Acids and Bases

Question 1

Acid

Answer 1

A substance that dissociates in water to form hydrogen ions, H+ (aq).

Question 2

Monobasic

Answer 2

1 molecule produces 1 hydrogen ion upon dissociation

Question 3

Dibasic

Answer 3

1 molecule produces 2 hydrogen ions upon dissociation

Question 4

Tribasic

Answer 4

1 molecule produces 3 hydrogen ions upon dissociation

Question 5

Physical properties of acids

Answer 5

1. Acids have a sour taste.
2. Acids have pH less than 7 (green to yellow or orange or red, increasing acidity)
3. Acids are good conductor of electricity in aqueous solution as they contain mobile ions to act as mobile charge carriers

Question 6

Chemical properties of acid

Answer 6

1. Acid reacts with reactive metal to form a salt and hydrogen gas.
2. Acid reacts with bases to form a salt and water only. (Neutralisation)
3. Acids react with carbonates to form a salt, carbon dioxide and water.

Question 7

Uses of acids

Answer 7

H2SO4: in making detergent, fertilisers, car batteries
Ethanoic acid: preserve food, making adhesives such as glue
Hydrochloric acid: in leather processing and cleaning metals

Question 8

Base

Answer 8

Any metal oxide or hydroxide that reacts with acids to produce salt and water only.

Question 9

Alkali

Answer 9

A soluble base that dissociates in water to produce hydroxide ions

Question 10

Physical properties of alkali

Answer 10

1. They have bitter taste and soapy feel.
2. Alkalis have pH greater than 7 (turns universal indicator from green to blue or violet)
3. Alkalis are good conductor of electricity in aqueous solution as they contain mobile ions

Question 11

Chemical properties of alkalis

Answer 11

1. They react with acids to form a salt and water only.
2. Alkalis are heated with ammonium salt to give off ammonia gas
3. Alkali reacts with a solution of one metal salt to give salt and metal hydroxide

Question 12

Uses of bases

Answer 12

Magnesium oxide: relieving gastric pain and for making refractory bricks
Sodium hydroxide/potassium hydroxide: used in preparation of soap
Calcium oxide/Calcium hydroxide: reduce acidity in the soil
Ammonia solution: used in making fertiliser

Question 13

Concentration of an acid/alkali

Answer 13

Amount of acid/alkali dissolved in 1 dm^3 of water

Question 14

Indicators

Answer 14

1. Universal indicator
2. pH meter (pH probe attached to a data logger)
3. Methyl orange: red (acid) yellow (alkali)
4. Phenolphthalein: colourless (acid) pink (alkali)

Question 15

Bases cannot be used with ammonium- based fertiliser.

Answer 15

They react with ammonium salt to form ammonia gas which escapes into the atmosphere. Thus, the plants cannot absorb the ammonium ion which provides the nitrogen it needs. Calcium oxide/hydroxide which is required to neutralise the soil acidity is also lost