CHEMISTRY PART 1 and 2 Flashcards Preview

AQA ADDITIONAL SCIENCE > CHEMISTRY PART 1 and 2 > Flashcards

Flashcards in CHEMISTRY PART 1 and 2 Deck (223):
1

What is the mass number (top)?

Total number of protons and neutrons

2

What is the atomic number (bottom)?

Total number of protons

3

How do you work out the number of neutrons?

Mass number (top) subtract the atomic number (bottom)

4

How do you work out the number of electrons?

They are equal to the number of protons (atomic number)

5

What is the mass of a proton?

1

6

What is the mass of an electron?

Very small

7

What is the mass of a neutron?

1

8

What is the charge of an electron?

Negative (-1)

9

What is the charge of a proton?

Positive (+1)

10

What is the charge of a neutron?

Neutral (0)

11

What are compounds?

When atoms of two or more elements are chemically combined together

12

What is an isotope?

Different atomic forms of the same element which have the SAME number of PROTONS but a DIFFERENT number of NEUTRONS

13

Isotopes have different ... numbers

Mass (top)

14

When are ions formed?

When there is a full outer shell of electrons

15

Ionic compounds always have ...

Giant ionic lattices

16

How are the ions arranged in a regular lattice?

The ions are closely packed

17

Ionic bonding is the ... of electrons

Transferring

18

Ionic bonding takes place between which materials?

Metals and non metals

19

Why are there strong electrostatic forces of attraction between ions?

The opposite charges between the ions attract to each other

20

Why are salt crystals in a cuboid shape?

The single crystal of sodium chloride is one giant ionic lattice

21

Why do ionic compounds have a high MP and BP?

It takes a large amount of energy to overcome the electrostatic forces of attraction

22

When can an ionic substance conduct electricity?

When they melt, and their ions are free to move and carry the charge

23

Elements most likely to form ions are in groups

1
2
6
7

24

Ions have the electronic structure of a...

Noble gas

25

What happens in the ionic bonding of sodium chloride?

The single electron on Sodium's outer shell transfers to become the 8th electron of Chlorine's outer shell. Sodium becomes positively charged, Chlorine becomes negatively charged.
Na+
Cl-
Final product - NaCl

26

What happens in the ionic bonding of magnesium oxide?

The two electrons from Magnesium outer shell transfer to Oxygen's outer shell that would've had 6 electrons. Magnesium becomes positively charged, oxygen becomes negatively charged.
Mg2+
02-
Final product - MgO

27

What happens in the ionic bonding of calcium chloride?

Calcium has two elections on its outer shell. Each goes to a chlorine atom which gain a single electron to complete the full outer shell. The chlorine's become negatively charged, and the calcium becomes positively charged.
Ca2+
Cl-
Cl-
Final product - CaCl2

28

What is covalent bonding?

The sharing of electrons within a compound to achieve a full outer shell

29

Covalent bonding occurs with ...

2 non metals

30

Covalent bonds have a ... MP and BP

Low

31

Why do covalent bonds have low MP and BP?

The covalent bonds are strong but the intermolecular forces between the molecules are weak

32

How can you overcome the weak intermolecular forces in covalent bonds?

Boiling or melting the substances

33

Why can covalent bonds not conduct electricity?

They have no overall charge
There are no charge carriers (free electrons/free ions)

34

Examples of simple covalent bonded molecules (4)

Hydrogen
Oxygen
Methane
Chlorine

35

Boiling and melting points can depend on the...

Size and the shape of a molecule

36

Why does CH4 have a lower BP than CO2?

As the molecules cannot get as near to one another

37

What happens in the covalent bonding of Hydrogen?

Hydrogen have one electron and only require one more for a full outer shell.
Therefore they overlap to share two electrons between both.

38

What happens in the covalent bonding of chlorine?

Chlorine atoms have 7 electrons on their outer shell.
Therefore for the bonding of two chlorine atoms, they share their seventh electron where they overlap.

39

What happens in the covalent bonding of methane?

