Topic 4 - Chemical Changes

Question 1

What does the pH scale measure?

Answer 1

How acidic or alkali something is

Question 2

What is the pH of an acid

Answer 2

0-6

Question 3

What is the pH of an alkali?

Answer 3

8-14

Question 4

What does an acid form in water?

Answer 4

H+ ions

Question 5

What does an alkali produce in water?

Answer 5

OH- ions

Question 6

What is the name of the reaction between an acid and a base?

Answer 6

Neutralisation

Question 7

What is the word and symbol equation for neutralisation?

Answer 7

Acid + Base -> Salt + Water

H+ + OH- -> H20

Question 8

When adding strong and weak acids to water, what is the difference?

Answer 8

Strong acid ionise completely making lots of H+ ions but Weak Acids don’t fully ionise making less H+ ions

Question 9

Why is the pH different in strong and weak acids?

Answer 9

Strong acids have more H+ ions

Question 10

What concentration does the pH scale measure?

Answer 10

The concentration of H+ ions

Question 11

What is the relationship tween an increased of H+ ions and a decrease in a pH by 1?

Answer 11

For every decrease of 1 in the scale the conc of H+ ions increases by a factor of 1

E.g. an acid of pH 4 has 10 times more H+ ions then an acid of pH5

Question 12

Can metal oxides and metal hydroxides dissolve in water?

Answer 12

Yes. Some metal oxides and metal hydroxides dissolve in water

Question 13

What is the word equation for a metal oxide/hydroxide being added to acid?

Answer 13

Acid + metal oxide/metal hydroxide -> salt + water

Question 14

Are metal oxides and hydroxides acid or alkali and how do we know?

Answer 14

They are alkali and we know because the form a salt and water when dropped in acid. The neutralise

Question 15

What is the word equation for a metal carbonate dropped into acid?

Answer 15

Acid + metal carbonate -> Salt + Water + Carbon Dioxide

Question 16

What does oxidation and reduction mean?

Answer 16

Oxidisation - a gain in oxygen or loss of electrons
Reduction - a loss in oxygen or gain of electrons

Question 17

What is a redox reaction?

Answer 17

A reaction where reduction and oxidisation is happening simultaneously

Question 18

What is a displacement reaction?

Answer 18

A more reactive metal will displace a less reactive metal from its compound. They are redox reactions

Question 19

Give a word and symbol equation as an example of a displacement reaction

Answer 19

Iron + copper sulphate -> copper + iron sulphate
Fe + CuSo4 -> FeSo4 + Cu

Question 20

What is an ionic equation?

Answer 20

An ionic equation is an equation where only the particles that react and the products are shown.

Question 21

What is electrolysis?

Answer 21

The process of splitting up an ionic compound with electricity

Question 22

What substances can be electrolysed?

Answer 22

Electrolysis works with both molten ionic solids and aqueous solutions

Question 23

Why can’t an ionic solid be electrolysed?

Answer 23

It’s ions are not free to flow

Question 24

When electrolysing molten solids, what forms at the anode?

Answer 24

Non metal ions are oxidised (lose electrons)

Question 25

When electrolysing molten solids, what forms at the cathode?

Answer 25

Positive metal ions - they are reduced - gain electrons

Question 26

Which way do ions move in electrolysis?

Answer 26

Positive ions move towards the cathode and gain electrons. Negative ions move toward the anode and lose electrons

Question 27

What electrode is negative and what one is positive?

Answer 27

The cathode is negative and the anode in positive

Question 28

When electrolysing aqueous solutions, what forms on the cathode?

Answer 28

If H+ ions and metal ions are present, hydrogen gas will be produced if the metal ions form a metal more reactive than hydrogen. If the metal is less reactive than hydrogen the metal will be produced instead

Question 29

When electrolysing aqueous solutions, what forms around the anode?

Answer 29

If OH- ions and halide ions are present the halide will be produced, if no halide is present then OH- ions are discharged and oxygen is formed.

Question 30

What are half equations?

Answer 30

Half equations are used to show the reactions at both electrodes. Half equations need balanced electrons on both the negative and positive equation.

Question 31

What is the point of a titration?

Answer 31

A titration is used to find out exactly how much acid is needed to neutralise a quantity of alkali

Question 32

What indicator is most commonly used for titration?

Answer 32

Phenolphthalein

Question 33

What colours is phenolphthalein when acid and alkali?

Answer 33

Acid - clear Alkali - pink

Question 34

What colours is litmus when acid and alkali?

Answer 34

Acid - red Alkali - blue/purple

Question 35

What colour is methyl orange when acid or alkali?

Answer 35

Acid - red Alkali - yellow

Question 36

What is the order of the reactivity series?

Answer 36

Potassium, sodium, lithium, calcium, magnesium, carbon, zinc, iron, hydrogen, copper

Question 37

What are the two ways of extracting metals from metal oxides?

Answer 37

More reactive than carbon - electrolysis Less reactive than carbon - reduction my carbon

Question 38

What are some metals more reactive than others?

Answer 38

It depends on the metals tendency to form positive ions

Question 39

What is the difference between a sting and weak acid?

Answer 39

A strong acid is completely ionised in aqueous solutions whereas a weak acid is only partially ionised