Chemical Changes

Question 1

Define oxidation and reduction in terms of oxygen.

Answer 1

Oxidation - metal gained oxygen.

Reduction - metal lost oxygen.

Question 2

Define oxidation and reduction in terms of electrons.

Answer 2

OIL RIG

Oxidation Is Loss, Reduction is Gain

Question 3

What does an acid + metal form?

Answer 3

salt + water

Question 4

What does an acid + alkali form?

Answer 4

salt + water

Question 5

What does an acid + base form?

Answer 5

salt + water

Question 6

What does an acid + metal carbonate form?

Answer 6

salt + carbon dioxide + water

Question 7

Name 3 acids and their formula?

Answer 7

Hydrochloric acid - HCL
Sulphuric acid - H2SO4
Nitric acid - HNO3

Question 8

What ion is responsible for acidity and alkalinity?

Answer 8

Acidity: Hydrogen ion - H+
Alkalinity: OH-

Question 9

What is the pH of acids, alkalis and neutral and colours on the pH scale?

Answer 9

Alkali - blue to purple, pH 1-6
Acids - red to orange to yellow, pH 8-14
Neutral - green, pH 7

Question 10

What 2 methods can you do to test for pH?

Answer 10

Using universal indicator or a pH probe.

Question 11

What metals can be extracted from their ores using carbon?

Answer 11

Metals such as zinc, iron and copper.

Question 12

What metals have to be extracted from their ores by electrolysis?

Answer 12

Metals that are more reactive than carbon.

Question 13

What is a strong acid?

Answer 13

Completely ionised in aqueous solution.

Question 14

What is a weak acid?

Answer 14

Partially ionised in aqueous solution.

Question 15

How does the strength of an acid relate to pH?

Answer 15

Stronger the acid, lower the pH.

Question 16

What is the relationship between pH and hydrogen ion concentration?

Answer 16

As concentration of H+ ions increases by a factor of 10, the pH value decreases by 1.

Question 17

What happens during electrolysis?

Answer 17

Passing an electric current through the electrolyte causes the ions to move to the electrodes.
+ cathodes go to the cathode.
- cathodes go to the anode.
Ions are discharged at the electrodes to form elements.

Question 18

Does electrolysis require a lot of energy?

Answer 18

Large amounts of energy are used in the extraction process.

Question 19

Why is a mixture used in the electrolysis of aluminium oxide?

Answer 19

Aluminium oxide has a very high melting point, when in a mixture, the melting point is reduced.

Question 20

Why must the positive electrode be constantly replaced in the electrolysis of aluminium oxide?

Answer 20

Because oxygen forms there and reacts with the hot carbon, gradually the carbon anode burns away and needs to be replaced regularly.

Question 21

How can you predict what forms at the anode for electrolysis of aqueous solutions?

Answer 21

Oxygen is produced unless solution contains halide ions when halogen is produced.

Question 22

How can you predict what forms at the cathode for electrolysis of aqueous solutions?

Answer 22

Hydrogen is produced if the metal is more reactive than hydrogen.