Section 3 - Cemical Changes

Question 1

What is the pH scale?

Answer 1

A measure of how alkaline or acidic a solution is.

Question 2

Where are acids on the pH scale?

Answer 2

Below 7.

Question 3

Where are alkalis on the pH scale?

Answer 3

Above 7.

Question 4

What is a base?

Answer 4

A substance that reacts with an acid to make a salt.

Question 5

What is an acid?

Answer 5

A substance that reacts with base to make a salt.

Question 6

What is an alkali?

Answer 6

A base that is soluble in water.

Question 7

How can pH be measured?

Answer 7

Using indicators or electronic testing devices.

Question 8

How does the concentration of hydrogen change through the pH scale?

Answer 8

The lower the pH the higher the concentration of hydrogen.

Question 9

Where is neutral on the pH scale?

Answer 9

7

Question 10

What is an Indicator?

Answer 10

A dye that changes colour due to pH.

Question 11

What colours does universal indicator become? At what pHs?

Answer 11

Reds in acidic solutions, green when neutral and purple when alkaline.

Question 12

What colours does litmus become? At what pHs?

Answer 12

Red in acids, purple when neutral and blue when alkaline.

Question 13

What colours does methyl orange become? At what pHs?

Answer 13

Red in acids and yellow when neutral.

Question 14

What colours does phenolphthalein become? At what pHs?

Answer 14

Colourless and clear in acidic or neutral solutions but pink in alkalis.

Question 15

What is the reaction between an acid and a base called?

Answer 15

Neutralisation.

Question 16

Where do neutralisation reactions occur?

Answer 16

In aqueous solutions.

Question 17

What are the products of neutralisation? What pHs are they?

Answer 17

Salts and water, both are a pH of 7.

Question 18

What do all acids do in water?

Answer 18

Ionise, or dissociate, forming a hydrogen ion and another ion.

Question 19

What does an acid’s strength mean?

Answer 19

What proportion of the acid molecules ionise in water.

Question 20

If an acid is weak, what does it mean?

Answer 20

A small proportion of the acid molecules ionise in water.

Question 21

If an acid is strong, what does it mean?

Answer 21

A large proportion of the acid molecules ionise in water.

Question 22

What type of reaction is the ionisation of a weak acid? What does this form?

Answer 22

The reaction is reversible, this creates an equilibrium.

Question 23

What is concentration in acids?

Answer 23

The amount of acid per litre.

Question 24

How does an acids concentration effects its pH?

Answer 24

If the concentration of hydrogen ions changes by a factor of ten, the pH changes by one inversely.

Question 25

What happens when a metal reacts with an acid?

Answer 25

It produces salt and hydrogen.

Question 26

What happens when a metal carbonate reacts with an acid?

Answer 26

It produces salt, water and carbon dioxide.

Question 27

How can carbon dioxide be tested for using limewater?

Answer 27

The limewater changes colour from clear to cloudy yellow when carbon dioxide is bubbled through it.

Question 28

Are common chlorides soluble?

Answer 28

Yes, except silver chloride and lead chloride.

Question 29

Are common sulfates soluble?

Answer 29

Yes, except lead, barium and calcium sulfate.

Question 30

Are common carbonates and hydroxides soluble?

Answer 30

No, except those of sodium, potassium and ammonium.

Question 31

Are common salts of sodium potassium and ammonium soluble.

Answer 31

Yes.

Question 32

Are nitrates soluble?

Answer 32

Yes.

Question 33

How are insoluble salts made?

Answer 33

Precipitation reactions.

Question 34

What is electrolysis?

Answer 34

The breaking down of a substance using electricity.

Question 35

What is oxidation?`

Answer 35

The loss of electrons in a reaction.

Question 36

What is a reduction reaction?

Answer 36

Gaining electrons in a reaction.

Question 37

How does electrolysis work?

Answer 37

By passing an electric current through a electrolyte, causing it to decompose.

Question 38

What is an electrolyte?

Answer 38

A molten or dissolved ionic compound.

Question 39

What makes up an electrochemical cell?

Answer 39

A cathode, anode, d.c power supply and an electrolyte.

Question 40

In electrolysis, what happens to the ions?

Answer 40

They head to either electrode depending on charge.

Question 41

In electrolysis, where do positive ions head?

Answer 41

Towards the cathode.

Question 42

In electrolysis, where do negative ions head?

Answer 42

Towards the anode.

Question 43

In electrolysis of an aqueous solution, how could hydrogen gas form?

Answer 43

Provided hydrogen ions are present and the metal is more reactive than hydrogen then hydrogen gas begins to form at the cathode.

Question 44

In electrolysis of an aqueous solution, how could oxygen be formed?

Answer 44

Provided no halide ions are present then oxygen will form at the anode.