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Chemistry Paper 1 - C1, C2, C3, C4, C5, C6 > C4 - Chemical Changes > Flashcards

C4 - Chemical Changes Flashcards

Acids and bases, titrations, strong and weak acids, reactions of acids, reactivity series, separating metals from metal oxides, redox reactions, electrolysis, electrolysis of aqueous solutions.

1
Q

Acids and Bases -
What is the pH scale?

A

A measure of how acidic or alkaline a solution is.

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2
Q

Acids and Bases -
What does lower pH mean?

A

More acidic

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3
Q

Acids and Bases -
What does a higher pH mean?

A

More alkaline

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4
Q

Acids and Bases -
What is the pH of a neutral substance?

A

7

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5
Q

Acids and Bases -
Examples of items with pH of 1 to 13.5

A

pH 1 = car battery acid, stomach acid
pH 3 = vinegar, lemon juice
pH 4 = acid rain
pH 5 = normal rain
pH 7 = pure water
pH 8.5 = washing up liquid
pH 10 = pancreatic juice
pH 11 = soap powder
pH 12 = bleach
pH 13.5 = caustic soda (drain cleaner)

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6
Q

Acids and Bases -
What is an indicator?

A

A dye that changes colour depending on if it’s above or below a certain pH.

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7
Q

Acids and Bases -
What do some indicators contain?

A

Mixture of dyes mean they gradually change colour over broad range of pH - wide range indicators

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8
Q

Acids and Bases -
What are wide range indicators useful for?

A

estimating the pH of solution eg universal indicator gives colours on pH line

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9
Q

Acids and Bases -
What is a pH probe attached to a pH meter used to measure?

A

pH electronically

  1. probe placed in solution, pH given on a digital display as numerical value
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10
Q

Acids and Bases -
Why are pH probes and pH meter used instead of an indicator?

A

More accurate

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11
Q

Acids and Bases -
What do acids and bases do to each other?

A

Neutralise each other

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12
Q

Acids and Bases -
What is an acid?

A

Substance that forms aqueous solutions with a pH of less than 7

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12
Q

Acids and Bases -
What do acids form in water?

A

H+ ions

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13
Q

Acids and Bases -
What is a base?

A

Substance with a pH greater than 7

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14
Q

Acids and Bases -
What is an alkali?

A

A base that dissolves in water to form a solution with a pH greater than 7

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15
Q

Acids and Bases -
What do alkalis form in water?

A

OH- ions

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16
Q

Acids and Bases -
What is a reaction between acids and bases called and chemical reaction?

A

Neutralisation

acid + base > salt + water

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17
Q

Acids and Bases -
How can a neutralisation between acids and alkalis be seen in terms of H+ ions and OH- ions?

A

H+ + OH- > H2O

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18
Q

Acids and Bases -
What happens to the product when an acid neutralises a base?

A

Products are neutral (an indicator can be used to show neutralisation is over)

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19
Q

Acids and Bases -
What can neutralisation of strong acids and alkalis be used to calculate?

A

concentration of an acid or alkali by titration

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20
Q

Titrations -
What are titrations?

A

A method of analysing concentration of solutions

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21
Q

Titrations -
What do titrations allow you to do?

A

Find out exactly how much acid is needed to neutralise a quantity of alkali (or vise versa)

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22
Q

Titrations -
What can you use the data from a titration to do?

A

Work out concentration of the acid or alkali

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23
Q

Titrations -
Method to find out concentration of some alkali:

A
  1. Use pipette + pipette filter add set volume of alkali to conical flask
  2. Add two/ three drops of indicator
  3. Use a funnel, fill burette with acid of known concentration (make sure do below eye level - don’t want to be looking up if acid spills)
  4. Record initial volume of acid in burette
  5. Using burette, add acid to alkali a bit at a time - regularly swirl conical flask. ( go slow when adding acid when end point (colour change) is about to be reached.
  6. Indicator changes colour when all alkali neutralised (phenolphthalein pink in alkaline solution, colourless in acidic)
  7. Record final volume acid inn burette, use it and initial reading to calculate volume of acid used to neutralise the alkali.

( you can also do titrations the other way around)

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24
Q

Titrations -
What is a burette used for during a titration?

A
  • measure different volumes
  • let you add solution drop by drop
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25
Q

Titrations -
How do you increase the accuracy of a titration?

A
  • spot any anomalous results
  • several consistent readings
  • repeat experiment
  • calculate a mean and ignore anomalous results
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26
Q

Titrations -
What should the first titration you do be and why?

