module 6: acids and bases

Question 1

Properties of Acids

Answer 1

Sour
Produce H+ when dissolved in water
pH below 7
Corrosive

Question 2

Properties of Bases

Answer 2

Bitter
Produce OH- when dissolved in water
pH above 7
Caustic

Question 3

Types of Bases

Answer 3

Metal hydroxides
Metal oxides
Metal carbonates/hydrogen carbonates

Question 4

Strength of an acid/base

Answer 4

Extent of ionisation/dissociation in water

Question 5

Strong acids

Answer 5

HCl, HBr, HI, H2SO4, HNO3

Question 6

Strong bases

Answer 6

Group 1 and 2 metal hydroxides

Question 7

Dissociation of an acid

Answer 7

HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)

Question 8

Monoprotic

Answer 8

A substance which is capable of donating one proton (H+)

Question 9

Polyprotic

Answer 9

A substance which is capable of donating multiple protons (H+)

Question 10

Dissociation of a base

Answer 10

B(aq) + H2O(l) ⇌ BH+(aq) + OH-(aq)

Question 11

Methyl orange

Answer 11

Low pH = red
High pH = yellow
pH of colour change = 3.1-4.4

Question 12

Litmus

Answer 12

Low pH = red
High pH = blue
pH of colour change = 4.5-8.3

Question 13

Bromothymol blue

Answer 13

Low pH = yellow
High pH = blue
pH of colour change = 6.0-7.6

Question 14

Phenolphthalein

Answer 14

Low pH = colourless
High pH = pink
pH of colour change = 8.2-10.0

Question 15

Method for Preparing and Testing Cabbage Indicator

Answer 15

1. Shred cabbage leaves, place in beaker, covered with distilled water.
2. Boil cabbage until all red pigment is removed from the leaves.
3. Allow to cool and pour liquid into a clean beaker.
4. Prepare samples of various acids, bases, and neutral substances.
5. Drop cabbage solution into each sample, recording any colour change

Question 16

Limitations of Indicators

Answer 16

Can slightly distort the original pH of solutions
Only provides a range of pH
May change colour at different pH levels is temperature exceeds 25C
The way people observe colour is different

Question 17

Acid-Metal reaction

Answer 17

acid + metal → salt + hydrogen gas

Question 18

Acid-Carbonate reaction

Answer 18

acid + carbonate → salt + water + carbon dioxide

Question 19

Acid-Base reaction

Answer 19

acid + base (hydroxide/oxide) → salt + water

Question 20

Lavoisier’s Theory

Answer 20

(1) An acid is a substance that contains oxygen
(-) Could not explain why metal oxides were not acidic

Question 21

Davy’s Theory

Answer 21

(2) Acids contain replaceable hydrogen, bases neutralise acids
(-) Could not explain why other hydrogen compounds were not acidic

Question 22

Arrhenius Acid

Answer 22

A substance that ionises in water to produce hydrogen ions

Question 23

Arrhenius Base

Answer 23

A substance that dissociates in water to produce hydroxide ions

Question 24

Advantages of Arrhenius Theory

Answer 24

• Explains how neutralisation occurs between acids and bases with the net ionic equation between hydrogen and hydroxide ions
• Explains the relative strength of acids and bases based on their extent of ionisation or dissociation in water

Question 25

Limitations of Arrhenius Theory

Answer 25

• Suggests that non OH containing substances are not a base
• Fails to explain the behaviour of acids and bases in solid or gas phases
• Does not explain why reactions between acids and bases do not produce salt solutions that are neutral