Topic 4 - Chemical Changes

Question 1

Describe a neutralisation reaction.

Answer 1

Acid + base -> salt + water

Question 2

When these single indicators are added, what colours do the solutions go to when acid and alkali?

• Litmus
• Methyl orange
• Phenolphthalein

Answer 2

Litmus:
Acid - Red
Alkali - Blue

Methyl orange:
Acid - Red
Alkali - Yellow

Phenolphthalein:
Acid - colourless
Alkali - Pink

Question 3

What are the differences between strong and weak acids?

Answer 3

Strong acids ionise completely in water. Weak acids don’t. The PH of an acid or alkali is the measure of the concentration of H+ ions in the solution. The more acidic, the higher the concentration of H+ ions. Every decrease in the PH scale, increases the concentration by a factor of 10.

Question 4

List the equations for when acids react with:

• metal oxide
• metal hydroxide
• metal carbonate

Answer 4

Acid + metal oxide -> salt + water
Acid + metal hydroxide -> salt + water
Acid + metal carbonate -> salt + water + carbon dioxide

Question 5

List the reactivity series from Potassium to Copper.

Answer 5

Potassium
Sodium
Lithium
Calcium
Magnesium 
Carbon
Zinc
Iron
Hydrogen
Copper

Question 6

What are the equations for when a metal reacts with:

• acid
• water

Answer 6

Metal + acid -> salt + hydrogen

Metal + water -> metal hydroxide + hydrogen

Question 7

What is oxidation and reduction?

Answer 7

Oxidation - gain of oxygen

Reduction - loss of oxygen

Question 8

Some metals can be extracted from their ores chemically by reduction, using carbon. Metals below carbon in the reactivity series can be because the carbon reacts and displaces the other metal, leaving that metal singular and ready for extraction. What happens to metals higher in the reactivity series?

Answer 8

They have to be extracted by electrolysis and that’s expensive.

Question 9

In terms of electrons, what is oxidation and reduction?

Answer 9

Oxidation - loss of electrons

Reduction - gain of electrons

Question 10

Describe electrolysis.

Answer 10

An electric current is passed through an electrolyte. The positive ions will move towards the cathode and the negative ions will move towards the anode. This creates a flow of charge, when they form the uncharged element they are discharged from the electrolyte.