Hard water

Question 1

Hard water

Answer 1

Caused by Mg and Ca (2+)
Doesn’t easily lather with soap

Question 2

Temp hardness

Answer 2

Removed by boiling
Caused by carbonates and hydrogen-carbonates
Eg, Ca(HCO3) Mg(HCO3) , CaCo3 , MgCO3

Question 3

Permanent hardness

Answer 3

Cannot be removed by boiling
Caused by sulphites and chlorides
MgCl2 CaCl2 MgSO4 CaSO4

Question 4

Causes of temporary water hardness

Answer 4

Water mixes with Co2 to form a carbonic acid
H20+CO2—>H2CO3

Carbonic acid mixes with limestone and forms calcium hydrogen carbonate
.
H2CO3+CaCO3—>Ca(HCO3)2

Calcium hydrogen carbonate dissociates to form hard water
Ca(HCo3)2—>Ca2+ + 2HCo3

Question 5

Limescale

Answer 5

When temp hard water is boiled down it forms a white precipitate because limestone (CaCo3) is insoluble

Damages kettles and hot pipes

Question 6

Removing permanent hardness
1.Distillation

Answer 6

Evaporating off water leaves salts behind
When water is condensed it has no more salts and becomes ‘soft’

Question 7

Removing permanent hardness
2. Washing soda

Answer 7

Hydrated sodium carbonate
(Na2Co3.10H2O) removes water hardness and allows it to late her with soap. Reacted with calcium ions

Ca2+Co3—>CaCo3

Question 8

Removing permanent hardness
3. Ion Exchange

Answer 8

Cation Exchange swaps with ions that cause water hardness (Ca2+ Mg2+)

Ca2+ + 2RNa—>R2Ca+2Na+

Question 9

Deionised water

Answer 9

Involves both cation exchange and anion exchange

The hydrogen ions and hydroxide ions combine to give water

H+ + Co- —>H2O

Question 10

Cation exchange

Answer 10

All metal ions are replaced by hydrogen ions

M+ + HR —> MR + H+

Question 11

Anion exchange

Answer 11

All anions in the water are replaced by hydroxide ions
A- + ROH—> RA + OH-

Question 12

Deionised v Distilled water

Answer 12

Deionised
-no ions
-Has dissolved gases and organic material

Distilled
-no ions
-no dissolved gases and organic materials

Question 13

Heavy metal pollution

Answer 13

Dispositive ions of heavy metals
Lead , Mercury and Cadmium can get into water ways by industrial effluent and the into drinking water.

Theses metals are poisonous , lead can be removed by precipitation.

Question 14

Calculate the BOD

Answer 14

Sample is divided into 2
Concentration of dissolved oxygen in one is measured.
Other gets left in the dark.. the concentration of dissolved oxygen is measured after
BOD is subtracted , taking into account any factors.