Module 2: Chapter 4 (Acids and redox)

Question 1

What are the formula of 4 common acids?

Answer 1

hydrochloric acid -> HCl
sulphuric acid -> H2SO4
nitric acid -> HNO3
ethanoic acid -> CH3COOH

Question 2

What are the formulae of 3 common alkalis?

Answer 2

sodium hydroxide -> NaOH
potassium hydroxide -> KOH
ammonia -> NH3

Question 3

What are acids?

Answer 3

when dissolved in water an acid releases H+ ions into the solution (dissociation)

Question 4

What is the difference between a strong acid and a weak acid?

Answer 4

• a strong acid completely dissociates in water (HCl, HNO3, H2SO4)
• for a weak acid dissociation is incomplete, written as an equilibrium (carboxylic acid)

Question 5

What is the ethanoate ion?

Answer 5

CH3COO-

Question 6

What is a base?

Answer 6

• metal oxides, metal hydroxides, metal carbonates and ammonia are all classified as bases
• a base neutralises an acid to form a salt

Question 7

What is an alkali?

Answer 7

an alkali is a base that dissolves in water releasing hydroxide ions

Question 8

State the 4 general reactions involving acids

Answer 8

1. acid + alkali -> salt + water
2. acid + metal oxide -> salt + water
3. acid + carbonate -> salt + water + CO2
4. acid + ammonia -> ammonium salt

Question 9

How do you prepare a standard solution in an acid-based titration?

Answer 9

1. solid is weighed accurately
2. solid dissolves in a beaker with distilled water, less than what is needed to fill flask
3. solution is transferred to a volumetric flask (traces are rinsed with distilled water into the flask)
4. flask filled to the graduation line by adding distilled water a drop at a time until the bottom of the meniscus lines up exactly at eye level (if over solution must be prepared again)
5. flask slowly inverted many times to mix solution thoroughly (if not done titration results will be inconsistent)

Question 10

What are the 3 steps for titration calculations?

Answer 10

1. work out the amount, in mol, of the solute in the solution for which you know both the concentration and volume
2. use the equation to work out , in mol, of the solute in the other solution
3. work out the unknown information about eh solute in the other solution

Question 11

Oxidation Rules: simple ions

Answer 11

oxidation number is just the charge on the ion

Question 12

Oxidation Rules: elements

Answer 12

oxidation number for elements not in a compound is zero

Question 13

Oxidation Rules: fluorine

Answer 13

ALWAYS -1

Question 14

Oxidation Rules: oxygen

Answer 14

-2, unless bonded to F or in a peroxide like H2O2

Question 15

Oxidation Rules: chlorine

Answer 15

-1, unless bonded to F or O

Question 16

Oxidation Rules: bromine

Answer 16

-1, unless bonded to F, O or Cl

Question 17

Oxidation Rules: iodine

Answer 17

-1, unless bonded to F, O, Cl or Br

Question 18

Oxidation Rules: hydrogen

Answer 18

+1, unless it’s present as a hydride ion

Question 19

Oxidation Rules: group 1 or group 2 metals

Answer 19

group 1 or 2 metals will always be present ions in their compounds so will be +1 and +2

Question 20

Oxidation Rules: compounds

Answer 20

oxidation number of each atom must add up to the charge of the compound

Question 21

Oxidation Rules: sign

Answer 21

sign is put BEFORE the oxidation number, unlike charges

Question 22

What is meant by oxidation?

Answer 22

oxidation is the loss of electrons or increase in oxidation number

Question 23

What is meant by reduction?

Answer 23

reduction is gain of electrons or decrease in oxidation number

Question 24

What is the oxidising agent?

Answer 24

takes electrons from the species being oxidised

- therefore contains the species that is reduced

Question 25

What is the reducing agent?

Answer 25

gives electrons to the species being reduced

- contains the species that is oxidised