A

Rough - get approximate idea of where solution changes colour

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27
Q

Titrations -
What are examples of single indicators for titrations?

A
  • Litmus - blue in alkalis, red in acids
  • Phenolphthalein - pink in alkalis, colourless in acids
  • Methyl orange - yellow in alkalis, red in acids
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28
Q

Titrations -
Why are single indicators used in titrations?

A

Because you want to see a sudden colour change at the end point

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29
Q

Strong Acids and Weak Acids -
What do acids do in aqueous solutions?

A

Ionise - produce H+ ions (proton)

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30
Q

Strong Acids and Weak Acids -
What do strong acids do in water?

A

Completely ionise (all acids particles dissociate to release H+ ions)

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31
Q

Strong Acids and Weak Acids -
What are examples of strong acids and weak acids ?

A

Strong acids:
- sulfuric acid
- hydrochloric acid
- nitric acid

Weak acids:
- ethanoic acid
- citric acid
- carbonic acid)

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32
Q

Strong Acids and Weak Acids -
What do weak acids do in a solution?

A

Don’t fully ionise (small portion of acids particles dissociate to release H+ ions)

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33
Q

Strong Acids and Weak Acids -
What is the ionisation of a weak acid an example of?

A

A reversible reaction (sets up an equilibrium between undissociated and dissociated acid)

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34
Q

Strong Acids and Weak Acids -
What does the reaction of acids involve?

A

H+ ions reacting with other substances

  • if concentration of H+ ions is higher , rate of reaction faster, so strong acids more reactive than weak acids of the concentration.
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35
Q

Strong Acids and Weak Acids -
What is the pH of an acid or an alkali a measure of?

A

concentration of H+ ions in the solutions

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36
Q

Strong Acids and Weak Acids -
For every decrease of 1 on the pH scale, the concentration of H+ ions increase by?

A

a factor of 10

(so an acid that has a pH of 4 has 10 times the concentration of H+ ions of an acid with a pH of 5)

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37
Q

Strong Acids and Weak Acids -
What is the general formula for concentration of H+ ions in an acid?

A

Factor H+ ion concentration changes by = 10 to the power of -x

(x is the difference in pH eg if pH falls from 7 to 4 the difference is -3 and the factor the H+ ion concentration has increased by is 10 to the power of –3 so 3)

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38
Q

Strong Acids and Weak Acids -
When is the pH of a strong acid always less than the pH of weaker acid?

A

If they have the same concentration

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39
Q

Strong Acids and Weak Acids -
What does the strength of an acid tell you?

A

What proportion of the acid molecules ionise in water.

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40
Q

Strong Acids and Weak Acids -
What does concentration measure?

A

How much acid there is in a certain volume of water (basically how watered down your acid is)

41
Q

Strong Acids and Weak Acids -
What will decrease and increase despite whether the acid is strong or weak?

A

pH will decrease with increasing acid concentration

42
Q

Strong Acids and Weak Acids -
What does concentration describe?

A

The total number of dissolved acid molecules - not the number of molecules that are ionised to produce hydrogen ions.

43
Q

Reactions of Acids -
What are two examples of bases?

A
  • Metal oxides
  • metal hydroxides

(are examples of soluble compounds that dissolve in water)

44
Q

Reactions of Acids -
Will bases that don’t dissolve in water take part in a neutralisation reaction?

45
Q

Reactions of Acids -
What do all metal oxides and metal hydroxides react with acids to form?

A

A salt + water

46
Q

Reactions of Acids -
What does the salt produced depend on?

A

The acid and the metal ion in the oxide or hydroxide

eg
hydrochloric acid + copper oxide > copper chloride + water

hydrochloric acid = acid
copper = metal ion in oxide
copper oxide = metal oxide
copper chloride = salt

47
Q

Reactions of Acids -
What are metal carbonates an example of?

48
Q

Reactions of Acids -
What do metal carbonates react with an acid to produce?

A

Salt + water + carbon dioxide

49
Q

Reactions of Acids - RP
What can you make soluble salts using?

A

An insoluble base

50
Q

Reactions of Acids - RP
What is the method to making a soluble salt using an insoluble base?

