5-Acids And Bases

Question 1

The pH scale

Answer 1

Stretches from below 0 to below 14
Starting with strong acids from 1 getting weaker till 6 then neutral at 7, weak alkalis starting at 8 getting stronger till 14

Question 2

What is pH?

Answer 2

A measure of the hydrogen (h+(aq)) ion concentration of a solution

Question 3

What is the equation for the dissociation of water molecules?

Answer 3

H O (l) reversible sign H+ (aq) + OH- (aq)
2

Question 4

Explain acid solutions

Answer 4

They contain a greater concentration of H+(aq) ions than OH-(aq) ions so have a pH below 7
They all contain the hydrogen ion

Question 5

Explain alkali solutions

Answer 5

They contain a greater concentration of OH- (aq) ions than H+ (aq) ions so have a pH above 7
They all contain the hydroxide ion

Question 6

Explain neutral solutions

Answer 6

Contain an equal concentration of hydrogen and hydroxide ions so have a pH of 7

Question 7

Explain the conductivity of acids and alkalis

Answer 7

They are good conductors of electricity because they contain many oppositely charged ions that are free to move in solution

Question 8

Explain the conductivity of water

Answer 8

Water is a poor conductor of electricity because of the prescience of a small number of ions

Question 9

Explain dilution

Answer 9

Reducing the concentration of a substance (usually done by adding water)
Tracked by using a chemical indicator
Concentration of ions will always decrease when the solution is diluted

Question 10

What is indicator?

Answer 10

Chemicals which change colour according to pH

Question 11

Explain the dilution of acids

Answer 11

When an acid is diluted, the pH will increase towards 7 because the concentration of hydroxide (H+) ions is reduced
Solution becomes less acidic as water is added

Question 12

Explain the dilution of alkalis

Answer 12

When an alkali is diluted, the pH will decrease towards 7 because the concentration of hydroxide (OH-) ions is reduced
Solution becomes less alkaline as water is added

Question 13

Formulae of acids and ions present

Answer 13

Hydrochloric acid HCl(aq) H+ (aq) + Cl- (aq)
Nitric acid HNO3 (aq) H+(aq) +NO3-(aq)
Sulphuric acid H2SO4(aq) 2H+(aq)+SO4 2-(aq)
Or use SVSDF if formulae forgotten

Question 14

Forming acids and alkalis

Answer 14

Acids and alkalis can be formed by dissolving oxides in water
Non-metal oxide (soluble) + water —) acid
Metal oxide (or hydroxide) + water —) alkali solution

Question 15

Bases

Answer 15

Substance that neutralises an acid
Bases that dissolve in water form alkaline solutions
Metal oxides, metal hydroxides, metal carbonates and ammonia are all bases

Question 16

Neutralisation reactions

Answer 16

One in which a base reacts with an acid to form water
Salt is also formed
Acid + base —) salt + water

Question 17

Naming salts

Answer 17

Base name= start salt name
Potassium hydroxide= potassium
Sodium hydroxide= sodium
Magnesium hydroxide= magnesium

Acid name= salt name ending
Hydrochloric acid= chloride
Sulphuric acid= sulphate
Nitric acid= nitrate

Question 18

Neutralisation of an acid

Answer 18

Adding an alkali to an acid will increase the pH of the solution towards 7

Question 19

Neutralisation of an alkali

Answer 19

Adding an acid t an alkali will decrease the pH of the solution towards 7

Question 20

Neutralisation reactions-different bases

Answer 20

All alkalis are bases but not all bases are alkalis
Metal oxide+acid —) salt+water
Metal hydroxide+acid —) salt+water
Metal carbonate+acid —) salt+water+carbon dioxide