Carbon has four electrons on its outer shell.
Therefore it forms four covalent bonds with four hydrogen atoms.
Within the overlap there is one electron from hydrogen and one from chlorine (2 in total)
So chlorine has 8 electrons in total and all the hydrogens have a full outer shell too.

40

What happens in the covalent bonding of hydrogen chloride?

Hydrogen and chlorine both require only one more electron for a full outer shell.
Therefore, they share two electrons within the one overlap.

41

What happens in the covalent bonding of ammonia?

Nitrogen has 5 electrons on its outer shell. The final 3 of the 5 each form a covalent bond with a hydrogen atom.
Therefore, they all have a full outer shell.

42

What happens in the covalent bonding of water?

Oxygen has 6 electrons on its outer shell. It bonds with 2 hydrogen atoms.
Therefore there are two electrons in the overlap.

43

What happens in the covalent bonding of oxygen?

Both oxygen atoms have 6 electrons on its outer shell.
Two electrons from each are shared in the overlap (4 in total) to create a full outer shell.
Therefore, a double covalent bond is formed.

44

Most molecular substances are ... at room temperature

Gases and liquids... although they CAN be solids

45

What are macromolecules?

Giant covalent structures or lagged covalent bonded molecules

46

General features of macromolecules

No charged ions
Do not conduct electricity even when molten (except graphite)
High MP and BP
Bonded by strong covalent bonds

47

Examples of macromolecules (3)

Diamond
Graphite
Silicon dioxide (silica)

48

Explain the features of diamond

Made up carbon
Each carbon atoms forms four covalent bonds with other carbon atoms
Rigid structure
Hardest natural substance
Used for drill tips

49

Explain the features of graphite

Each carbon atoms forms 3 covalent bonds - creating layers
The bonds are strong but intermolecular forces between the layers are weak
Layers slide which is how a pencil works
Soft and slippery
Only non metal that conducts heat electricity as each carbon atom has one free/delocalised electron

50

Properties of metals (7)

Conduct heat
Conduct electricity
Sonorous
Ductile
High MP and BP
Hard
Malleable

51

Define sonorous

Makes a ringing sound when hit

52

Define malleable

Can be hammered/ bent into different shapes

53

Define ductile

Can be drawn into wires

54

Metal properties are due to ...

Free electrons

55

Where do free electrons in metals come from?

The outer shell of every atom in the giant structure

56

How do free electrons help the structure of a metal?

They hold the atoms together as the strong electrostatic forces attract the positive metal ions and negative metal ions

57

Why do metals have a high MP and BP?

The free electrons are negatively charged and therefore attract the positive ions by electrostatic forces.
The strong forces are difficult to overcome, hence the high BP and MP

58

Why can metals conduct electricity and heat?

The free ions are free to move and carry the charge

59

Why are metals malleable?

The position of ions can change because of the movement of free electrons
The layers of atoms can slide over each other allowing it to be bent/shaped

60

What are alloys?

A mixture of 2 or more metals, usually to create a material with more desirable properties

61

Why are alloys harder than pure metals?

Different sized elements have different sized atoms
Therefore a mixture of the two, distorts the the regular arrangement
This makes it difficult for the atoms to slide over each other
Therefor they are harder than pure metals

62

Examples of alloys (3)

Amalgam, mostly mercury, used in dental fillings
Brass, mostly copper and zinc, used in hinges/electrical plugs
Solder, mostly lead and tin, used to join metals

63

Smart alloys

Behave different/have unusual properties depending on conditions e.g. Temperature

64

Example of a smart alloy

Nitinol (nickel and titanium)
Metal alloy
If bent out of shape, it returns when heated or an electric current is passed through it
Useful for glasses frames and some dental braces

65

Fullerenes examples

Buckminister fullerene
Nanotube

66

Properties/ uses of buckminister fullerene

Hexagon shape, connected to make a sphere
Uses included drug delivery in body, lubricants and catalysts

67

Properties/ uses of nanotube

Light
Potentially strong
Tube structure of carbon in hexagons
Uses include reinforcing materials e.g tennis racket

68

Features of nanoparticles

VERY small 1-100nm across
Include fullerenes
Contain a few hundred atoms
Different properties
Very large surface area to volume ratio

69

Why do fullerenes make a good conductor?

