The mass of 5/24 mole MgO = 5/24 * 40 = 8.33g of MgO.
77
Calculate the mass of calcium oxide that can be made from 10 g of calcium carbonate in the reaction:
CaCO3 -> CaO + CO3
First find the Ar of the elements:
Ca = 40
O = 16
C = 12
40+12+48 = 100
100g -> 56g + 44g
CaCO3 -> CaO + CO2
We need to find the mass of CaO made from 10g of CaCO3:
1 mole of CaCO3 gives 1 mole of CaO
OR
100g of CaCO3 gives 56g CaO.
So
10g of CaCO3 gives (10 / 100) * 56
= 5.6g
78
What's the yield of a chemical reaction?
The yield of a chemical process is how much you actually make.
The percentage yield compares the amount made with the maximum amount that could be made, calculated as a percentage.
It is important to maximise yield and minimise energy wasted to conserve the Earths limited sources and reduce pollution.
79
How do you calculate percentage yield?
Percentage yield = (amount of product collected / maximum amount of product possible) * 100
The maximum amount of product possible is calculated from the balanced equation for the reaction.
Four example a student collected 2.3 g of magnesium oxide from 2.0 g of magnesium.
Theoretically 2Mg + O2 -> 2MgO so 48g of Mg should give 80g MgO.
And so 2g of Mg should give 2 * 80/48 = 3.33g MgO.
OR
(Ar of Mg = 24 [2MgO = 48] so instead of 2 * 80/48, 24 / 2g = 12 so 40 / 12 = 3.33g)
Percentage yield = (2.3/3.33) * 100 = 69%
80
A student made 4.4g of calcium oxide from 4.0g of calcium. Calculate the percentage yield.
2Ca + O2 -> 2CaO
Ar: Ca = 40 O = 16
80g Ca + 32g O -> 112g CaO
4g Ca -> 5.6g CaO
80 / 4 = 20
SO
112 / 20 = 5.6
P.Y. = (4.4 / 5.6) * 100
=78.6%
81
Why isn't it usually possible to get 100% yield from a chemical reaction?
Reactions may not go to completion, other reactions may happen and some product may be lost when it's separated to collected from the apparatus.
82
What is a reversible reaction?
When the products of a reaction can react to make the original reactants.
It's represented by two arrows, one in either direction ()
Reversible reactions are always endothermic in one direction and exothermic in the other.
83
What is chemical analysis?
It's used to find any food additives.
| Methods include paper chromatography and mass spectrometry.
84
How does paper chromatography work to analyse artificial colours in foods?
A spot of colour is put onto paper and a solvent is allowed to move through the paper.
The colours move different distances depending on their solubility.
85
What are the modern instrumental methods of substance analysis and how do they work?
Gas chromatography linked to a mass spectrometer
Samples for analysis are usually mixtures which need to be separated to identify the compounds.
In gas chromatography, the mixture is carried by gas through a long column packed with particles of a solid.
Since individual compounds travel at different speeds through the column, they come out at different times - the amount leaving at different times is recorded against time and shows the number of compounds in the mixture plus their retention times.
The times are then compared to identify the various compounds.
The output from the gas chromatography column can be linked directly to a mass spectrometer (GC-MS) which gives further data.
(Compounds are separated from the mixture using gas chromatography then identified by a mass spectrometer.)
86
What else can a mass spectrometer be used for?
Giving the relative molecular mass of a compound.
For an individual compound, the peak with the largest mass corresponds to an ion with just one electron removed. The peak is known as the molecular ion peak and is furthest to the right on a mass spectrum.
It finds the Mr (relative molecular mass) from its molecular ion peak.
87
What are the two areas of research which offer possibilities for new or better catalysts?
Nano science (highly efficient) and enzymes (work at ordinary temp, reducing energy usage).
Common transition metal catalyst may not always be effective as they can be expensive or toxic.
88
What does anhydrous mean?
A substance which doesn't contain water.
89
What are acids, alkalis and bases?
Acids are substances that produce hydrogen H+ when they're added to water and have a pH less than 7.
Bases react with acids and neutralise them.
Alkalis are bases that dissolve in water to make alkaline solutions. They produce hydroxide ions in the solution and have a pH greater than 7.
90
What happens when acids react with metals?
They produce a salt and hydrogen gas
acid + metal -> a salt + hydrogen
Acids will react with metals greater than hydrogen in the reactivity series however the reactions of acids with very reactive metals like sodium and potassium are too violent.
91
What happens when an acid reacts with a base?
Metal oxides and metal hydroxides are bases.
When an acid reacts with a base, it produces a salt and water.
acid + base -> a salt + water
92
Why do we need excess of the base when making salt?
To use up or neutralise all of the acid.
93
Name the products when:
Nitric acid reacts with magnesium
Hydrochloric acid reacts with copper hydroxide
a) magnesium nitrate + hydrogen (acid and metal makes hydrogen)
b) copper chloride + water (acid and base makes water)
94
How can we make soluble salts?
By reacting an acid with an alkali
acid + alkali -> salt + water
An indicator can be used to show when the reaction is complete since there's no visible change.
