Acids, bases and salts

Question 1

What are acids?

Answer 1

Substances with a pH of less than 7

Question 2

How can you detect an acid?

Answer 2

They turn litmus paper red or turn universal indicator orange or red.

Question 3

What are bases?

Answer 3

Substances that can react with acids and neutralise them to make a salt and water

Question 4

Give some examples of bases

Answer 4

Copper oxide,

Sodium hydroxide.

Question 5

What are alkalis?

Answer 5

Bases that dissolve in water are called alkalis.

They have a pH of more than 7.

Question 6

How can you detect alkalis?

Answer 6

Alkalis turn red litmus paper blue.
They turn universal indicator paper dark blue or purple if they are strongly alkaline,
and blue-green if they are weakly alkaline.

Question 7

What are neutral solutions?

Answer 7

Neutral solutions have a pH of 7.
They do not change the colour of litmus paper, but they turn universal indicator paper green.
E.g. Water is neutral.

Question 8

What ions are formed when acids dissolve in water?

Answer 8

When acids dissolve in water they produce aqueous hydrogen ions, H+(aq)

Question 9

What does (aq) mean?

Answer 9

(aq) means aqueous (dissolved in water)

Question 10

What happens when alkalis dissolve in water?

Answer 10

When alkalis dissolve in water they produce aqueous hydroxide ions, OH–(aq).

Question 11

What happens when the H+(aq) ions from an acid react with the OH–(aq) ions from an alkali?

Answer 11

A neutralisation reaction occurs to form water:

H+(aq) + OH–(aq) → H2O(l)

Question 12

What happens when acids react with bases?

Answer 12

A salt and water are made

Question 13

Give two examples of an acid reacting with a base

Answer 13

acid + metal oxide → salt + water

acid + metal hydroxide → salt + water

Question 14

Whats the equation for an acid reacting with a metal?

Answer 14

acid + metal → salt + hydrogen

Question 15

What are the second part of the the salt called?

Answer 15

Chloride (if hydrochloric acid is used)
Nitrate (if nitric acid is used)
Sulfate (if sulfuric acid is used)

Question 16

How do you crystallise a salt solution?

Answer 16

If the base dissolves in water, you need to add just enough acid to make a neutral solution.
Warm the salt solution to evaporate the water. You get larger crystals if you evaporate the water slowly.

Question 17

How are insoluble salts made?

Answer 17

They can be made by mixing appropriate solutions of ions together.
Or by reacting together two soluble salts in a precipitation reaction.

Question 18

What does it mean when a salt is insoluble?

Answer 18

The salt doesn’t dissolve in water.

Question 19

What can you use a precipitation reaction for?

Answer 19

Precipitation reactions can be used to remove unwanted ions in solution.
This is useful for treating drinking water and waste water.