They have a large surface area to volume ratio (for the amount of material, the surface area is huge)

70

Uses of nanoparticles

New industrial catalysts
Highly specific sensors
Stronger, lighter building materials
Sun tan/deodorant
Nanomedicine e.g. Drug delivery
Lubricant coatings
Electric circuits for computer chips

71

What determines the properties of plastics?

The forces between the molecules

72

What causes the atoms to be held together in long chains (in plastics)?

The strong covalent bonds

73

How do weak forces affect the chains in polymers?

They are held together by weak intermolecular forces and therefore become more tangled
They are free to slide over each other

74

How strong forces affect the chains in polymers?

They have stronger intermolecular forces called crosslinks
This holds the chains firmly together

75

What does LDPE stand for?

Low density poly(ethene)

76

What does HDPE stand for?

High density poly(ethene)

77

Why do LDPE and HDPE have different properties?

They are made under different conditions

78

Properties of LDPE

Polymers have side branches that disrupt the regular arrangement so it has a LOW density
Forces of attraction are weak as chains are further apart
More transparent and flexible then HDPE

79

Properties of HDPE

Molecules line up so the density is HIGH
Molecules are held together strongly so it has a high melting point
Forces of attraction are strong
Very few, if any side branches
Stiff, rigid and strong

80

What is LDPE used for?

Bags and bottles

81

What is HDPE used for?

Water tanks and drain pipes

82

How is LDPE made?

Hearing ethene to 100-300 degrees under high pressure
Oxygen used in reaction

83

How is HDPE made?

Made at a lower temperature and pressure with a aluminium based metal oxide as a catalyst

84

Thermosoftening polymers properties

No regular structure
Forces between chains are easy to overcome
Easy to melt
Can be remelted and remoulded as many times as you like

85

Thermosetting polymers properties

They have cross links which hold it together in a solid structure
Strong covalent bonds
Doesn't soften when heated
Difficult to melt
Cannot be remoulded once heated
Strong, hard and rigid

86

Examples of thermosoftening polymers

Plastic bottles
Containers

87

Examples of thermosetting polymers

Cooking spatulas
Pan handles
Plug sockets

88

Why are thermosoftening polymers easily separated and can melt?

Weak intermolecular forces
Polymers can separate more easily at lower temperatures so les heat is needed to separate the chains

89

Define relative atomic mass

How heavy different atoms are compared with the mass of an atom of carbon 12

90

How can you find the relative atomic mass?

It's the same as the mass number of the element (top number)

91

Define relative formula mass (2)

Relative atomic masses added together
OR
The relative formula mass of a substance, in grams is one mole of that substance.

92

Number of moles formula

Number of moles =
Mass in g of the element/ compound
DIVIDED BY
The relative formula mass of the element/ compound

93

Percentage mass of an element in a compound formula

Percentage mass =
Relative formula mass of element x number of atoms of the element
DIVIDED BY
Relative formula mass of compound
MULTIPLIED BY
100

94

What is the percentage mass of sodium in sodium carbonate?

23 x 2 divided by 106 times 100 equals
43.4%

95

How do you find the empirical formula from masses or percentages? (5)

1. List all elements given
2. Below, write the masses or percentages given
3. Divide each mass or percentage by the relative formula mass (masses added together)
4. Divide both answers by the smallest answer
5. Write out the empirical formula

96

Empirical formula of carbon and oxygen

1. C= 1.2g, O=3.2g
2. C=12, O=16
3. C= 1.2/12=0.1, O=3.2/16=0.2
4. C= 1.2/1.2=1, O=0.2/0.1=2
5. CO2

97

How do you calculate masses in a reaction?

