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GCSE Chemistry > Topic 3: Chemical Changes > Flashcards

Topic 3: Chemical Changes Flashcards

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1
Q

What is the pH scale?

A

pH 0-6 = acids
pH 7 = neutral
pH 8-14 = alkalis

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2
Q

What happens to acidity as you decrease pH?

A

As you go down the pH scale, acidity increase

SO

pH 0 = most acidic
pH 14 = most alkali

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3
Q

What do acids form in water?

A

H+ ions

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4
Q

What do alkalis form in water?

A

OH- ions

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5
Q

What is the trend between H+ concentration and pH?

A

The higher H+ concentration, the lower the pH

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6
Q

What is the trend between OH- concentration and pH?

A

The higher the OH- concentration, the higher the pH

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7
Q

What are the three indicators we need to know?

A

Litmus
Methyl orange
Phenolphthalein

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8
Q

What colour is litmus when it’s in a solution that’s acidic?

A

Red

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9
Q

What colour is litmus when it’s in a solution that’s neutral?

A

Purple

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10
Q

What colour is litmus when it’s in a solution that’s alkaline?

A

Blue

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11
Q

What colour is methyl orange when it’s in a solution that’s acidic?

A

Red

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12
Q

What colour is methyl orange when it’s in a solution that’s neutral?

A

Yellow

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13
Q

What colour is methyl orange when it’s in a solution that’s alkaline?

A

Yellow

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14
Q

What colour is phenolphthalein when it’s in a solution that’s acidic?

A

Colourless

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15
Q

What colour is phenolphthalein when it’s in a solution that’s neutral?

A

Colourless

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16
Q

What colour is phenolphthalein when it’s in a solution that’s alkaline?

A

Pink

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17
Q

What is the general equation for a neutralisation reaction?

A

Acid + base —> salt + water

BASHO

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18
Q

What are properties of the products in a neutralisation reaction?

A

They’re neutral

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19
Q

What salt is produced if HCl is used as the acid in the reaction?

A

… chloride

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20
Q

What salt is produced if H2SO4 is used as the acid in the reaction?

A

… sulfate

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21
Q

What salt is produced if HNO3 is used as the acid in the reaction?

A

… nitrate

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22
Q

What are the 4 reactions of acids?

A

Acid + metal oxide —> salt + water
Acid + metal hydroxide —> salt + water
THESE ARE NEUTRALISATION REACTIONS (HAVE A BASE) - BASHO

Acid + metal carbonate —> salt + water + carbon dioxide
THIS IS A CASHOCO REACTION

acid + metal —> salt + hydrogen
THIS IS A MASH REACTION

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23
Q

What is the test for hydrogen?

A

Squeaky pop test:
1. Place a lit splint in a test tube
2. If it makes a squeaky pop sound then hydrogen is present

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24
Q

What is the test for carbon dioxide?

A

If limewater turns cloud when supplied with a gas, carbon dioxide is present

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25
Q

What is a strong acid?

A

An acid that completely ionises and dissociates in water to produce hydrogen ions

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26
Q

Examples of strong acids?

A

Hydrochloric acid
Sulfuric acid
Nitric acid

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27
Q

What is a weak acid?

A

An acid that partially ionises and dissociates in water to produce hydrogen ions

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28
Q

Examples of weak acids?

A

Ethanoic acid
Citric acid
Carbonic acid

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29
Q

What is acid strength a measure of?

A

The proportion of acid molecules that ionise in water

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30
Q

What is acid concentration a measure of?

A

The number of acid molecules in a certain volume of water

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31
Q

What concentration do dilute acids have?

A

Dilute acids have a low concentration

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32
Q

What concentration do concentrated acids have?

A

Concentrated acids have a high concentration of

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33
Q

What happens to pH as acid concentration increases in both types of acids?

A

pH decreases as acid concentration increases

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34
Q

What is pH?

A

A measure of the concentration of H+ ions in a solution

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35
Q

What happens to the pH of a solution if its H+ concentration increases by 10?

A

It decreases by 1

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36
Q

What happens to the pH of a solution if its H+ concentration decreases by 10?

A

It increases by 1

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37
Q

What pH on the pH scale has the highest H+ ion concentration?

A

pH 0 (lowest pH) (most acidic)

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38
Q

What pH on the pH scale has the lowest H+ ion concentration?

A

pH 14 (highest pH) (most alkaline)

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39
Q

What happens to pH of an acid if its strength increases?

A

pH decreases

40
Q

Show the pH scale in terms of H+ ion concentration

A

pH 0 (-10 H+ ions) pH 1 (-10 H+ ions) pH 2 (-10 H+ ions) pH 3 (-10 H+ ions) pH4 etc.

41
Q

Are common salts of sodium, potassium and ammonium soluble?

A

Yes

42
Q

Are nitrates soluble?

A

Yes

43
Q

Are common chlorides soluble?

A

Yes EXCEPT SILVER CHLORIDE AND LEAD CHLORIDE

44
Q

Are common sulfates soluble?

A

Yes EXCEPT LEAD SULFATE, BARIUM SULFATE AND CALCIUM SULFATE

45
Q

Are common carbonates and hydroxides soluble?

