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Edexcel GCSE Chemistry Triple > TOPIC 3- chemical changes > Flashcards

TOPIC 3- chemical changes Flashcards

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1
Q

Acid

A

Substance w a pH of less than 7. Forms H+ ions in water.

Higher concentration of H+ ions, more acidic

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2
Q

Base

A

A substance that reacts with an acid to produce a salt and water.

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3
Q

Alkali

A

Soluble base that forms hydroxide ions (OH-) in water.

Higher concentration of OH-, higher pH.

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4
Q

Base + Acid&raquo_space;

A

Salt + H2O

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5
Q

Indicator

A

Dye that changes colour depending on whether it’s above/below a certain pH.

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6
Q

How is litmus paper affected by pH?

A

Turns red in acidic solutions, purple in neutral, blue in alkali

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7
Q

How’s is Methyll orange affected by pH?

A

Red in acidic conditions, yellow in neutral/alkaline conditions.

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8
Q

How’s phenolphthalein affected by pH?

A

Colourless in acidic/neutral solutions and pink in alkaline conditions.

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9
Q

Neutralisation

A

Reaction between an acid and a base, producing salt and water.

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10
Q

What are the ions in a neutral solutions?

A

Hydrogen ions are equal to hydroxide ions.

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11
Q

Dissociation of strong acids in water.

A

Ionise almost completely w low pH’s (0-2).

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12
Q

Dissociation of weak acids in water

A

Don’t fully ionise in solution, pH of 4-6.

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13
Q

Acid strength

A

What proportion of acid molecules ionise in water.

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14
Q

Concentration

A

How much acid is in one litre (dm cubed)

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15
Q

How does changing concentration affect pH?

A

Concentration of H+ ions increase by factor of 10 and pH decreases by 1. Opposite effect for decrease in volume.

(Eg decrease of 10p = decrease of 2 pH)

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16
Q

Neutralisation reaction

A

Reaction between an acid and a base

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17
Q

Hydrogen ion

A

H+

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18
Q

Ammonium ion

A

NH4+

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19
Q

Hydroxide ion

A

OH-

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20
Q

Nitrate ion

A

NO3-

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21
Q

Oxide ion

A

O2-

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22
Q

Sulfide ion

A

S2-

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23
Q

Sulfate ion

A

SO42-

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24
Q

Carbonate ion

A

CO32-

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25
Q

Metal+ Acid&raquo_space;

A

Salt + Hydrogen

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26
Q

Test for hydrogen

A

“Squeaky pop” test, putting lighted splint in test tube causes pop.

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27
Q

Carbonate+ acid&raquo_space;

A

Salt+ H2O + CO2

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28
Q

Test for carbon dioxide

A

Bubble through limewater n will turn cloudy.

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29
Q

Solubility of sodium, potassium and ammonium ions

A

Soluble

30
Q

Solubility of nitrates

A

Soluble

31
Q

Solubility of chloride

A

Soluble

Except silver, barium and lead

32
Q

Solubility of common sulfate

A

Soluble (except lead/ barium/ calcium)

33
Q

Solubility of carbonates/ hydroxides

A

Insoluble

Except for sodium, potassium and ammonium

34
Q

Which reaction can be used to make a pure, dry sample of insoluble salt?

A

Precipitation

2 soluble salts

35
Q

Precipitation reaction method to make insoluble salt

A
  1. ) dissolve salts each into separate testubes of deionised water.
  2. ) tip both into a small beaker and stir (precipitate should form)
  3. ) pour through a filtered funnel into conical flask
  4. ) dry remaining precipitate from filter in a dessicator/oven.
36
Q

2 methods of making insoluble salts

A

(Insoluble) Base+ acid&raquo_space; Salt + water

Neutralisation reaction - acid + alkali > salt

37
Q

How are soluble salts made when using a base + acid?

A
  1. ) heat acid in a water bath (speeds up reaction)
  2. ) add insoluble base to the acid (creates soluble salt + water)
  3. ) filter excess solid
  4. ) heat solution gently w b burner and leave to cool and so crystallise
38
Q

Why’s it important to have excess base?

A

So there’s no leftover acid in the product.

39
Q

How are soluble salts made in neutralisation reactions?

