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Chemistry GCSE Paper 1 > 4. Chemical Changes > Flashcards

4. Chemical Changes Flashcards

1
Q

What is the pH scale?

A

The measure of how acidic or alkaline a solution is.

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2
Q

What pH is a neutral substance?

A

pH 7.

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3
Q

What pH is car battery acid and stomach acid?

A

pH 1.

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4
Q

What is pH of vinegar and lemon juice?

A

pH 3.

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5
Q

What is the pH of acid rain?

A

pH 4.

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6
Q

What is the pH of normal rain?

A

pH 5.

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7
Q

What is the pH of washing up liquid?

A

pH 8/9.

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8
Q

What is the pH of pancreatic juice?

A

pH 10.

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9
Q

What is the pH of soap powder?

A

pH 11.

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10
Q

What is the pH of bleach?

A

pH 12.

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11
Q

What is the pH of caustic soda?

A

pH 12/14.

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12
Q

What is an indicator?

A

A dye that changes colour depeneding on whether it’s above or below a certaini pH.

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13
Q

What are wide range indicators?

A

Contain a mixture of dyes that can gradually change colour over a broad range of pH. Useful for estimating the pH of a soution, eg. universal indicator.

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14
Q

What is a pH probe?

A

Attached to a pH meter which can measure pH electronically. Gives a numerical pH value meaning it’s more accurate.

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15
Q

What is an acid?

A

Substance that forms aqueous solution with a pH less than 7. Form H+ ions in water.

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16
Q

What is a base?

A

Substance with a pH greater than 7.

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17
Q

What is an alkali?

A

A base that dissolves in water to form solution with a pH greter than 7. Forms OH- ions in water.

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18
Q

What is neutralisation?

A

The reaction between acids and bases.

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19
Q

What is the word equation for neutralisation?

A

acid + base ⇨ salt + water.

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20
Q

What is the symbol equation for neutralisation between acids and alkalis?

A

H+ (aq) + OH- (aq) ⇨ H₂O (l).

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21
Q

How would you carry out a titration practical?

A

Finding the concentration of an alkali:

  1. Using a pipette and pipette filler, add a set volume of alkali to a conical flask. Add two or three drops of indicator.
  2. Use a funnel to fill a burette with acid of a know concentration. Record the initial volume of the burette.
  3. Using a burette, add the acid to the alkali a bit at a time, giving the conical flask a regualar swirl. Go slowly when near the end-point.
  4. The indicator changes colour when all the alkali has been neutralised.
  5. Record the final volumes of acid in the burette. Use this to calculate the volume needed to neutralise the alkali.
  6. Calculate a mean.
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22
Q

What indicators could be used in titrations?

A
  1. Litmus (blue in alkalis, red in acids).
  2. Phenolphthalein (pink in alkalis, colourless in acids).
  3. Methyl orange (yellow in alkalis, red in acids).
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23
Q

What is a strong acid?

A

One that ionises completely in water. All acid particles dissociate to release H+ ions.

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24
Q

What is a weak acid?

A

One that doesn’t fully ionise in solution. Only a small proportion of acid particles dissociate to release H+ ions. The ionisation of a weak acid is a reversible reaction, which sets up an equilibrium between the undissociated and dissociated acid. Since only a few of the acid particles release H+ ions, the position of equilibrium lies well to the left.

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25
Q

Why are strong acids more reactive than weak acids?

A

They have a higher concentration of H+ ions, so the rate of reaction will be faster.

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26
Q

What is pH?

A

The measure of the concentration of H+ ions in the solution.

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27
Q

For every decrease of 1 on the pH scale, the concentration of H+ ions increases by a factor of __?

A
  1. Factor H+ ion concentration changes by = 10⁻ˣ.
28
Q

What does acid strength tell you?

A

What proportion of the acid molecules ionise in water.

29
Q

What does concentration of an acid tell you?

A

How much acid there is in a certain volume of water.

30
Q

Acid + Metal oxide ⇨ ?

A

Salt + water.

31
Q

Acid + Metal Hydroxide ⇨ ?

A

Salt + water.

32
Q

Acid + Metal Carbonate ⇨ ?

A

Salt + water + carbon dioxide.

33
Q

How can you make soluble salts using a soluble base?

