Chemical Changes

Question 1

What is oxidation/reduction?

Answer 1

Oxidation - When a substance gains oxygen
Reduction - When a substance loses oxygen

Question 2

What is the reactivity series of metals?

Answer 2

The series shows the metals in order of their reactivity.

Question 3

What are the trends in
reactivities of metals in reactions with acids/water?

Answer 3

Metals above H2
in reactivity series react with acid to produce H2
. The more
reactive the metal is, the quicker and more violent reaction with acid occurs.
Metals below H2
don’t react with acids.
Not all metals above H2
react with water - mostly Group I and II metals. Aluminium
is the borderline case.

Question 4

What is a displacement reaction?

Answer 4

A reaction where a more reactive metal displaces a less reactive metal from a
compound

Question 5

How are unreactive metals found in Earth?

Answer 5

In their natural state

Question 6

How can metals less reactive than carbon be extracted?

Answer 6

Reduction with carbon. Carbon displaces the metal in a metal oxide - gets
oxidised to carbon oxides. Metal from the metal oxide gets reduced to the pure
metal.

Question 7

How are oxidation and reduction defined in terms of electron
transfer?

Answer 7

Oxidation – loss of electrons
Reduction – gain of electrons

Question 8

What is the general equation for a reaction between metals
and acids?

Answer 8

Metal + acid → salt + hydrogen

Question 9

Which metals in the reactivity series will react with acid?

Answer 9

Those above hydrogen

Question 10

What is the general equation for a neutralisation reaction?

Answer 10

Base + acid → salt + water

Question 11

What is a redox reaction?

Answer 11

A reaction where both oxidation and reduction occurs

Question 12

How is a soluble salt formed?

Answer 12

a) React the excess acid with some insoluble chemical (e.g. metal oxide)
b) Filter off the leftovers
c) Crystallise the product

Question 13

What do acids and alkalis produce in aqueous solutions

Answer 13

Acids produce hydrogen ions, alkalis produce hydroxide ions

Question 14

What are bases, acids and alkalis?

Answer 14

Bases are compounds that neutralise acids, acids produce hydrogen ions in
aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous
solutions

Question 15

What is a strong acid and weak acid?

Answer 15

Strong acid is completely ionised in aqueous solution; weak acid is only partially
ionised in aqueous solution

Question 16

Name the following salts: LiNO3
, K2CO3
, MgBr2
,
BaSO4

Answer 16

Lithium nitrate
Potassium carbonate
Magnesium bromide
Barium sulphate

Question 17

What is electrolysis?

Answer 17

The passing of an electric current through ionic substances that are molten or in
solution to break them down into elements; ions are discharged (they lose/gain
electrons) at electrodes to produce these

Question 18

What is an electrolyte?

Answer 18

The liquid/solution which conducts electricity

Question 19

What is a cathode and what is an anode?

Answer 19

Cathode is the negative electrode, anode is the positive electrode

Question 20

How is aluminium manufactured? Why is it expensive?

Answer 20

Aluminium is made through the electrolysis of aluminium oxide and cryolite.
Lots of energy is needed to produce the current in electrolysis which makes this
process expensive.

Question 21

What are the half equations in the extraction of aluminium?

Answer 21

Al3+ + 3 e−
→ Al (cathode)
2 O2− → O2
+ 4 e− (anode)
Oxygen reacts with C of the anode producing CO2
.

Question 22

Why is cryolite used in manufacturing of aluminium?

Answer 22

It lowers the melting point of aluminium oxide, reducing energy costs

Question 23

What are the half equations in electrolysis of the
aqueous Na2SO4
?

Answer 23

2 H+
+ 2 e−
→ H2
(cathode)
4 OH−
→ 2 H2O + O2
+ 4 e− (anode)

Question 24

What are the half equations in electrolysis of the
molten and aqueous KCl?

Answer 24

K
+
+ e−
→ K (cathode)
2 Cl−
→ Cl2
+ 2 e− (anode)
2 H+
+ 2 e−
→ H2
(cathode)
2 O2− → O2
+ 4 e− (anode)

Question 25

What are the half equations in electrolysis of the
aqueous CuBr2
?

Answer 25

Cu2+ + 2 e−
→ Cu (cathode)
2 Br−
→ Br2
+ 2 e− (anode)