A

No EXCEPT FOR SODIUM, POTASSIUM AND AMMONIUM ONES

46
Q

What does soluble mean?

A

A substance that can be dissolved in a liquid

47
Q

What does insoluble mean?

A

A substance that doesn’t dissolve in a liquid

48
Q

How can insoluble salts be made using 2 soluble reactants?

A
  1. Soluble salts in a solution are added and mixed in a flask
  2. A precipitate is formed
  3. Use filter paper and a filter funnel to get rid of the solution and leave behind a dry precipitate (the insoluble salt)
  4. Rinse the precipitate with distilled water then leave it to dry in a warm oven
49
Q

What are the two ways that a soluble salt can be made?

A
  1. Using an acid and an insoluble base - filtration then crystallisation
  2. Using an acid and an alkali (soluble base) - titration then crystallisation
50
Q

How can a soluble salt be made using an acid and an insoluble base?

A
  1. An insoluble base is added to the acid
  2. The solid reactants are then removed using filter paper and a filter funnel to leave behind the products
  3. Repeat the process with excess insoluble base to make sure all of the acid reacts
  4. The salt and water that are produced are then heated gently to crystallise the salt
  5. The crystals are then filtered off and are left to dry
51
Q

How can a soluble salt be made using an acid and an alkali (soluble base)?

A
  1. Measure the acid using a pipette
  2. Slowly add the alkali using a titrator to the acid and indicator
  3. Stop adding the alkali when the indicator changes colour (so you know the volume needed)
  4. Repeat the process with the same volumes of acid and alkali but without the indicator to get a solution of salt and water
  5. The salt and water that are produced are then heated gently to crystallise the salt
  6. The crystals are then filtered off and are left to dry

THIS IS CALLED TITRATION

52
Q

What is electrolysis?

A

Passing an electric current through an electrolyte, causing it to decompose

53
Q

What is an electrolyte?

A

A molten or dissolved ionic compound

54
Q

What is a cathode?

A

Negative electrode

55
Q

What is an anode?

A

Positive electrode

56
Q

What power supply is used for electrolysis?

A

d.c. power supply

57
Q

What does the set up of electrolysis look like when the electrolyte is a dissolved ionic compound?

A

There’s a:
-cathode
-anode
-solution
-d.c. power supply

58
Q

What does the set up of electrolysis look like when the electrolyte is a molten ionic compound?

A

There’s a:
-cathode
-anode
-crucible
-the molten compound
-Bunsen burner
-d.c. power supply

59
Q

What should the electrodes be in electrolysis?

A

Inert - unreactive
E.g. graphite, platinum

60
Q

What electrode attracts cations?

A

Cathode (because it’s the negative anode and opposite charges attract)

61
Q

What anode attracts anions?

A

Anode (because it’s the positive anode and opposite charges attract)

62
Q

What occurs at the cathode (reduction or oxidation)?

A

Reduction

63
Q

What occurs at the anode (reduction or oxidation)?

A

Oxidation

64
Q

How to remember what happens (oxidation or reduction) at each electrode?

A

RedCat - Reduction at Cathode
AngryOx - Anode has Oxidation

65
Q

What is reduction?

A

Gain of electrons

66
Q

What is oxidation?

A

Loss of electrons

67
Q

How to remember what happens during oxidation and reduction?

A

OIL RIG - oxidation is loss & reduction is gain

68
Q

What is a half equation?

A

An equation that shows how electrons are transferred during reactions

69
Q

How are half equations formed? Use the example of hydrogen.

A
  1. Write the thing being oxidised or reduced as the reactant
  2. Write the thing that the reactant is oxidised or reduced to as the product
  3. If the element is being reduced write the electron on the reactants side, if it’s being oxidised write the electron symbol on the products side
  4. Balance the numbers of atoms including the electron

E.g. 2H+ + 2e- —> H2

70
Q

What is produced at the cathode in the electrolysis of molten ionic compounds?

A

Metal ions move towards the cathode and are reduced and produced DOESN’T MATTER IF ITS LESS REACTIVE THAN HYDROGEN

71
Q

What is never produced at the anode in electrolysis of aqueous solutions?

A

Sulfur gas - SO4

72
Q

What is produced at the anode in electrolysis of molten ionic compounds?

A

The gas in the compound as they’re oxidised

73
Q

What happens in the electrolysis of molten lead bromide?

A
  1. The electrolyte is lead bromide
  2. Bromine gas is given off at the anode - as negative non metal (Br-) ions move towards the anode and are oxidised (2Br- —> Br2 + 2e-)
  3. Lead metal ions move towards the cathode and are reduced (Pb2+ + 2e- —> Pb)
  4. Molten lead metal sinks to the bottom
74
Q

What is produced instead of sulfur gas at the anode in electrolysis of aqueous solutions? What does it come from?

A

Oxygen and water - comes from the OH- ions in the electrolyte

75
Q

What is produced at the anode in electrolysis of aqueous ionic compounds?

A

A halogen (gas) is produced if halide ions are present in the solution
BUT IF no halide ions are in the solution, O2 and H2O are produced e.g. sulphur

76
Q

What is produced at the cathode in electrolysis of aqueous ionic compounds?

