C8. Acids, bases and salts

Question 1

What is the pH scale range for acids?

Answer 1

1 - 6

Question 2

What is the pH scale for neutral?

Answer 2

7

Question 3

What is the pH scale for bases?

Answer 3

8 - 14

Question 4

What are ‘acids’?

Answer 4

A compound which produces hydrogen ions when dissolved in water.

Question 5

Name the reactions of dilute acids.

Answer 5

• Metal + acid -> salt + hydrogen
• Metal pxides + acid -> salt + water
• Carbonates + acid -> salt + water + carbon dioxide

Question 6

What is a ‘base’?

Answer 6

A substance that can neutralise an acid.

Question 7

What is an ‘alkali’?

Answer 7

A soluble base.

Question 8

Name the reactions of bases with acids.

Answer 8

• Base + acid -> salt + water

Question 9

What are ‘oxides’?

Answer 9

Compounds of metals or non-metals with oxygen.

Question 10

How are acidic oxides formed?

Answer 10

Non-metals reacting with oxygen.

Question 11

How are basic oxides formed?

Answer 11

Metals reacting with oxygen.

Question 12

How do we make salts?

Answer 12

• Reacting a metal with an acid
• Reacting an insoluble base with an acid
• Neutralising an alkali with an acid by the titration method
• By precipitation

Question 13

What are the conditions for making salts from metals?

Answer 13

Only for metals above hydrogen in the reactivity series.

Question 14

How do we make salts from metals?

Answer 14

• Add the metal to the acid in a flask so that the metal is in excess.
• Warm the flask gently to complete the reaction.
• Filter off the excess metal.
• Put the filtrate into an evaporating basin and evaporate the water until the crystallisation point is reached; allow salt to crystallise at room temp.
• Filter off the crystals and wash them with a tiny amount of solvent so they don’t dissolve.
• Dry the crystals between sheets of filter paper.

Question 15

How to make salts from insoluble bases?

Answer 15

By reacting an insoluble base with an acid.

Only for metals that are low in the reactivity series.

Question 16

How to test for hydrogen?

Answer 16

Lighted splint at the mouth of the test tube -> squeaky pop

Question 17

How to test for oxygen?

Answer 17

Glowing splint into the test tube -> splint relights

Question 18

How to test for ammonia?

Answer 18

Holds a damp red litmus paper at the mouth of the test tube -> turns red litmus blue

Question 19

How to test for carbon dioxide?

Answer 19

Limewater -> turns cloudy/milky

Question 20

How to test for chlorine?

Answer 20

Damp litmus paper at the mouth of the test tube -> paper turns white - bleached

Question 21

How to test for sulfur dioxide?

Answer 21

Potassium mangante(VII), which is purple -> turns the liquid colourless

Question 22

Tests for cations by means for aqueous sodium hydroxide:

• ammonium
• copper(II)
• iron(II)
• iron(III)
• zinc

Answer 22

Ammonium: white precipitate
Copper: light blue precipitate
Iron(II): grey-green precipitate
Iron(III): reddish-brown precipitate
Zinc: white precipitate

Question 23

Tests for cations by means for aqueous ammonia:

• ammonium
• copper(II)
• iron(II)
• iron(III)
• zinc

Answer 23

Ammonium: white precipitate
Copper: light blue precipitate
Iron(II): grey-green precipitate
Iron(III): reddish-brown precipitate
Zinc: white precipitate

Question 24

How to identify carbonates?

Answer 24

Adding a dilute acid to an unknown compound then testing the gas produced with limewater.

Question 25

How to identify halides/chloride?

Answer 25

Aqueous silver nitrate under acidic conditions.

Question 26

How to identify nitrates?

Answer 26

Adding sodium hydroxide and aluminium foil, warming gently, then test for the release of ammonia gas.

Question 27

How to identify sulfates?

Answer 27

Adding acidified barium chloride to the unknown compound -> white precipitate

Question 28

How to identify sulfites?

Answer 28

Adding dilute hydrochloric acid, warming and testing for sulfur dioxide.