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Science - C6 > C6 > Flashcards

C6 Flashcards

0
Q

What happens to a reaction if reduction takes place?

A

reduction is the gain of electrons

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1
Q

What happens in a reaction if something is oxidised?

A

Oxidation is the loss of electrons

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2
Q

What does redox mean?

A

It means that whenever reduction occurs so must oxidation.

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3
Q

What is the substance that causes something to be oxidised called?

A

An oxidising agent.

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4
Q

Whenever an oxidising agent occurs what happens to it?

A

It is reduced - redox

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5
Q

What is electrolysis?

A

It is the breaking up of a substance using electricity.

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6
Q

What is the substance in electrolysis called and what does it have to be made of?

A

Electrolyte, has to be liquid or liquid dissolved in water

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7
Q

Why can a solid not be an electrolyte?

A

Because the ions must be free moving, which is the case in liquids, but in solids the ions are in fixed positions and can not move.

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8
Q

In electrolysis where is the electricity supplied through?

A

The electrodes

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9
Q

Give an example of an electrode?

A

Carbon rods

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10
Q

In electrolysis what is the positive terminal called?

A

Anode

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11
Q

In electrolysis what is the negative terminal called? I

A

Cathode

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12
Q

What current must the electricity have?

A

DC direct current

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13
Q

In electrolysis which ions move to which electrode? And why?

A

Positive ions = cathode
Negative ions = anode
Because ions move to the oppositely charged electrode.

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14
Q

What happens to the negative ions at the anode?

A

The ions loose extra electrons to become neutral.

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15
Q

In electrolysis what happens to the positive ions at the cathode?

A

The ions gain enough electrons to neutralise their positive charge so that they become neutral.

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16
Q

What is different about the electrolysis of aqueous solutions?

A

Ions from the water are also present eg. Hydrogen and hydroxide ions

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17
Q

In the electrolysis of aqueous solutions what is the rule for what happens at the anode?

A

If a halogen is available it will be formed, but if not the. The hydroxide ion breaks down to release oxygen.

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18
Q

In the electrolysis of aqueous solutions what is the rule for which ion goes to the cathode?

A

The reactivity series tells you, the least reactive substance is discharged and ions that aren’t discharged remain in the solution.

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19
Q

Does the solution in electrolysis have to be molten?

A

No, it can be aqueous

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20
Q

Describe the electrolysis of copper chloride.

A

An electrical current is sent through the electrolyte which causes it to decompose. This starts a flow of charge through the electrolyte. The negative chloride ions attract to the anode and form chlorine gas, the positive copper ions attract to the cathode to form pure copper.

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21
Q

What are the half equations for the electrolysis of CuSO4?

A

Anode: _ _
4OH === O2 + 2H2O + 4e
cathode: 2+ _
Cu + 2e ==== Cu

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22
Q

At which electrode in electrolysis is the metal always formed?

A

Cathode - except for Hydrogen

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23
Q

What is the oxidation number of any pure element?

A

0

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24
Q

What is the oxidation number of hydrogen when it is in a compound without a metal?

A

+1, with a metal -1

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25
Q

What is the oxidation number of O in a compound? Or with H2 or Na2

A

-2, -1

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26
Q

What is the oxidation number of alkali metals in compounds?

A

+1

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27
Q

What is a fuel cell?

A

An electrical cell that is supplied with a fuel and oxygen, and uses energy from the reaction to produce electricity.

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28
Q

Give an example of a fuel cell?

A

Hydrogen-oxygen fuel cell.

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29
Q

What type of reaction takes place in a fuel cell and why?

A

Exothermic, because it takes in energy to break bonds and gives out energy to make new bonds.

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30
Q

What does a hydrogen fuel cell produce?

A

It uses hydrogen and oxygen to produce water.

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31
Q

Describe how a hydrogen-oxygen fuel cell works in terms of a redox reaction?

A

The H2 attracts to the anode and the O2 attracts to the cathode. At the cathode O2 gains electrons and reacts with water to make OH- ions. This is reduction. The OH- ions in the electrolyte move to the anode and combine with the hydroxide ions to produce H2O + electrons. This oxidation. Electrons then flow through a circuit from anode to cathode which creates an electrical current.

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32
Q

What is the half equation for a hydrogen-oxygen fuel cell at the cathode?

A

O2 + 4e- + 2H2O ==== 4OH-

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33
Q

What is the half equation for the hydrogen-oxygen fuel cell at the anode?

A

2H2 + 4OH- ===== 4H2O + 4e-

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34
Q

Give 3 advantages of using fuel cells.