A
  1. Insoluble metal oxide/ hydroxide/ carbonate and an acid depending on what product you want to form
  2. Gently warm dilute acid using bunsen burner, then turn off
  3. Add insoluble base to acid a bit at a time, until base in excess - know when in excess as when all acid neutralised solid sink to bottom of flask
  4. filter out excess solid to get salt solution
  5. Gently heat solution using water bath to evaporate some of water (make more concentrated) + stop heating + leave to cool.
  6. Crystals of salt form + filtered out of solution + dried (called crystallisation)
51
Q

Reactivity Series -
What does the reactivity series do?

A

Lists metals in order of their reactivity towards other substances

52
Q

Reactivity Series -
How is the reactivity of a metal determined?

A

How easily they lose electrons to form positive ions

53
Q

Reactivity Series -
What does it mean if the metal is higher up the reactivity series?

A
  • The more easily they form positive ions
  • The more easily it reacts with water or acid
54
Q

Reactivity Series -
What is the order of the reactivity series?

A

Potassium - most reactive
Sodium
Lithium
Calcium
Magnesium
Carbon - non metal but often included
Zinc
Iron
Hydrogen - non metal but often included
Copper - least reactive

55
Q

Reactivity Series -
What do an acid and a metal form when they are reacted together?

A

Salt + hydrogen

56
Q

Reactivity Series -
What does how a metal reacts with acids tell you about?

A

Their reactivity

57
Q

Reactivity Series -
How is the speed of a reaction between an acid and a metal indicated?

A

Rate at which the bubbles of hydrogen are given off

(less reactive metal on the reactivity series the less hydrogen given off)

58
Q

Reactivity Series -
What other method can you use to investigate the reactivity of metals?

A

Measuring the temperature change of the reaction with an acid or water over a set time period.

(if use same mass + surface area of metal, more reactive the metal means greater temperature change)

59
Q

Reactivity Series -
What is another method you can use to show the reactivity of metals?

A

reacting a metal with water to produce a metal hydroxide and hydrogen.

(potassium, sodium, lithium and calcium will all react with water but less reactive zinc, iron and copper won’t)

60
Q

Separating metals from metal oxides -
What do most metals have to be extracted from?

A

A compound (meaning more work is required)

61
Q

Separating metals from metal oxides -
What do metals often have to be separated from?

A

Their oxides (ores that metals need to be extracted from)

61
Q

Separating metals from metal oxides -
What is a reaction that separates a metal from its oxide called?

A

Reduction reaction

61
Q

Separating metals from metal oxides -
How is metal ore formed?

A

Metal is oxidised through gaining oxygen in oxidation to form metal oxide
eg magnesium is oxidised to make magnesium oxide

62
Q

Separating metals from metal oxides -
How is metal extracted?

A

The metal oxide is reduced as it loses oxygen through reduction to form metal
eg copper oxide is reduced to copper

63
Q

Separating metals from metal oxides -
How can some metals be extracted from their ores chemically?

A

By reduction using carbon

64
Q

Separating metals from metal oxides -
What happens during a reduction to extract metal using carbon?

A

Ore reduced (oxygen removed from it) + carbon gains oxygen so is oxidised.

65
Q

Separating metals from metal oxides -
What determines whether a metal can be extracted by reduction with carbon?

A

Position of metal in the reactivity series
- metals higher than carbon have to be extracted using electrolysis - expensive
- metals below carbon extracted using reduction using carbon - carbon only take the oxygen away from less reactive than itself

potassium, sodium, lithium, calcium, magnesium - electrolysis

zinc, iron, copper - reduction using carbon

66
Q

Redox reactions -
What does OILRIG stand for?

A

Oxidation
Is
Loss
Reduction
Is
Gain

66
Q

Redox reactions -
What is a redox reaction?

A

When electrons are transferred

67
Q

Redox reactions -
What is oxidation and reduction in terms of in redox reactions?

A

Electrons

(not oxidation as in addition of oxygen or reduction as the removal of oxygen)

68
Q

Redox reactions -
What is a loss of electrons called?

69
Q

Redox reactions -
What is a gain of electrons?

69
Q

Redox reactions -
When do oxidation and reduction happen?

A

At the same time

70
Q

Redox reactions -
What are all the reactions of metals and acids an example of?

A

Redox reactions

71
Q

Redox reactions -
What is another example of a redox reaction?

A

Displacement reactions

72
Q

Redox reactions -
What do displacement reactions involve?

A

A more reactive metal displacing a less reactive metal from its compound

73
Q

Redox reactions -
What happens to the metal ion and metal atom in a displacement reaction?

