8. Acids, bases and salts

Question 1

Describe the characteristic properties of acids in terms of their reactions with:

(a) metals
(b) bases
(c) carbonates
(d) insoluble base
(e) ammonia

(f) base with ammonium

Answer 1

(a) metal (above H2) + acid → salt + hydrogen

(b) acid + base → salt + water (neutrailisation)

(c) metal carbonate + acid → salt+ CO2 + water

(d) acid + metal oxide → salt + water
for unreactive metals- Pb, Cu, Ag, Au

(e) ammonia + acid → salt

(f) base + ammonium → salt + water + ammonia

Question 2

Colour of acid and alkali in

(a) litmus
(b) thymolphthalein
(c) methyl orange

Answer 2

(a) litmus- red- blue
(b) thymolphthalein- colourless- blue
(c) methyl orange- pink- yellow

Question 3

Difference between bases and alkali

Answer 3

bases are oxides or hydroxides of
metals and that alkalis are soluble bases

Question 4

Define acids and bases

Answer 4

proton donors- aqueous solutions of acids contain H+ ions

proton acceptors- aqueous solutions of alkalis contain OH– ions

Question 5

Define a strong acid and a weak acid

Answer 5

an acid that is completely dissociated in aqueous solution.

an acid that is partially dissociated in aqueous solution

hydrochloric acid is a strong acid,
HCl(aq) → H+ (aq) + Cl– (aq)

ethanoic acid is a weak acid,
CH3COOH(aq) ⇌ H+ (aq) + CH3COO– (aq)

Question 6

Describe the neutralisation reaction

How to compare hydrogen ion concentration, neutrality, relative acidity and relative alkalinity in terms of colour and pH using universal indicator paper

Answer 6

H+ (aq) + OH– (aq) → H2O(l)

the higher the concentration of H+ ions, lower the pH and stronger the acid

the higher the concentration of OH- ions, higher the pH and stronger the alkali

red to purple. neutral- green

Question 7

OXIDES!

Answer 7

amphoteric oxides- oxides that react with acids and with bases to produce a salt and water- Al2O3 and ZnO

metal oxide- basic- react with acids- CuO and CaO
non-metal oxide- acidic- react with base- SO2 and CO2

neutral oxides- carbon monoxide, nitrous oxides

Question 8

soluble salt

Answer 8

metal/ metal carbonate-

1. add metal in excess ( till effervescence stops)
   2.filter, evaporate filtrate till crystallisation point.
2. wash and dry.

insoluble base- heat for faster ROR as unreactive

soluble base- titration and then heat till crystallisation, wash, dry.

Question 9

insoluble salt preparation- precipitation

Answer 9

Dissolve lead(II) nitrate and potassium sulfate in water and mix together using a stirring rod in a beaker

Filter to remove precipitate from mixture

Wash precipitate with water to remove traces of potassium nitrate solution

dry using a filter paper

Question 10

Solubility rules

Answer 10

(a) sodium, potassium and ammonium salts are soluble

(b) nitrates are soluble

(c) chlorides are soluble, except lead and silver

(d) sulfates are soluble, except barium, calcium and lead

(e) carbonates are insoluble, except sodium, potassium and ammonium

(f) hydroxides are insoluble, except sodium, potassium, ammonium and
calcium (partially)

Question 11

Define a hydrated substance, an anhydrous substance and water of crystallisation

Answer 11

a substance that is chemically combined with water

a substance containing no water

the water molecules present in hydrated crystals, including CuSO4.5H2O and CoCl 2.6H2O