1. Write out the balanced equation
2. Work out the relative formula mass (for the two bits you need)
3. Divide to get one, then multiply to get all (do this on both sides)

98

Percentage yield formula

Percentage yield =
actual yield (grams)
DIVIDED BY
predicted yield (grams)
TIMES BY
100

99

What is a percentage yield?

Tells you the overall success of an experiment
It compares the predicted yield and the actual yield

100

What is yield?

The amount of product you get from a reaction

101

The more reactants you start with, the ... the actual yield

Higher

102

What doesn't yield percentage depend on?

The amount of reactants you started with, because it is a percentage

103

How can the predicted yield of a reaction be calculated?

Using the balanced equation reaction

104

Predicted yield can also be known as the ...

Theoretical yield

105

What percentages are percentage yield in between?

0-100%

106

What does a 100% yield percentage suggest?

You got all the product you expected to get

107

What does a 0% percentage yield suggest?

No reactants were converted into a product, so no product was made

108

Why can you never get a 100% yield percentage?

Some product or reactant will always get lost along the way (including big industrial processes as well as school lab experiments)

109

Why can product and reactants get lost along the way?

1. Reversible reactions
2. Filtration
3. Unexpected reactions

110

How can reversible reactions lead to product/reactant being lost?

Reactants will never be completely converted to products as the reactions goes both ways, which results in a lower yield

111

How can filtration lead to product/reactant being lost?

When you filter a liquid to remove solid parts, you always lose a bit as it may get separated from the reaction mixture

112

How can unexpected reactions lead to product/reactants being lost?

Unexpected reactions may use up reactants, so there is not as much reactants to make the product you want

113

What is a reversible reaction?

Where the products of the reaction can react with themselves to product the original reactants

114

What is an example of a reversible reaction?

Ammonium chloride ammonia + hydrogen chloride

115

What is sustainable development about?

Making sure we don't use resources faster than we can replace them

116

Why is the highest product yield sustainable?

It uses little energy
Resources are saved

117

Why is a low yield not as sustainable?

Chemicals are wasted

118

How can you tell which dye is the most soluble?

It will move furthest up the paper

119

What is paper chromatography used for?

Separating artificial colours such as food colouring (containing one dye or a mixture of dyes)

120

How does paper chromatography work?

- Extract the sample into a cup with water
- Draw a pencil baseline on some filter paper and add spots of the coloured solution
- Add the paper into the water, making sure the pencil like is above the solution
- Different dyes will then form onto the paper

121

What does a chromatogram with four spots suggest?

At least four dyes, not exactly four dyes

122

What is gas chromatography used for?

Separating a mixture of compounds and helping to identify the substances present

123

How does gas chromatography work?

- A carried gas carries substances through a column with solid material
- the substances travel and different speeds so they are separated
- the detector helps to identify the substances
- a recorder then draws a gas chromatograph

124

What is the retention time?

The time it takes for the substances to reach the detector

125

What does the number of peaks in a gas chromatograph show you?

The number of different compounds in the sample

126

What does the position of the peaks in a gas chromatograph show you?

The retention time of each substance

127

What is GC-MS?

When the gas chromatography column is linked to a mass spectrometer.
It identifies the substances leaving the column QUICKY and ACCURATELY

128

How do you work or the relative formula mass of the substances from a GC-MS?

Read it from the molecular ion peak on the graph it draws
(the peak furthest to the right)

129

Advantages of using machines to analyse unknown substances (3)

- sensitive
- fast
- accurate

130

Paper chromatography - summary

Paper -
Mobile phase is liquid
Analyse food dyes
Stationary phase is paper
Easy to do
Difficult to obtain accurate results
Substances travel at different speeds
Analyse mixtures in a solution

131

Gas chromatography - summary

Gas -
Mobile phase is gas
Used to detect alcohol in breath
Stationary phase is a solid packed in a column
Requires special equipment
Gives accurate results
Substances travel at different speeds
Analyse substances in a vapour
Sensitive