A

More efficient then power stations.
No pollution, only product is water.
Electricity is generated directly from reaction.

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35
Q

Give 2 disadvantages to the use of fuel cells.

A

Producing H2 uses a lot of energy which could cause pollution.
Often contain poisonous catalysts which will eventually have to be disposed of, time money and environmental issues.

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36
Q

Why are hydrogen-oxygen fuel cells used in spacecrafts?

A

Lightweight and compact, won’t use up valuable room.
No moving parts which might go wrong
Some product can be used as drinking water.
No waste product to get rid of.

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37
Q

Why is the car industry interested in fuel cells?

A

Don’t produce conventional pollutants.
Hydrogen can be obtained by decomposing water which is largely available meaning we won’t have to use non-renewable fuels.

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38
Q

What will cause iron to rust?

A

Both oxygen and water

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39
Q

What is the word equation for the rusting of iron?

A

Iron + water + oxygen ===== hydrated iron(III)oxide

40
Q

Why is the rusting if iron a redox equation?

A

Iron looses 3 electrons when it reacts with water. This is oxidation. Oxygen gains 2 electrons when it reacts with iron. This is reduction.

41
Q

Name a way that can stop iron from rusting.

A

By coating the iron with a barrier eg. Paint. Which will keep the water and oxygen out and prevent it from rusting. Oiling/greasing can be used for moving parts.

42
Q

What is tin playing?

A

Tin plating is where a coat of tin is applied to an object to act as a barrier, stopping water and oxygen from reacting with the surface of iron.

43
Q

What is a disadvantage of tin plating?

A

If the tin is scratched to reveal iron, the iron will loose electrons and rust even faster.

44
Q

What is galvanising?

A

Galvanising is where a coat of zinc is put into an object and acts as a sacrificial protection.

45
Q

Why does galvanising iron prevent it from rusting?

A

It’s more reactive than iron so it will loose electrons in preference to iron. It also acts as a barrier blocking out water and oxygen.

46
Q

What do CFCs stand for?

A

Chlorofluorocarbons

47
Q

What first impression did scientists have about CFCs?

A

Initially enthusiastic because of their useful properties.

48
Q

What are CFCs useful properties?

A

Chemically inert - they won’t react with other substances
Non-flammable
Low boiling point
Insoluble in water

49
Q

By 1970 how did scientists view CFCs now?

A

They had gathered evidence that CFCs were responsible for ozone depletion.

50
Q

What does the ozone layer do?

A

Absorbs and traps UV emitted from the sun preventing most from reaching the earths surface.

51
Q

How do CFCs interfere with the ozone layer?

A

They interfere with the process of the ozone being broken down and reformed by UV. They cause molecules to break down at a faster rate than they can be reformed.

52
Q

Why is having a hole in the ozone layer bad?

A

More UV light could reach the earths surface causing an increase in sunburn, ageing of skin, skin cancers and cataracts.

53
Q

What have been used to replace CFCs? And why?

A

Alkanes - hydrocarbons
HFCs
Because they don’t damage the ozone layer

54
Q

What in CFCs damages the ozone? And why?

A

Freon - 12
When it enters the atmosphere UV causes freon - 12 bonds to break leaving a chlorine with an unpaired electron - a radical. These radicals female the ozone layer.

55
Q

Show the freon - 12 reacting with UV in terms of equations.

A

CF2Cl2 ==== Cl• + CF2Cl•
Cl• + O3 === ClO• + O•
ClO• + O• === Cl• + O2

56
Q

What are chlorine radicals? What does this mean?

A

Regenerated, 1 chlorine radical can destroy many ozone molecules.

57
Q

Why do scientists now realise that CFCs being inert is a bad thing?

A

Because it means they stay in the atmosphere for a very long time and will do a lot of damage.

58
Q

What is hard water?

A

Water which contains high concentrations of magnesium ions and calcium ions.

59
Q

Where is hard water formed?

A

Formed in areas where natural water flows over rocks which contain calcium and magnesium compounds.

60
Q

What do the rocks that hard water contain which cause hard water? And why does it cause hard water?

A

Calcium carbonate, which is insoluble, reacts with CO2 and H2O and forms soluble calcium hydrogen carbonate, which is then carried through water and later collected in resviours.

61
Q

What is a disadvantage to hard water?

A

It makes soap ineffective, doesn’t allow soap to form a larger easily which is needed to wash away grease and dirt in the water.

62
Q

How does hard water interfere with soap?

A

Mg2+ and Ca2+ interfere with this process by reacting with soap to form a deposit of scum. This is a precipitation reaction.

63
Q

How can you get soap to Lather in hard water?

