Core Knowledge – Topic 3 Acids

66) What are acids and alkalis sources of?

Answer 66

Acids – hydrogen ions (H+)

Alkalis – hydroxide ions (OH–)

67) What are the colour changes of?

  1. Litmus
  2. Methyl orange
  3. Phenolphthalein

With acid and alkali?

Answer 67

 AcidAlkali
Litmusredblue
Methyl orangeredyellow
Phenolphthaleincolourlesspink

68) What is the link between hydrogen ion concentration and pH?

Answer 68
The higher the concentration of hydrogen ions the lower the pH (a stronger acid). As the hydrogen ion concentration increases by a factor of 10, the pH of the solution decreases by 1.The higher the concentration of hydroxide solutions the higher the pH.

69) When calcium hydroxide is added slowly to hydrochloric acid the pH of the resulting solution changes. What would the graph of this look like?

Answer 69

70) What pH could a concentrated acid have?

Answer 70
Anything between 1 and 6. Acid concentration refers to the dilution with water. A strong acid dissociates completely into ions when dissolved in water and will produce high concentrations of hydrogen ions even when it is of a weak concentration. Conversely a weak acid does not dissociate completely into ions so will have a higher pH even when concentrated.

71) Which would have a pH of 1?

  • 1 mol dm-3 Sulphuric acid (a strong acid)
  • 10 mol dm-3 Ethanoic acid (a weak acid)
Answer 71
Strong acids dissociate completely so will still have a low pH even when dilute.

72) What is a base?

Answer 72
It is a substance that can react with an acid to make a salt and water.

73) What is an alkali?

Answer 73
A soluble base.

74) What type of reaction is it when an acid reacts with a base? 

Answer 74
Neutralisation.

75) What are the products of the following neutralisation reactions?

  1. Metal + acid =
  2. Metal oxide + acid = 
  3. Metal hydroxide + acid =
  4. Metal carbonate + acid =
Answer 75

  1. Salt + hydrogen
  2. Salt + water
  3. Salt + water
  4. Salt + water + carbon dioxide

76) What is the chemical test for?

  1. Hydrogen
  2. Carbon dioxide
Answer 76

  1. Lit splint gives a squeaky pop.
  2. Bubbling carbon dioxide through limewater turns it milky.

77) Explain why water is produced when an acid reacts with an alkali?

Answer 77
The hydrogen ions (H+) from the acid react with the hydroxide ions (OH–) from the alkali to form water (H2O).

78)When preparing a soluble salt from an acid an insoluble reactant how do you ensure the salt is pure?

Answer 33

  1. Use excess insoluble reactant to neutralise all the acid.
  2. Filter the resulting mixture to remove the excess reactant.

79) How do you prepare a soluble salt when both the reactants are soluble?

Answer 79
Titration is used to ensure the reactants are mixed in the correct proportions.

80) How would you prepare a sample of pure, dry hydrated copper sulfate crystals starting from copper oxide.

Answer 80

  1. Add excess copper oxide to sulfuric acid and place in a water bath to gently heat.
  2. Filter the mixture to remove excess copper oxide.
  3. Evaporate the mixture, this can be heated to start with but it must be left to evaporate at room temperature to produce hydrated crystals.

81) How do you carry out an acid-alkali titration, using burette, pipette and a suitable indicator, to prepare a pure, dry sample of sodium chloride?

Answer 81
  1. Fill a burette with hydrochloric acid.
  2. Measure 25 cm3 of sodium hydroxide using a pipette and place in a conical flask.
  3. Add a few drops of phenolphthalein indicator.
  4. Place the conical flask on a white tile underneath the burette.
  5. Run in hydrochloric acid fairly quickly at first whilst continually stirring.
  6. When the neutralisation point is approaching start to add the acid drop wise.
  7. Stop adding the acid the moment the indicator goes clear.
  8. Repeat the titration 2 further times and average results.
  9. Carry out titration one final time, this time without indicator to ensure the salt produced is pure. Stop adding acid when the average quantity previously identified has been added.

82) Are the common sodium, potassium and ammonium salts soluble or insoluble?

Answer 82
soluble.

83) Are nitrates soluble or insoluble?

Answer 83
soluble.

84) Are common chlorides soluble or insoluble? And what is the exception to the rule?

Answer 84
Soluble, except silver chloride and lead chloride.

85) Are common sulfates soluble or insoluble? And what is the exception to the rule?

Answer 85
Soluble, except lead sulphate, barium sulphate and calcium sulphate.

86) Are common carbonates and hydroxides soluble or insoluble? And what is the exception to the rule?

Answer 86
Insoluble, except sodium, potassium and ammonium.

87) What is a precipitate?

Answer 87
A solid formed from two reacting solutions.

88) What is the name of the insoluble precipitate formed when lead nitrate reacts with potassium chloride?

Answer 88
Lead chloride.

89)How do you prepare a pure, dry sample of an insoluble salt?

Answer 89
Mix reacting solutions together in order to get the precipitate, then filter the precipitate out of the solution, wash it with distilled water and dry it.