2 Foundations In Chemistry- Acids 4.1-4.3

Question 1

Acids and bases

Answer 1

are on the opposite ends of the pH scale. They combine to form water, which is neutral.

Question 2

Acids

Answer 2

Acids are substances that form hydrogen (H+) ions when they dissolve in water (aqueous solutions).
Acids are proton donors.

neutralise bases to form salt and water. An acid can be strong or weak - this will affect its dissociation.

Question 3

Bases

Answer 3

Alkalis are substances that form hydroxide (OH-) ions when they dissolve in water (aqueous solutions).
Bases can neutralise acids.
An alkali is a type of base. An alkali is a base that’s soluble in water.
Bases are proton acceptors.

Bases are metallic oxides or hydroxides (or ammonia) that neutralise acids to form salt and water.

Question 4

Sulphuric acid

Answer 4

H2SO4

Question 5

Nitric acid

Answer 5

HNO3

Question 6

Ethanoic acid

Answer 6

CH3COOH

Question 7

Sodium hydroxide

Answer 7

NaOH

Question 8

Potassium hydroxide

Answer 8

KOH

Question 9

Ammonia

Answer 9

NH3

Question 10

Water dissociation

Answer 10

Water dissociates to give a proton and a hydroxide.

H2O ⇋ H+ + OH−

Question 11

Weak base

Answer 11

Weak bases don’t fully ionise in aqueous solutions.
Ammonia solution is an example of a weak base.
It exists mainly as NH3 molecules. Only a few of these react with water molecules to form ions.
NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq).

Question 12

Strong base

Answer 12

Aqueous sodium hydroxide and potassium hydroxide are examples of strong bases.
Strong bases fully ionise in aqueous solutions.
NaOH(aq) → Na+(aq) + OH-.
KOH(aq) → K+(aq) + OH-.

Question 13

Weak acid

Answer 13

Weak acids don’t fully ionise in aqueous solutions.
Ethanoic acid is an example of a weak acid.
Ethanoic acid exists mainly as CH3COOH molecules. Only a few of these react with water molecules to form ions.
CH3COOH(aq) + H2O(l) ⇌ H3O+(aq) + CH3COO-(aq)

Question 14

Strong acid

Answer 14

Aqueous HCl, HNO3 and H2SO4 are examples of strong acids.
Strong acids fully ionise in aqueous solutions.
HCl(aq) → H+(aq) + Cl-.
HNO3(aq) → H+(aq) + NO3-.

Question 15

Acid + metal oxide

Answer 15

Produces salt + water

Question 16

Acid + metal carbonate

Answer 16

Produces salt + water + carbon dioxide

Question 17

Titration technique

Answer 17

In a titration, you want to calculate the concentration of an acid or base by reacting it with a known amount of base or acid. To do this:
Add a measured amount of one to the other.
Use a balanced equation to calculate the concentrations.

Question 18

Titrations- accuracy

Answer 18

In a titration, you want to make sure you have accurate results.
Accurate results are achieved by repeating your titration until you get concordant results.
Concordant results are values that are within 0.1 cm3 of each other.

Question 19

Phenolphthalein and methyl orange indicators

Answer 19

Phenolphthalein changes from colourless to pink from pH 8.3 to pH 10.
Methyl orange changes colour from red to yellow between pH 3.1 and pH 4.4.

Question 20

Oxidising agents

Answer 20

An oxidising agent oxidises something else.
It takes electrons from another compound.
This means it gains electrons itself.
So an oxidising agent is itself reduced.

Question 21

Reducing agents

Answer 21

A reducing agent reduces something else.
It gives electrons to another compound.
This means it loses electrons itself.
So a reducing agent itself is oxidised.

Question 22

Oxidation states

Answer 22

An oxidation state shows how many electrons an atom has gained or lost.
The concept of oxidation state is related to electronegativity.
Electronegativities can be used to work out oxidation states.

Question 23

Ionic half equations

Answer 23

An ionic half equation shows either reduction or oxidation.
An example is: O2 + 4e- → 2O2-
This is the ionic half equation for the reduction of O2 to 2O2-
If you have ionic half equations for both a reduction process and an oxidation process, you can add the two to generate a full balanced equation.