C5 Chemical changes

Question 1

State the order of the reactivity series

Answer 1

Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Tin, Lead, Hydrogen, Copper, Silver, Gold

Question 2

What is oxidation?

Answer 2

Loss of electrons

Question 3

What is reduction?

Answer 3

Gain of electrons

Question 4

What is an ionic equation?

Answer 4

Shows only the atoms and ions that change in a reaction

Question 5

What is the general equation for the reaction between a metal and an acid?

Answer 5

metal + acid –> a salt + hydrogen

Question 6

What is the general equation for a neutralisation reaction?

Answer 6

acid + base –> a salt + water

Question 7

The reactions of acids with alkalis

Answer 7

acid + alkali –> a salt + water

Question 8

The reactions of acid with carbonates

Answer 8

acid + a carbonate –> a salt + water + carbon dioxide

Question 9

What are bases?

Answer 9

• Substances that can neutralise acids
• Metal oxides, metal hydroxides, alkalis are bases

Question 10

Examples of strong acids

Answer 10

• Hydrochloric acid
• Nitric acid
• Sulphuric acid

Question 11

Examples of weak acids

Answer 11

• Ethanoic acid
• Citric acid
• Carbonic acid

Question 12

What are strong acids?

Answer 12

• Ionise completely in solution
• Produce solutions with a high concentration of H+ ions and thus a very low pH

Question 13

What are weak acids?

Answer 13

• Only partially ionise in water
• Producing solutions of pH values between 4-6

Question 14

pH

Answer 14

A measure of the hydrogen ion (H+) concentration, a low pH means a high concentration of H+ ions

Question 15

Examples of strong alkalis

Answer 15

Sodium and potassium hydroxide

Question 16

Example of weak alkalis

Answer 16

Ammonia solution

Question 17

Describe a method to make pure, dry crystals of magnesium sulphate from a metal oxide

Answer 17

• Measure out 10cm^3 of sulphuric acid into a beaker. Heat for one minute
• Add small amounts of magnesium oxide at a time, whilst stirring, until no more dissolves and fizzing stops (until magnesium oxide is in excess)
• Filter off excess magnesium oxide and collect filtrate in an evaporating basin
• Evaporate half the water and leave to crystallise
• Pat dry with filter paper

Question 18

What happens in displacement reactions?

Answer 18

A more reactive metal will displace a less reactive metal from an aqueous solution of one of its salts

Question 19

How to make pure, dry samples of a named soluble salt

Answer 19

• Carry out a titration with the indicator added to see how much acid reacts completely with the alkali
• Run that volume of acid into the solution of acid again, but this time without the indicator
• Then crystals and dry the crystals of salt from the reaction mixture

Question 20

How are pH values related to the concentration of H+ ions?

Answer 20

As the concentration of H+ ions decreases by a factor of 10, the pH value increases by one unit