C4: Chemical changes

Question 1

What is an ore

Answer 1

COMPOUND OF A METAL FOUND NATURALLY IN ROCKS IN EARTH’S CRUST
A rock containing enough metal to make it economical to extract the metal.

Question 2

What is meant by OXIDISED?

Answer 2

GAINS oxygen, LOSE electrons

Question 3

What is meant by REDUCTION?

Answer 3

LOSE oxygen, GAIN electrons

Question 4

What is a displacement reaction?

Answer 4

A reaction where are more reactive metal takes the place of a less reactive metal in a compound.

Question 5

Metal + oxygen->

Answer 5

Metal oxide

Question 6

Metal +water->

Answer 6

Metal hydroxide + hydrogen

Question 7

How can metals less reactive than carbon be extracted?

Answer 7

Reduction with carbon.
Carbon displaces the metal in the metal oxide and is oxidised to form carbon-oxides.
The metal from the metal oxide gets reduced to the pure metal.

Question 8

What is a redox reaction?

Answer 8

A reaction where both oxidation and reduction occurs.

Question 9

What is a cathode and what is an anode?

Answer 9

Cathode is the negative electrode, anode is the positive electrode

Question 10

What occurs at the cathode and at the anode during electrolysis ?

Answer 10

REDUCTION at cathode
OXIDATION at anode (PANIC)

Question 11

In aqueous electrolysis, who gets made at cathode and anode?

Answer 11

CATHODE- if the metal is more reactive than hydrogen, hydrogen is made. (And vise versa)

ANODE- is the metal is a halide (group7) the halogen gets made, otherwise oxygen is made.

Question 12

How is aluminium manufactured.Why?

Answer 12

Aluminium is made through electrolysis. The main ore of aluminium is bauxite which contain aluminium oxide. This has a VERY high melting point and would be very expensive to melt it because of high energy demand.
Therefore, it is mixed with cryolite this reduces the melting point to about 950C.
Because Al is 3+ it is attracted to the negative electrodes in the cathode and will gain electrons.(this is produced as a liquid on the bottom)
Oxide ions are 2- so they are attracted to the anode where they lose electrons to form oxygen.
Oxygen reacts with the carbon(graphite) anode and produces CO2.

Question 13

Write the half equations for the electrolysis of aluminium

Answer 13

Al3+ + 3e- —> Al
2 O2- —> O2 + 4e-

Question 14

What does aqueous mean?

Answer 14

Dissolved in water

Question 15

Who gets made in the electrolysis of aqueous NaCl ?
Write the half equations.

Answer 15

ANODE- hydrogen because sodium is more reactive

CATHODE- chlorine because it is a halide

2H(+) + 2e- —> H2
2Cl- —> Cl2 + 2e-

Question 16

Why does the positive electrode have to be replaced at regular intervals? (4)

Answer 16

1) electrode is made from carbon
2) 02 is produced at anode
3) 02 reacts with carbon to form c02
4) needs to be replaced as carbon is lost.

Question 17

REQUIRED PRACTICAL : Making soluble salts METHOD (6)
Describe a method to make pure, dry crystals of copper sulphate from a metal oxide and a dilute acid .

Answer 17

1)oxide and sulphuric acid
2)add sulphuric acid to beaker and heat it under a Bunsen burner
3)add copper oxide and stir (CONTINUE ADDING UNTIL COPPER OXIDE IS EXCESS)
4)Filter using filter paper in funnel to remove excess copper oxide
5)heat solution in evaporating basin to crystallisation point (after heating leave rest of water to evaporate slowly to give larger crystals)
6)leave to crystallise

Question 18

REQUIRE PRACTICAL: ELECTROLYSIS

Answer 18

1)Add the aqueous solution to the beaker
2)Add two graphite rods as the electrodes/ put test tubes on electrodes and connect this to a power pack or battery
3)Turn on the power pack or battery and allow electrolysis to take place
4)Record the results in a suitable table and repeat for another solution, checking the electrodes in between runs to see if any metal has been deposited
5)The gases produced can be collected in the test tubes to be tested later

Question 19

Acid + metal —>

Answer 19

Salt + hydrogen

Question 20

Acid + metal oxide —>

Answer 20

Salt + water

Question 21

Acid + metal hydroxide —>

Answer 21

Salt + water

Question 22

Acid + metal carbonate—>

Answer 22

Salt + water + carbon dioxide.