132

Example of a slow reaction

The rusting of iron

133

Example of a moderate speed reaction

Metal reacting with an acid

134

Example of a fast reaction

An explosion

135

What does a rate of reaction depend on? (4)

- Temperature
- Concentration (or pressure for gases)
- Catalyst
- Surface area of solid

136

How can the rate of reaction be observed? (2)

How quickly the reacts are used up
How quickly the products are formed

137

Formula to calculate rate of reaction

Rate of reaction=
Amount of reactant used/product formed
DIVIDED BY
time

138

Ways the rate of reaction can be measured (3)

Precipitation
Change in mass (usually a gas given off)
Volume of gas given off

139

How can the rate of reaction be measured precipitation?

This is when the product is a precipitate and makes the solution go cloudy
You can observe a mark in the solution to see how long it takes for it to disappear
The quicker it disappears, the quicker the reaction
People may disagree to when the "mark" disappears

140

How can the rate of reaction be measured by a change in mass?

This can be carried out on a mass balance
As the gas is released, the mass disappearing is measured on the balance
The quicker the reading drops, the faster the reaction
Most accurate
However, the gas gets released straight into the room and if the flask is too hot, mass may be lost by evaporation

141

How can the rate of reaction be measured by the volume of gas given off?

This involves a gas syringe
The more gas given off in a certain time interval, the faster the reaction
Mostly accurate results
If the reaction is too vigorous, the plunger may blow out of the syringe

142

What is the collision theory?

The theory that the rate of reaction depends on how often and how hard particles collide with each other

143

How does temperature increase collisions?

As temperature increases gain more kinetic energy
Therefore they move faster
Causing more successful collisions

144

How does concentration/pressure increase collisions?

A higher concentration/pressure means more particles are squashed together
Therefore they are more likely to collide as there is less free space
So there are more frequent collisions

145

How does surface area increase collisions?

A larger surface area means there is more area for the particles to react with
So there is more frequent collisions

146

How does a catalyst increase collisions?

A catalyst provides a surface for reacting particles to stick to
Which increases the number of successful collisions

147

What is a catalyst?

A substance that speeds up a reaction without being changed or used up

148

What is the activation energy?

The minimum amount of energy required for particles to react

149

Advantages of catalysts

Used in many industrial reactions
Saves money
Allows reactions to work at lower temperatures saving energy
Can be reused

150

Disadvantages of catalysts

Expensive to buy and clean
Different catalysts are required for different reactions
Can stop working by impurities

151

What is an exothermic reaction?

When (heat) energy is transferred to the surrounding and is shown by a rise in temperature

152

Examples of exothermic reactions (3)

- burning fuels e.g combustion
- neutralisation reactions
- oxidation reactions
- everyday uses e.g hand warmers

153

What is an endothermic reaction?

Takes in (heat) energy from surroundings and is shown by a fall in temperature

154

Examples of endothermic reactions (2)

- thermal decomposition
- everyday uses e.g injury ice packs

155

Define anyhydrous

Without water

156

Define hydrated

With water

157

In reversible reactions why are they endothermic in one direction and exothermic in the other?

The energy absorbed by the endothermic reaction is equal to the energy released

158

What is the pH scale?

A measure of how acidic or alkaline a solution is

159

What would the pH of the strongest acid be?

0

160

What would the pH of the strongest alkaline be?

14

161

What does a pH of 7 suggest?

It is neutral, e.g pure water

162

How can you estimate the pH of a solution?

Using an indicator

163

How does universal indicator work?

It changes colour depending on whether it is above or below a particular pH

164

(s)

Solid

165

(l)

Liquid

166

(g)

Gas

167

(aq)

Dissolved in water

168

What is an acid?

An acid is a substance with a pH of less than 7

169

What ions do acids form in water?

They form H+ ions which make solutions acidic

170

What is an Alkali?

An alkali is a base that dissolves in water

171

What is a base?

A substance with a pH of above 7

172

What ions do alkalis form in water?

They form OH- ions that make solutions alkali

173

What is the reactions between acid and bases called?

