Acids and Bases

Question 1

What does the pH scale measure?

Answer 1

How acidic or alkaline a solution is.

Question 2

What is the pH range for acidic, neutral and alkaline solutions?

Answer 2

Acid: below 7, Neutral: 7, Alkaline: above 7.

Question 3

What type of ions do acids form in water?

Answer 3

H⁺ (hydrogen) ions.

Question 4

What type of ions do alkalis form in water?

Answer 4

OH⁻ (hydroxide) ions.

Question 5

What is a base?

Answer 5

A substance that neutralises an acid.

Question 6

Name three common bases.

Answer 6

Metal oxides, metal hydroxides, metal carbonates.

Question 7

What is an alkali?

Answer 7

A soluble base (dissolves in water).

Question 8

How can you make an acidic solution?

Answer 8

Dissolve a non-metal oxide in water (e.g., SO₂).

Question 9

How can you make an alkaline solution?

Answer 9

Dissolve a soluble metal oxide or hydroxide in water (e.g., Na₂O + H₂O → NaOH).

Question 10

How does concentration of H⁺ ions affect pH?

Answer 10

Higher H⁺ → lower pH → more acidic.

Question 11

How does concentration of OH⁻ ions affect pH?

Answer 11

Higher OH⁻ → higher pH → more alkaline.

Question 12

What happens to pH when you dilute an acid?

Answer 12

pH increases towards 7.

Question 13

What happens to pH when you dilute an alkali?

Answer 13

pH decreases towards 7.

Question 14

Why is pure water neutral?

Answer 14

It contains equal concentrations of H⁺ and OH⁻ ions.

Question 15

What is neutralisation?

Answer 15

Acid + base → salt + water.

Question 16

What is produced in a neutralisation reaction?

Answer 16

A salt and water.

Question 17

What salt do hydrochloric, sulfuric and nitric acids make?

Answer 17

Hydrochloric → chloride, Sulfuric → sulfate, Nitric → nitrate.

Question 18

What do acids + metal oxides/hydroxides make?

Answer 18

Salt + water.

Question 19

What do acids + metal carbonates make?

Answer 19

: Salt + water + carbon dioxide.

Question 20

What is a spectator ion?

Answer 20

An ion that doesn’t change in the reaction — stays the same on both sides.

Question 21

What is an ionic equation?

Answer 21

An equation that shows only the ions that react, not the spectator ions.

Question 22

What is titration used for?

Answer 22

To find the exact volume of acid needed to neutralise an alkali (or vice versa).

Question 23

What piece of equipment is used to add acid in small amounts during titration?

Answer 23

A burette.

Question 24

What piece of equipment is used to measure a fixed volume of alkali?

Answer 24

A pipette.

Question 25

What shows when the alkali has been neutralised?

Answer 25

: The indicator changes colour.

Question 26

What is meant by the ‘end-point’ of a titration?

Answer 26

The point where the indicator changes colour, showing neutralisation.

Question 27

What are concordant results?

Answer 27

Two or more results within 0.2 cm³ of each other.

Question 28

What should you do to get accurate titration results?

Answer 28

Repeat the experiment and calculate the mean of concordant results.

Question 29

What is a soluble salt?

Answer 29

A salt that dissolves in water.

Question 30

What is an insoluble salt?

Answer 30

A salt that does not dissolve in water and forms a solid (precipitate).

Question 31

What is a precipitation reaction?

Answer 31

A reaction where two solutions form an insoluble salt as a solid.

Question 32

What does a precipitate look like?

Answer 32

A solid that appears in a solution after a reaction.

Question 33

What are two examples of soluble solutions that can make lead iodide?

Answer 33

Lead nitrate and sodium iodide.

Question 34

What does the solubility of a salt depend on?

Answer 34

Whether its ions form soluble or insoluble compounds.

Question 35

What are the steps to make an insoluble salt like lead iodide?

Answer 35

Dissolve lead nitrate and sodium iodide in water Mix them to form a yellow precipitate Filter out the solid using filter paper and funnel Wash and dry the solid

Question 36

What is the filter paper used for in salt-making?

Answer 36

To separate the solid (insoluble salt) from the solution.

Question 37

Why do we wash the solid with deionised water?

Answer 37

To remove any soluble impurities.

Question 38

How do you make a soluble salt using an acid and an insoluble base?

Answer 38

Warm the acid Add the base until no more reacts (excess) Filter off the excess base Evaporate water to crystallise the salt

Question 39

What are good examples of insoluble bases?

Answer 39

Metal oxide, metal hydroxide, metal carbonate.

Question 40

Why is the acid heated in the salt-making process?

Answer 40

To speed up the reaction.

Question 41

Why is excess base used in salt-making?

Answer 41

To make sure all the acid has reacted.

Question 42

Why is the excess base filtered out?

Answer 42

So the final solution only contains salt and water — not unreacted base.

Question 43

Why can't you see when an acid and alkali reaction is finished?

Answer 43

Because both are colourless, and there’s no visible signal.

Question 44

How do you know when the acid and alkali have neutralised each other?

Answer 44

Use an indicator to show the end-point (colour change).

Question 45

What is the general method for making a soluble salt using acid and alkali?

Answer 45

Add acid to alkali using a burette with indicator Stop at end-point Repeat using same volumes without indicator Evaporate solution to get pure dry salt

Question 46

Why must the indicator not be in the final salt product?

Answer 46

It would contaminate the salt.

Question 47

What does evaporation do in the salt-making process?

Answer 47

It removes water, leaving behind solid salt crystals.