C5: Chemical Changes

Question 1

What are displacement reactions?

Answer 1

When a more reactive element displaces a less reactive one from its compound.

Question 2

How are different metals extracted?

Answer 2

A metal ore contains enough of the metal to make it economic to extract it so are mined and purified, such as gold and other unreactive metals.
Oxides of metals below carbon in reactivity series extracted by reduction with carbon.
Metals above carbon are extracted by electrolysis.

Question 3

What is metal + acid?

Answer 3

Metal + Acid —> Salt + Hydrogen
(Redox reaction)

Question 4

What types of salts are produced with different acids?

Answer 4

Hydrochloric acid produces chlorides.
Nitric acid produces nitrates.
Sulfuric acid produces sulfates.

Question 5

What are bases?

Answer 5

Insoluble metal hydroxides/oxides that neutralise acids.

Question 6

What is acid + base?

Answer 6

Acid + Base —> Salt + Water

Question 7

What is acid + metal carbonate?

Answer 7

Acid + Metal Carbonate —> Salt + Water + Carbon Dioxide

Question 8

How do you make salts using an acid and base?

Answer 8

1. Measure 20cm3 of acid into a measuring cylinder and pour it into a beaker.
2. Heat gently using a bunsen burner. (Tripod, gauze, heatproof mat).
3. Using a spatula, add small amounts of insoluble base (e.g. copper oxide) in excess and stir until no more reacts. Shown when no more dissolves.
4. Allow to cool then filter the solution using filter paper and funnel to remove excess base.
5. Pour solution into evaporating basin.
6. Place on a beaker half filled with water on gauze on tripod above bunsen burner to evaporate solution until crystals start to form.
7. Leave evaporating basin in cool place for 24 hours to let water evaporate slowly, gently pat crystals dry with filter paper.

Question 9

How do you collect salt crystals using acid and alkali?

Answer 9

Carry oyt titration to see how much acid is needed to completely react, run that volume of acid into alkali then crystallise using evaporating basin.

Question 10

What is the ionic equation for neutralisation?

Answer 10

H+(aq) + OH-(aq) —> H2O(l)

Question 11

What is the difference between strong and weak acids?

Answer 11

Strong acids completely ionise in aqueous solutions and have a lower pH. Weak acids only partially ionise.

Question 12

What happens as pH decreases?

Answer 12

As pH decreases by 1 unit, H+ concentration increases by a factor of 10.