A neutralisation reaction

174

What is the equation for a neutralisation reaction?

acid + base -> salt + water

175

What is the equation for a neutralisation reaction in terms of ions?

H+ (aq) + OH- (aq) -> H20 (l)

176

If a substance is neutral what colour will the indicator turn?

Green

177

What is the equation for the reaction of an acid and metal?

Acid + metal -> salt + hydrogen

178

How does the reactivity of a metal affect the rate of the reaction?

The more reactive the metal, the faster the reaction will be

179

Why does copper not react with dilute acids?

It is less reactive than hydrogen

180

In reactions of metal and acid, how can the speed be measured?

The rate at which bubbles of hydrogen are given off

181

What is the burning splint test?

The test for hydrogen which can be identified by placing a burning splint into the solution and hearing a squeaky pop

182

What does the name of the salt produced depend on?

The metal and acid used

183

Hydrochloric acid will produce which salts?

Chloride
E.g. magnesium chloride

184

Sulfuric acid will always produce which salts?

Sulfates
E.g Zinc sulfate

185

What is the reaction of an acid and metal oxide?

Acid + metal oxide -> salt + water (neutralisation reaction)

186

What is the reaction of an acid and metal hydroxide?

Acid + metal hydroxide -> salt and water (neutralisation reaction)

187

When ammonia dissolves in water what is the product?

An Alkaline solution

188

Reaction of ammonia and nitric acid equation

Ammonia + nitric acid -> ammonium nitrate

NH3 (aq) + HNO3 (aq) -> NH4NO3 (aq)

189

Why is the reaction of ammonia and nitric acid different to other neutralisation reactions?

There is NO water produced, only three ammonium salt

190

Why is ammonium nitrate a good fertiliser?

It has nitrogen from the ammonia and the nitric acid which plants require to make proteins

191

Which salts are soluble in water?

Most chlorides, sulfates and nitrates


(Except lead chloride, lead sulfate and silver chloride)

192

Which salts are insoluble in water?

Most oxides and hydroxides

193

How to make SOLUBLE salts with a metal/insoluble base

1. Pick the correct acid and base/insoluble salt
2. Add the metal, metal oxide or hydroxide to the acid which should then dissolve as it reacts.
3. The acid has been neutralised when excess solid sinks to the bottom
4. Filter out the excess solid parts to leave the salt solution
5. For pure crystals, evaporate some of the water to make it more concentrated and leave to evaporate (crystallisation)

194

How to make SOLUBLE salts using an alkali

Acid + alkali -> salt + water
1. Use universal indicator to mix and see when the reaction is finished and measure the amount you have used
2. Repeat without the indicator so the salt is not contaminated with indicator
3. Evaporate and crystallise

195

How to make INSOLUBLE salts using a precipitation reaction

Pick two solutions that contain the ions you need
Mix them together
Once the salt is precipitated, it will sink to the bottom
Filter the solution, wash and then dry it on filter paper

196

What are precipitation reactions used for?(2)

-To remove poisonous ions e.g lead from drinking water
-To treat effluent (sewage) and removed unwanted ions

197

What is electrolysis?

Passing an electric current through an ionic substance (that's molten or in solution) to break it down into the elements it's made up of

198

What is the electrolyte?

The liquid required to conduct the electricity

199

Why does electrolysis only occur in molten or dissolved ionic substances?

As electrolytes contain free ions that allow electricity to be conducted

200

Where do electrons move to during electrolysis?

Electrons are taken away from ions at the positive electrode and move the to the negative electrode

201

What do ions become when the lose or gain electrons?

Atoms or molecules

202

OIL RIG

Oxidation is losing electrons
(and gaining oxygen)
Reduction is gaining electrons
(and losing oxygen)

203

Electrolysis of molten lead bromide

-Lead is produces at the negative electrode (Reduction)
-Bromine is produced at the positive electrode (Oxidation)
-At the negative electrode, one lead ion accepts 2 electrons and becomes one lead atom
-At the positive electrode, two bromide ions lose one electron each to become one bromine molecule

204

What can affect the products formed by electrolysis?

