Topic 4 Key Concepts Summary

Question 1

metal + oxygen

Answer 1

metal oxide

Question 2

metal + water

Answer 2

metal hydroxide + hydrogen

Question 3

metal + acid

Answer 3

→ salt + hydrogen

Question 4

acid + base

Answer 4

→ salt + water

Question 5

How do you make soluble salt from acids and insoluble reactants (Practical)

Answer 5

From acids and insoluble reactants
1. excess of the reactant (a metal, metal oxide, or metal carbonate) is
added and gently heated to make sure all of the acid reacts.
2. The excess reactant has to be removed by filtration.
3. Evaporate half the water from the filtrate and leave in a warm place
to slowly evaporate and to ‘grow’ the crystals.
4. Remove any liquid using paper towel to produce dry crystals of salt

Question 6

How do you make soluble salt from acids and soluble reactants (Practical)

Answer 6

From acids and soluble reactants
1. Titration must be used because there is no insoluble excess reactant
that we can remove using filtration
2. the acid and the soluble reactant (usually a dilute alkali) are mixed in
the correct proportions.
3. Follow step 3 above

Question 7

The positive electrode (anode) made from graphite (C) must be regularly replaced because…

Answer 7

The positive electrode (anode) made
from graphite (C) must be regularly
replaced because it reacts with the O2
C(s) + O2
(g) ⟶ CO2
(g)

Question 8

Required Practical – Energy Changes

Answer 8

Required practical: measuring energy
change: neutralisation
1. put polystyrene cup in a beaker for
insulation and support
2. measure required volume of
hydrochloric acid with
measuring cylinder
3. clamp thermometer into place
making sure the thermometer bulb is
immersed in liquid
4. measure the initial temperature of
the acid
5. add 5cm3 of sodium hydroxide.
6. stirs mixture and measure
temperature
7. repeat steps 5 and 6 until 40cm3 of
NaOH is added

Question 9

What happens to oxygen inside an acidic fuel cell?

Answer 9

The fuel is oxidised electrochemically within the fuel cell
to produce a potential difference.

Question 10

What is the overall reaction inside a fuel cell?

Answer 10

The overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce water.
Hydrogen + oxygen → water
2H2 + O2 → 2H2O

Question 11

How does an acidic fuel cell work?

Answer 11

The fuel cell consists of an electrolyte and porous carbon electrodes coated with a catalyst.
Hydrogen enters at the anode where it is oxidised and oxygen enters at the cathode where it is reduced

Question 12

What are the reaction at the anode, cathode and overall in an acidic fuel cell?

Answer 12

Reaction at anode (-): OXIDATION
2H2 → 4H+ + 4e–
Reaction at cathode (+): REDUCTION
4H+ + O2 + 4e– → 2H2O
The overall reaction is:
2H2 + O2→ 2H2O

Question 13

What happens in an anlkaline fuel cell?

Answer 13

Hydrogen enters at the anode where it
reacts with hydroxide ions to produce
water. This produces electrons.
Reaction at anode (-): OXIDATION
2H2 +4OH- → 4e- + 4H2O
Oxygen enters at the cathode where it
reacts with water to produce hydroxide
ions. This uses up electrons.
Reaction at cathode (+): REDUCTION
4e- + 2H2O +O2 → 4OHThe overall reaction is:
2H2 + O2→ 2H2O
The electrons move around the external
circuit from the cathode to the anode
which drives an electric motor.