A

A metal is produced at the cathode if it’s less reactive than hydrogen
BUT…
If hydrogen is more reactive than the metal in the compound, then hydrogen is produced

77
Q

What sinks to the bottom in electrolysis of molten ionic compounds?

A

The molten metal in the compound

78
Q

What is produced at the cathode and at the anode in the electrolysis of aqueous copper chloride? WITH HALF EQUATIONS

A

Cathode - copper (Cu2+ + 2e- —> Cu)

Anode - chlorine (2Cl- —> Cl2 + 2e-)

79
Q

What is produced at the cathode and at the anode in the electrolysis of aqueous sodium chloride? WITH HALF EQUATIONS

A

Cathode - hydrogen (2H+ + 2e- —> H2)

Anode - chlorine (2Cl- —> Cl2 + 2e-)

80
Q

What is produced at the cathode and at the anode in the electrolysis of aqueous sodium sulfate? WITH HALF EQUATIONS

A

Cathode - hydrogen (2H+ + 2e- —> H2)

Anode - oxygen and water (4OH- —> O2 + 2H2O + 2e-)

81
Q

What is produced at the cathode and at the anode in the electrolysis of aqueous water that’s acidified with sulfuric acid? WITH HALF EQUATIONS

A

Cathode - hydrogen (2H+ + 2e- —> H2)

Anode - oxygen and water (4OH- —> O2 + 2H2O + 2e-)

82
Q

What is the process of purifying copper?

A
  1. A pure copper cathode and an impure copper anode are used
  2. The electrolyte is CuSO4 solution (copper sulfate)
  3. The copper ions from the anode are attracted to the cathode - as they’ve got a charge of 2+
83
Q

What do the impurities of the impure copper anode do in the purifying of copper?

A

They form a sludge at the bottom

84
Q

What happens to the cathode during the purifying of copper?

A

It increases in mass and size - the copper ions in the anode and solution are attracted and move to it so it gains ions

85
Q

What happens to the anode during the purifying of copper?

A

It loses mass and size - the copper ions in it are attracted and move to the cathode and the impurities in it form a sludge

86
Q

What is the half equation at the anode during the purifying of copper?

A

Cu —> Cu2+ + 2e-

87
Q

What is the half equation at the cathode during the purifying of copper?

A

Cu2+ + 2e- —> Cu

88
Q

How is copper extracted from its ore? What are the properties of this copper?

A

Reduction with carbon - results in impure copper WHICH IS PURIFIED USING ELECTROLYSIS

89
Q

NEUTRALISATION CORE PRACTICAL: What is the process used to investigate neutralisation?

A
  1. Add a set mass of calcium oxide to a set volume of hydrochloric acid
  2. Record pH of solution after reaction finishes using pH probe or universal indicator paper
  3. Keep adding set mass of calcium oxide and measuring pH until some calcium oxide remains at the bottom - this means all acid has reacted
  4. Plot a graph to show how pH changes with mass of base added
90
Q

COPPER SULFATE CORE PRACTICAL: What is the process of creating copper sulfate?

A
  1. Add excess copper oxide to dilute sulfuric acid warmed using a water bath
  2. Mix using a stirring rod
  3. Filter the solution using a filter paper in funnel - filtration
  4. Slowly evaporate some of the copper sulfate using a Bunsen burner then leave it to cool and crystallise
  5. Filter the soluble salt off and leave it to dry
91
Q

ELECTROLYSIS OF COPPER SULFATE CORE PRACTICAL: What is the process of the electrolysis of copper sulfate using inert graphite electrodes?

A
  1. Have a dc power supply to an anode and a cathode inside the copper sulfate solution
  2. The copper metal will be produced at the cathode (it’s less reactive than hydrogen)
  3. Oxygen gas and water are produced at anode (produces bubbles as oxygen forms)
92
Q

ELECTROLYSIS OF COPPER SULFATE CORE PRACTICAL: What is the process of the electrolysis of copper sulfate using copper electrodes?

A
  1. Have a power supply to a copper anode and a copper cathode
  2. During reaction, mass of anode decreases and mass of cathode increases
  3. Dry and weigh the electrodes before and after the reaction to find a change in mass
93
Q

ELECTROLYSIS OF COPPER SULFATE CORE PRACTICAL: What is the independent and dependent variable the electrolysis of copper sulfate using copper electrodes?

A

Independent: current supplied
Dependent: change in mass of electrodes

94
Q

ELECTROLYSIS OF COPPER SULFATE CORE PRACTICAL: Why does mass of cathode increase and mass of anode decrease in the electrolysis of copper sulfate using copper electrodes?

A

Cathode: attracts the positive copper ions that have a charge of 2+
Anode: loses its copper particles and ions as they’re attracted to the cathode

95
Q

ELECTROLYSIS OF COPPER SULFATE CORE PRACTICAL: How does current impact the rate of electrolysis in the electrolysis of copper sulfate using copper electrodes?

A

As current increases, the rate of electrolysis increases - so the change in mass of electrodes is greater AND VICE VERSA

GCSE Chemistry (9 decks)

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