Chapter 4 - Acids and redox

Question 1

What is an acid?

Answer 1

A substance which in an aqueous solution will release H+ ions

Question 2

Why are acids referred to as proton donors?

Answer 2

They release a proton in the form of a H+ ion to ‘donate’ to a base

Question 3

What is a strong acid?

Answer 3

A substance where every molecule of the acid is split up into H+ and a negative ion in aqueous solution. None of it exists as the whole molecule (100% ionised), it completely disassociates

Question 4

What are the four main strong acids?

Answer 4

Hydrochloric, sulfuric, nitric, phopshoric

Question 5

What is the equation for a strong acid in solution?

Answer 5

HA → H+ + A-

Question 6

What is the equation for hydrochloric acid being ionised in solution?

Answer 6

HCl → H+ + Cl-

Question 7

What is the equation for sulfuric acid being ionised in solution?

Answer 7

H2SO4 → H+ + HSO4-

Question 8

What is the equation for nitric acid being ionised in solution?

Answer 8

HNO3 → H+ + NO3-

Question 9

What is the equation for phosphoric acid being ionised in solution?

Answer 9

H3PO4 → H+ + H2PO4-

Question 10

What is a weak acid?

Answer 10

A substance where only some of the acid molecules are split up into H+ and a negative ion in aqueous solution. Some of it still exists as the whole molecule, it partially disassociates

Question 11

What is the equation for a weak acid being ionised in solution?

Answer 11

AH ⇌ H+ + A-

Question 12

What are some examples of weak acids?

Answer 12

Carboxylic acids and most organic acids

Question 13

What is a base?

Answer 13

A substance that neutralises an acid to form a salt

Question 14

What is an alkali?

Answer 14

A base that dissolves in water to release hydroxide (OH-) ions into the solution

Question 15

What is the word equation for a neutralisation reaction between an acid and an alkali?

Answer 15

acid + alkali → salt + water

Question 16

What is the word equation for the reaction between an acid and metal oxide or hydroxide?

Answer 16

acid + metal oxide/hydroxide → salt + water

Question 17

What is the word equation for the reaction between an acid and a metal carbonate?

Answer 17

acid + metal carbonate → salt + water + carbon dioxide

Question 18

What is the ionic equation for a neutralisation reaction?

Answer 18

H+ + OH- → H2O

Question 19

What is a titration?

Answer 19

A technique used to accurately measure the volume of one solution that reacts exactly with another solution

Question 20

What can titrations be used for?

Answer 20

• finding the concentration of a solution
• identification of unknown chemicals
• finding the purity of a substance

Question 21

What is a standard solution?

Answer 21

A solution of known concentration

Question 22

When do you stop the repeats of a titration?

Answer 22

When the results are concordant (within 0.10 cm³ of each other)

Question 23

What is an oxidation number?

Answer 23

The total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom

Question 24

What is the oxidation number for elements?

Answer 24

It is always zero

Question 25

What are the rules for working out oxidation numbers?

Answer 25

• on simple ions, oxidation state = charge on ion
• in elements, oxidation state is always 0
• sum of oxidation numbers = total/overall charge
• in molecules, the more electronegative element is assumed to be the negative ion
• H is nearly always +1 and oxygen -2

Question 26

What is the oxidation number of the Group 1 metals always?

Answer 26

+1

Question 27

What is the oxidation number of the Group 2 metals always?

Answer 27

+2

Question 28

What is usually the oxidation number of O, and what are the exceptions?

Answer 28

usually -2, except in peroxides and F2O

Question 29

What is usually the oxidation number of hydrogen, and what are the exceptions to this?

Answer 29

usually +1, except in metal hydrides where it is -1

Question 30

What is the oxidation number of fluorine always?

Answer 30

-1

Question 31

What is the oxidation number of chlorine usually, and what are the exceptions to this?

Answer 31

usually -1, except in compounds with O or F

Question 32

What is oxidation?

Answer 32

Oxidation can be defined as:

• the loss of electrons
• the addition of oxygen
• an increase in oxidation number

Question 33

What is reduction?

Answer 33

Reduction can be defined as:

• the gain of electrons
• the removal of oxygen
• a decrease in oxidation number

Question 34

What are redox reactions?

Answer 34

Redox reactions are ones involving both reduction and oxidation

Question 35

What is a salt?

Answer 35

A substance where the H+ ion in the acid has been replaced by a metal ion (formed from reaction between acid and base)