The reactivity series of metals

205

How does the reactivity of metals affect products at the negative electrode?

Hydrogen js produced unless the metal is less reactive than hydrogen
This is because more reactive ions want to stay within the solution

206

How does the reactivity of metals affect products at the positive electrode?

If OH- and halide ions (Cl-, Br, l-) are present then one of the halide ions will form.
If no halide is present, oxygen will be formed

207

What are the products when sodium chloride solution is electrolysed? (3)

Hydrogen
Chlorine
Sodium hydroxide

208

Electrolysis of sodium chloride solution

-At the negative electrode, two hydrogen ions accept 2 electrons to become one hydrogen molecule
-At the positive ions, two chloride ions lose their electrons to become one chlorine molecule
-Sodium ions remain in solution as they are more reactive than hydrogen, and hydroxide ions from the water are left behind. Therefore sodium hydroxide is left in the solution.

209

Half equations for electrolysis of molten lead bromide

Negative electrode: Pb2+ + 2e- ---> Pb

Positive electrode: 2Br- ---> Br2 + 2e-

210

Half equations for electrolysis or sodium chloride solution

Negative electrode: 2H+ + 2e- ---> H2

Positive electrode:
2Cl- ---> Cl2 + 2e-
OR
2Cl- - 2e- ---> Cl2

211

Products from the electrolysis of sodium chloride solution

-Chlorine can be used in the production of bleach and plastics
-Sodium hydroxide is a strong alkali and is therefore used to make soap

212

Why is electrolysis used with aluminium?

It is used to remove aluminium (found naturally in compounds) from its ore which is bauxite

After mining and purifying, pure aluminium oxide is left (a white powder), so the aluminium gets extracted through electrolysis

213

Why is cryolite used in the electrolysis of aluminium

Aluminium oxide has a high MP (over 2000 degrees) so melting would be expensive
Instead dissolving it in molten cryolite would bring the temperate down to 900 degrees
This makes it cheaper and easier

214

Why are electrodes in the electrolysis of aluminium made of carbon?

It is a good conductor of electricity

215

Electrolysis of aluminium

Aluminium forms at the negative electrode
Oxygen forms at the positive electrode
At the positive electrode, carbon dioxide can get formed because the oxygen reacts with the carbon, therefore the positive electrodes have to get replaced as they can get eroded

216

Half equations for the electrolysis of aluminium

Negative electrode:
Al3+ + 3e- ---> Al

Positive electrode:
202- ---> O2 + 4e-

217

What is electroplating?

Electroplating used electrolysis to coat the surface of one metal with another

218

Uses of electroplating

Decoration - silver is attractive but expensive so it's character to plate a brass cup with silver instead
Conduction - metals like copper conduct electricity well so they're used to plays metals for circuits and computers

219

In electroplating what is at each electrode, and what is the electrolyte?

The negative electrode is the metal object you want to plate
The positive electrode is the pure metal you want it to be plated with
The electrolyte must contain a solution containing the ions of the plating metal

220

Electroplating of silver onto brass

Brass would be the negative electrode
A lump of pure silver would be the positive electrode
The electrolyte would be silver nitrate (as it includes silver ions)

221

Rate of reaction experiments (4)

HCL acid and marble chips
Magnesium and dilute HCL
Sodium Thiosulfate and HCL
Hydrogen peroxide

222

Explain the reaction of sodium thiosulfate and HCL

Both clear solutions
React to form a yellow precipitate (sulfur)
Time how long it takes for a black mark to no longer be seen as the sulfur turns cloudy
Repeat for different temps/concentrations
Use hot water bath so acid is not directly heated

223

Explain the decomposition of hydrogen peroxide

Shows the effect of different catalysts
The decomposition is usually quite slow
Manganese oxide catalyst speeds it up
( Or catalysts in potato peel/blood )
Oxygen is given off and if used to measure the rate of reaction using a gas syringe
2H202 (aq) ---> 2H20 (l) + O2 (g)