A

Add more soap - which will cost more

64
Q

How can you test how hard water is?

A

You can see how soap you need before it begins to lather. The more soap you need the harder the water.

65
Q

What is temp hardness caused by?

A

Caused by calcium carbonate ions in calcium hydrogen carbonate.

66
Q

What is permanent hardness caused by?

A

Caused by dissolved calcium sulphate.

67
Q

How can only temp hardness be removed?

A

By boiling it - calcium hydrogen carbonate decomposes to form insoluble CaCO3.

68
Q

How can both types of water hardness be removed?

A

By adding sodium carbonate - carbonate ions join into the Ca2+ ions to form an insoluble precipitate of CaCO3.

69
Q

What do all alcohols have in common?

A

They all have an oxygen atom bonded to a hydrogen atom.

70
Q

In alcohols, how-many bonds does each element have: Carbon, oxygen and hydrogen?

A 
Carbon = 4 bonds 
Hydrogen = 1 bond 
Oxygen = 2 bonds
71
Q

Name the 5 main types of alcohol and their formula in order.

A 
Methanol - CH3OH
Ethanol - C2H5OH
Propanol - C3H7OH
Butanol - C3H9OH
Pentanol - C4H11OH
72
Q

What is fermentation?

A

It is the process used to convert sugars like glucose into ethanol.

73
Q

How is fermentation brought about?

A

Through enzymes in the yeast which act as biological catalysts.

74
Q

Why does the temperature in fermentation have to be controlled?

A

Because if it’s too cold the enzymes will be inactive - slow reaction.
If it’s too hot the enzymes will denature.

75
Q

Why do you have to prevent oxygen getting to the alcohol in fermentation?

A

Oxygen converts ethanol into ethanoic acid.

76
Q

In fermentation how do you get pure ethanol?

A

By using fractional distillation after the reaction has stopped.

77
Q

What is the process of hydrating?

A

Hydrating is the industrial method for producing ethanol. It’s when Ethene reacts with steam to make ethanol.

78
Q

In the process of hydrating what is the optimum temp and pressure?

A 
Temp = 300 degrees 
Pressure = 70 atmospheres
79
Q

What is the catalyst in the method of hydrating?

A

Steam heated over a heated phosphoric acid.

80
Q

In terms of manufacture what is the hydrating and fermentation processes like?

A 
F = batch process which is slow and inefficient. 
H = continuous process which is quicker but more expensive.
81
Q

In terms of sustainability what is the hydrating and fermentation processes like?

A 
F = renewable fuel because it is made from renewable resources.  
H = non- renewable because it's made from crude oil which will eventually run out.
82
Q

In terms of purity what is the hydrating and fermentation processes like?

A 
F = has to be distilled before use - not very pure.
H = higher purity than fermentation
83
Q

In terms of atom economy what is the hydrating and fermentation processes like?

A 
F = lower than hydration as not all reactants are used to make ethanol. 
H = higher than fermentations
84
Q

Give 3 examples of animal fats and oils

A

Lard
Blubber
Cod liver oil

85
Q

Give 3 exams of vegetable fats and oils

A

Walnut oil
Coconut oil
Olive oil

86
Q

What are fats and oils and how are they produced?

A

They are esters which are produced when glycerol reacts with fatty acids.

87
Q

Why don’t oils mix in water?

A

They are immiscible.

88
Q

How can you mix water and oil to make an emulsion.

A

To make an emulsion you shake the two vigorously together, breaking up the oil into small droplets which will disperse through the water.

89
Q

Give an example of an emulsion of oil in water.

A

Milk

90
Q

Give an example of an emulsion for water in oil.

A

Butter

91
Q

How do vegetable oils get made into soap?

A

Natural fats are boiled with sodium hydroxide which splits up the fats and oils into soap and glycerol. This is called saponification.

92
Q

What do oils and fats have long molecules of?

A

Carbon atoms

93
Q

What kind of covalent bonds do saturated and unsaturated oils and fats have between carbons?

A 
Saturated = a single covalent bond
Unsaturated = at least one double covalent bond.
94
Q

What is the name of the unsaturated fat that only has one double covalent bond between carbon?

A

A monounsaturated fat

95
Q

What is the name of the unsaturated fat that has more than one double covalent bond between carbon?

A

Polyunsaturated fats

96
Q

How can you test whether an oil or fat is unsaturated or saturated?

A

You add bromine or bromine water to it, it stays orange it’s saturated and if it goes courses it’s unsaturated.

97
Q

What can natural unsaturated oils do?

A

Reduce the amount of blood cholesterol.

Science - C6 (1 decks)

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