A
  1. ) measure set amount of acid into flask w pipette and add indicator.
  2. ) add alkali slowly to acid w burette, mixing until changes colour.
  3. ) carry out reaction w same volumes of alkali and acid (no indicator so is pure).
  4. ) solution left is salt and water which should be evaporated and so left to crystallise. Filter off and dry.
40
Q

Why are titrations used?

A

To find exactly how much acid is needed to neutralise a given quantity of alkali (reversible)

41
Q

What’s concentration measured in?

A

Moles per dm cubed

42
Q

Concentration =

A

Moles number/ solution volume

43
Q

What kind of reaction is the ionisation of a weak acid?

A

Reversible

44
Q

Acid strength

A

What proportion of acid molecules ionise in water.

45
Q

Acid concentration

A

How much acid is in a litre of water.

46
Q

Opposite of concentrated

A

Dilute

47
Q

What happens if H+ ions increase by a factor of ten?

A

Ph decreases by 1

48
Q

Acid + metal hydroxide >

A

Salt + water

49
Q

Acid + metal oxide»

A

Salt + water

50
Q

Electrolysis

A

The breaking down of a substance using electricity.

Electric current is passed through an electrolyte, causing it to decompose.

51
Q

Electrolyte

A

Molten / dissolved ionic compound

52
Q

Cations

A

Positive ions

53
Q

Anions

A

Negative ions

54
Q

Where do cations go?

A

Towards the cathode to be reduced.

55
Q

Cathode

A

Negative electrode

56
Q

Anode

A

Positive electrode

57
Q

Where do anions go?

A

Toward anode to be oxidised.

58
Q

What happens to each ion when they reach an electrode?

A

They are discharged

59
Q

Electrochemical cell

A

A circuit made up of anode, cathode, electrolyte, power source and wires connecting electrodes.

60
Q

How do you set up an electrochemical cell if the electrolyte is a solution?

A

Clean 2 inert electrodes w Emery paper (sandpaper) and place both electrodes in beaker of electrolyte, connected to power supply.

61
Q

How do you set up an electrochemical cell if the electrolyte is a molten ionic substance?

A

Put substance in crucible and heat w Bunsen burner until molten (in fume cupboard).
Dip 2 clean, inert electrodes into electrolyte and connect to power supply.

62
Q

What happens at the cathode in aqueous solutions?

A

Hydrogen and metal ions are present.

Hydrogen gas is produced if metal is more reactive than hydrogen. If metal is less reactive, solid layer of pure metal is produced.

63
Q

What happens at the anode in aqueous solutions?

A

Hydroxide and halide ions are present, therefore molecules of halides are formed.
Oxygen is formed if no halides are present.

64
Q

Solution of copper sulfate ions

A

Cu2+
SO42-
OH-
H+

65
Q

What happens to copper sulphate at cathode w inert electrodes?
Ionic equation?

A

Is less reactive than hydrogen, so is reduced to produce copper metal.
Cu2+ + 2e-&raquo_space; Cu

66
Q

What happens to copper sulphate at anode w inert electrodes?

Ionic equation?

A

No halide ions are present so oxygen is produced and oxidised.

4OH-&raquo_space; 2H2O + O2 + 4e-

67
Q

What happens to the mass of the anode in the electrolysis of copper sulfate with non-inert electrodes?

A

Mass of anode will decrease as copper is transferred from anode to cathode.
Will take longer time (eg 30 mins) to see change in mass

68
Q

What happens to the mass of the cathode in the electrolysis of copper sulfate with non-inert electrodes?

A

It increases as copper is transferred from anode to cathode.

69
Q

How does the electrical supply act in the non-inert electrolysis of copper sulfate?

A

Electrons are pulled off of copper atoms at the anodes and are offered at cathodes to copper ions.

70
Q

How can copper be extracted from its ore?

A

Reduction w carbon

Is impure tho and so electrolysis is used to purify it.

71
Q

What occurs in purification of copper via electrolysis?

A

Impure copper anode is oxidised, forming copper ions in electrolyte.
Ions are then reduced at cathode and are added as layer of pure copper.
Impurities sink to bottom as sludge.

Edexcel GCSE Chemistry Triple (14 decks)

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