A
  1. Warm the dilute acid using a bunsen burner, then turn it off.
  2. Add the insoluble base to the acid a bit at a time, until no more reacts (base in excess). The excess solid will sink to the bottom of the flask.
  3. Filter the excess solid to get the salt solution.
  4. Heat the solution using a water bath or electric heater to evaporate the water and stop heating and leave it to cool. Crystals should start to form which will be filtered out of the solution and dried (crystallisation).
34
Q

What is the reactivity series?

A

Lists metals in order of their reactivity towards other substances.

35
Q

What is the reactivity series determined by?

A

How easily the metals lose electrons.

36
Q

How could you order the metals?

A

Comparing the relative reactivity of different metals wih either acid or water. Temperature change.

37
Q

Acid + Metal ⇨ ?

A

Salt + Hydrogen.

38
Q

What indicated the speed of a reaction?

A

The rate at which the bubbles of hydrogen are given off.

39
Q

Metal + Water ⇨ ?

A

Metal + water ⇨ metal hydroxide + hydrogen.

40
Q

What is oxidation?

A

Gaining of oxygen. (Formation of metal ore).

41
Q

What is reduction?

A

Loss of oxygen. (Extraction of metal).

42
Q

How can metals below carbon in the reactivity series be extracted from their ores?

A

Reducing them with carbon.

43
Q

What is oxidation in terms of electrons?

A

Loss of electrons.

44
Q

What is reduction in terms of electrons?

A

Gain of electrons.

45
Q

What is a redox reaction?

A

When reduction and oxidation happen at the same time.

46
Q

What is a displacement reaction?

A

When a more reactive metal will displace a less reactive metal in a compound.

47
Q

What is electrolysis?

A

Electric current is passed through an electrolyte. The ions move towards the electrode, where they react and the compound decomposes.

48
Q

Where do the positive ions move?

A

The cathode (-ve electrode), where they are reduced.

49
Q

Where do the negative electrons go?

A

The anode (+ve electrode), where they are oxidised.

50
Q

Why can’t an ionic solid be electrolysed?

A

The ions are in fixed positions and can’t move.

51
Q

Why can molten ionic compounds be electrolysed?

A

The ions can move freely and conduct electricity.

52
Q

When would electrolysis be used?

A

When a metal is too reactive to be displaced with carbon.

53
Q

Why is electrolysis expensive?

A

Lots of energy is required to melt the ore and produce the required current.

54
Q

What ore is aluminium extracted from?

A

Bauxite (contains aluminium oxide).

55
Q

What is aluminium oxide mixed with to lower the melting point?

A

Cryolite.

56
Q

What happens to the Al³⁺ ions during electrolysis of molten Aluminum Oxide?

A

They are attracted to the negative electrode where they pick up three electrons and turn into neutral aluminium atoms. These then sink to the bottom of the electrolysis tank.

57
Q

What happens to the O²⁻ ions during electrolysis of molten Aluminum Oxide?

A

They are attracted to the positive electrodw where they lose two electrons. The neutral oxygen atoms combine to from O₂ molecules.

58
Q

What is the equation at the cathode electrolysis of molten aluminum oxide?

A

Al³⁺ + 3e⁻ ⇨ Al.

59
Q

What is the equation at the anode electrolysis of molten aluminum oxide?

A

2O²⁻ ⇨ O₂ + 4e⁻.

60
Q

What other ions will there be in the water in aqueous solutions?

A

Hydrogen ions (H+) and hydroxide ions (OH-).

61
Q

What will be formed at the cathode of electrolysis of aqueous solutions?

A

If H+ and metal ions are present, hydrogen gas will be produced if the metal ions from an element metal that is more reactive than hydrogen.

62
Q

What will be formed at the anode of electrolysis of aqueous solutions?

A

If OH- and halide ions are present, molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, then the OH- ions are discharged and oxygen will be formed.

63
Q

How can you test for chlorine?

A

Bleaches damp litmus paper, turning it white.

64
Q

How can you test for hydrogen?

A

Makes a squeaky pop sound with a lighted splint.

65
Q

How can you test for oxygen?

A

Will relight a glowing splint.

Chemistry GCSE Paper 1 (5 decks)

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