A

Metal ion - always gains electrons so reduced eg copper gains 2 electrons to become copper atom = Cu 2+ + 2e - > Cu

Metal atom - always loses electrons so oxidised eg iron loses 2 electrons to become 2+ ion = Fe > Fe2+ + 2e -

74
Q

Redox reactions -
What are shown in an ionic equation?

A

Only the particles that react and the products they form

75
Q

Redox reactions -
What are the ions that don’t change in the reaction called?

A

Spectator ions

76
Q

Redox reactions -
What do ionic equations concentrate on?

A

Substances which are oxidised or reduced

77
Q

Electrolysis -
What does electrolysis mean?

A

Splitting up with electricity

78
Q

Electrolysis -
What happens during electrolysis?

A
  1. An electric current is passed through an electrolyte. The ions move towards the electrodes where they react and the compound decomposes.
  2. Positive ions in electrolyte move towards cathode (negative electrode) and gain electrons (reduced)
  3. Negative ions in electrolyte move towards anode (positive electrode) and lose electrons (oxidised)
  4. Creates a flow of charge through electrolyte as ions travels to electrodes.
  5. As ions gain and lose electrons, form uncharged elements and are discharged from the electrolyte.
79
Q

Electrolysis -
What is an electrolyte?

A

A molten or dissolved ionic compound - a liquid or solution that can conduct electricity.

80
Q

Electrolysis -
What does the electrolysis of molten ionic solids form?

81
Q

Electrolysis -
What is an electrode?

A

A solid that conducts electricity and is submerged in the electrolyte.

82
Q

Electrolysis -
Why can’t an ionic solid be electrolysed?

A

The ions are in fixed positions and can’t move

83
Q

Electrolysis -
Why can molten ionic compounds be electrolysed?

A

Ions move freely and conduct electricity

84
Q

Electrolysis -
What are molten ionic liquids such as lead bromide always broken up into during electrolysis?

A

Their elements

85
Q

Electrolysis -
When are metal extracted from their ores using electrolysis?

A
  • metal is too reactive to be reduced with carbon
  • metal reacts with carbon
86
Q

Electrolysis -
What is a problem of extracting metals from their ores using electrolysis?

A
  • expensive: lots of energy required to melt the ore and produce the required current
87
Q

Electrolysis -
What is an example of a metal being extracted from its ore using electrolysis and method?

A
  1. Aluminium extracted from ore bauxite by electrolysis. Bauxite contains aluminium oxide.
  2. Aluminium oxide very high melting point - mixed with cryolite to lower
  3. Molten mixture contains free ions - conduct electricity
  4. Positive aluminium ions attracted negative electrode where each pick up 3 electrons and turn to neutral aluminium atom - sink to bottom of tank
  5. Negative oxygen ions attracted positive electrode - each lose two electrons - neutral oxygen atom combine to form O2 molecules
88
Q

Electrolysis -
Why does the anode need to be replaced regularly?

A

Made of carbon so reacts with oxygen to produce CO2

89
Q

Electrolysis of aqueous solutions -
What is in the aqueous solution?

A
  • ions from ionic compounds
  • hydrogen ions (H+) - from water
90
Q

Electrolysis of aqueous solutions -
What is present at the cathode?

A

H+ ions and metal ions

91
Q

Electrolysis of aqueous solutions -
When will hydrogen be formed at the cathode?

A

If metal ions form an elemental metal more reactive than hydrogen

92
Q

Electrolysis of aqueous solutions -
What is produced if the metal ions form an elemental metal less reactive than hydrogen?

A

Solid layer of pure metal

93
Q

Electrolysis of aqueous solutions -
What will be present at the anode if molecules of chlorine, bromine and iodine are formed?

A
  • OH - ions
  • Halide ions (Cl-, Br-, I-)
94
Q

Electrolysis of aqueous solutions -
What is formed and discharged at the anode if no halide ions are present?

A
  • OH- ions discharged
  • Oxygen formed
95
Q

Electrolysis of aqueous solutions - RP
What are the tests after electrolysis of aqueous solutions for gaseous products?

A
  • Chlorine: bleaches damp litmus paper (white)
  • Hydrogen: squeaky pop with a lighted splint
  • Oxygen: relight a glowing splint
96
Q

Electrolysis of aqueous solutions -
What do half equations show?

A

The reactions at the electrodes

97
Q

Electrolysis of aqueous solutions -
Where to look for examples of electrolysis of aqueous solutions?

A

Chemistry textbook page 59

(wasn’t able to type it out so it was understandable)

Chemistry Paper 1 - C1, C2, C3, C4, C5, C6 (5 decks)

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