4 Acids and redox

Question 1

What element do all acids contain? (1 mark)

Answer 1

Hydrogen

Question 2

What does an acid release when dissolved in water? (1 mark)

Answer 2

H+ ions

Question 3

What is a strong acid? (2 marks)

Answer 3

A strong acid releases all its hydrogen atoms into solution as H+ ions
and completely dissociates in aqueous solution.

Question 4

What is a weak acid? (2 marks)

Answer 4

A weak acid only releases a very small proportion of its available hydrogen atoms into solution as H+ ions.
A weak acid only partially dissociates.

Question 5

Define the term ‘base’. (1 mark)

Answer 5

A base is a substance which readily accepts H+ ions.

Question 6

What is an alkali? (2 marks)

Answer 6

An alkali is a base that dissolves in water
releasing OH- ions into the solution.

Question 7

What does an alkali release when dissolved in water? (1 mark)

Answer 7

OH- ions

Question 8

Describe what happens when an acid is neutralised. (2 marks)

Answer 8

The H+ ions from acid react with OH- ions from base to form a salt and neutral water.

Question 9

What is formed when an acid reacts with a metal hydroxide? (2 marks)

Answer 9

Water and a salt

Question 10

What is formed when an acid reacts with a metal oxide? (2 marks)

Answer 10

Water and a salt

Question 11

What are formed when an acid and alkali react? (2 marks)

Answer 11

Water and a salt

Question 12

What are formed when an acid and metal carbonate react? (2 marks)

Answer 12

Water, carbon dioxide, and a salt

Question 13

Explain the statement ‘Sulphuric acid is a strong acid, but this is true only for one of the two hydrogen atoms. (3 marks)

Answer 13

When sulphuric acid is mixed with water each H2SO4 molecule dissociates, releasing just one of its two hydrogen atoms as an H+ ion.
This means HSO4 - ions are formed, which behave as a weak acid.

Question 14

Finish the sentence:
A burette reading is recorded to the nearest…. (1 mark)

Answer 14

Half division

Question 15

What is a concordant result, in titration, and what are they used for? (2 marks)

Answer 15

Titres within 0.10cm3 of each other.
They are used to calculate the mean titre.

Question 16

What is the oxidation number of an element? (1 mark)

Answer 16

0

Question 17

Where is the sign placed for an oxidation number? (1 mark)

Answer 17

BEFORE the number

Question 18

What is the oxidation number of hydrogen in metal hydroxides? (1 mark)

Answer 18

-1
e.g. NaH or CaH2

Question 19

What is the oxidation number of oxygen in peroxides? (1 mark)

Answer 19

-1
e.g H2O2

Question 20

What is the oxidation number of oxygen when bonded to fluorine? (1 mark)

Answer 20

+2
e.g. F2O

Question 21

What is a redox reaction? (1 mark)

Answer 21

Redox reactions involve reduction and oxidation.

Question 22

What is oxidation in terms of electrons? (1 mark)

Answer 22

The loss of electrons.

Question 23

What is reduction, in terms of electrons? (1 mark)

Answer 23

The gain of electrons.

Question 24

What is oxidation, in terms of oxygen? (1 mark)

Answer 24

Gain of oxygen.

Question 25

What is reduction, in terms of oxygen? (1 mark)

Answer 25

Loss of oxygen.

Question 26

What is oxidation, in terms of oxidation number? (1 mark)

Answer 26

Increase in oxidation number.

Question 27

What is reduction, in terms of oxidation number? (1 mark)

Answer 27

Decrease in oxidation number.

Question 28

What is the significance of oxidation number in equations? (1 mark)

Answer 28

The changes in oxidation number balance out in an equation.