Water is produced in every neutralisation reaction
(Equation for neutralisation between any acid and alkali is:
H+ (aq) + OH- (aq) -> H2O (l)
95
How can we make insoluble salts?
By mixing solutions of solvable salts that have ions needed.
E.g. We can make lead iodide by mixing solutions of lead nitrate and potassium iodide.
The lead forms a precipitate that can be filtered from the solution, washed and dried.
96
Zinc carbonate is insoluble in water. What would happen when sodium carbonate solution is added to the zinc sulphate solution?
Zinc carbonate would be formed as a precipitate or solid and the sodium sulphate would remain in the solution
97
What's a precipitate?
An insoluble solid formed by a reaction taking place in a solution.
98
What's electrolysis?
The process which uses electricity to break down ionic compounds into elements.
This occurs when electricity is passed through a molten ionic compound or a solution containing ions.
99
Why must the ionic compound be molten or solution for electrolysis to take place?
So that then, their ions are free to move to the electrodes.
100
What is the electrolyte?
The substance that is broken down during electrolysis.
101
How does electrolysis work?
It is a large electrical circuit which has two electrodes that make contact with the electrolyte.
The electrodes are made of inert, unreactive substances which do not react with the products.
The ions of the electrolyte move to the electrodes where they are discharged to produce elements.
Positively charged ions are attracted to the negative electrode (cathode) where they form metals or hydrogen, depending on the ions in the electrolyte.
Negatively charged ions are attached to the positive electrode (anode) where they lose their charge to form non-metallic elements.
E.g. When molten lead bromide is electrolysed, lead is produced at the negative electrode and bromine is produced at the positive electrode.
102
What changes occur at the electrodes during electrolysis?
When positively charged ions reach the negative electrode, they gain electrons to become neutral atoms so the positive ions are reduced.
At the positive electrode, negative ions lose electrons to become neutral atoms so become oxidised.
103
What gases are produced during electrolysis?
When solutions are electrolysed:
Oxygen gas is produced at the positive electrode (unless the solution contains halide ions - then a halogen will be produced).
Hydrogen gas is produced at the negative electrode (unless the solution contains ions of a metal that is less reactive than hydrogen).
104
What are half equations?
We represent the changes at electrodes by using half equations.
E.g. The half equations for lead bromide are:
At the cathode: Pb 2+ + 2 e- -> Pb
At the anode: 2Br- -> Br2 + 2e-
105
What's oxidation and reduction?
Oxidation is loss of electrons
| Reduction is gain of electrons
106
How is aluminium extracted?
It's more reactive than carbon so must be extracted from its ore by electrolysis. The aluminium oxide ore must be purified then melted to be electrolysed.
It melts at over 2000'C, needing lots of energy, so another ionic compound called cryolite is added so that the mixture melts at about 850'C
Aluminium ions are reduced to aluminium atoms by gaining electrons at the negative electrode.
Oxide ions are oxidised to form oxygen atoms by losing electrons and the oxygen atoms form oxygen molecules at the positive electrode.
107
What is brine and what are the products gathered from its electrolysis?
A solution of sodium chloride water.
We get chlorine gas (anode) , hydrogen gas (cathode) and a sodium hydroxide solution.
These products are important for industry e.g.
Chlorine kills bacteria
Hydrogen for hydrochloric acid and margerine
Sodium for soaps.
108
What is electroplating?
Electroplating is using electrolysis to put a thin coating of a metal onto an object.
Gold silver and chromium plated are often used.
```
Reasons for this include:
To make things look more attractive
protect from corrosion
increase the hardness of the surface
reduce costs by using a thin-layer
```
The object to be electroplated is made the negative electrode in an electrolysis cell. The plating metal is made the positive electrode. The electrolyte contains ions of the plating metal.
For electroplating the positive electrode is not inert - it produces ions of the metal used to plate the object.
109
What is a shape memory alloy?
Alloy/mixture of metals which can be bent or deformed into a different shape however when heated they return back to their original shape
110
How are polymers bonded?
Is the most softening polymers the forces between the polymer chains are weak
When we heat the polymer, it's weak intermolecular forces are broken and the polymer becomes soft
When the polymer cools down the intermolecular forces bring the polymer molecules back together so it hardens again
111
How is energy transferred in a reversible reaction?
The amount of energy released when the reaction goes in one direction is exactly equal to the energy absorbed when the reaction goes in opposite direction
112
Explain how electricity is conducted in a metal.
Include a description of the structure and bonding of a metal.
- giant structure / lattice / layers / close packed
- made up of atoms / positive ions
- with delocalized / free electrons
- so electrons can move / flow through the metal
113
Banks keep coins in poly(ethene) bags.
These bags are made from low density poly(ethene).
High density poly(ethene) can also be made from the same monomer.
How can the same reaction produce two different products?
any one from:
• different conditions
• different catalyst
• different pressure
• different temperature
114
Give two reasons why instrumental methods of analysis are used to detect impurities in metals:
any two from:
• accurate
• sensitive
• rapid
• small sample
115
Describe the structure and bonding in sodium chloride:
- lattice / giant structure
- ionic or (contains) ions
- Na+ and Cl-
- electrostatic attraction
