Water and Solutions (Including Water Hardness)

The purification of Brackish and Sea Water, including diagram

Brackish and Sea Water can be purified by Reverse Osmosis. Normal osmosis occurs when water moves from a dilute solution to a concentrated solution. In this case it is the opposite, hence Reverse Osmosis

Substance	Solubility (including exceptions)
Group 1 and Ammonium Salts
Nitrates
Chlorides
Sulfates
Carbonates
Hydroxides
Hydrogen Carbonates

Substance	Solubility (including exceptions)
Group 1 and Ammonium Salts	Soluble
Nitrates	Soluble
Chlorides	Soluble except Silver and Lead Chlorides
Sulfates	Soluble except Lead, Barium, and Calcium Sulfates
Carbonates	Insoluble except Group 1 and Ammonium Carbonates
Hydroxides	Insoluble except Group 1 and Ammonium Hydroxides
Hydrogen Carbonates	Soluble

Answer the following questions by referring to the solubility curve

1. How much copper (II) sulfate will dissolve in 100g of water at 55℃?

2. What would you see when a saturated solution of copper (II) sulfate is heated from 80℃ to 20℃?

3. How much copper (II) sulfate will dissolve in 20g of water at 30℃?

1. 37.5g

2. 30g of CuSO₄ crystals will appear

3. 4.8g

Efflorescence

The loss of water of crystallisation from a hydrated salt to the atmosphere on exposure to air

Deliquescence

The ability of a substance to absorb water vapour from the air and dissolve in it

Hygroscopic

The ability of a substance to absorb water vapour from the air but doesn’t dissolve in it

Testing for the presence of water

Check whether the liquid turns anhydrous copper sulfate (white powder) into hydrated copper sulfate (blue crystals)

Testing for the purity of water

Check whether the melting point of the water is 0℃ and the boiling point is 100℃

Element	(Reacts with cold water / reacts with steam / unable to react with water)	Products of the reaction with water
Potassium
Sodium
Calcium
Magnesium
Aluminium
Zinc
Iron
Lead
Copper
Silver

Element	(Reacts with cold water / reacts with steam / unable to react with water)	Products of the reaction with water
Potassium	Reacts with cold water	Potassium Hydroxide and Hydrogen
Sodium	Reacts with cold water	Sodium Hydroxide and Hydrogen
Calcium	Reacts with cold water	Calcium Hydroxide and Hydrogen
Magnesium	Reacts with steam	Magnesium Oxide and Hydrogen
Aluminium	Reacts with steam	Aluminium Oxide and Hydrogen
Zinc	Reacts with steam	Zinc Oxide and Hydrogen
Iron	Reacts with steam	Iron Oxide and Hydrogen
Lead	Unable to react with water	/
Copper	Unable to react with water	/
Silver	Unable to react with water	/

The chemical and word equation for the reaction between Chlorine and Water

Cl₂ + H₂O → HOCl + HCl

Chlorine + Water → Hypochlorous Acid + Hydrochloric Acid

The test for chlorine

Add a damp blue litmus paper. Since the water on the paper will react with the chlorine, it will form hydrochloric acid and hypochlorous acid

The hydrochloric acid will first turn the litmus paper from blue to red since it’s an acid

The hypochlorous acid will then turn the litmus paper from red to white (bleaching it) since it’s a bleach

Hard water

Hard water is water which doesn’t easily lather with soap. Hard water is formed when solid impurities of Calcium or Magnesium dissolve in it

The difference between hard and soft water

Hard water forms scum (a white precipitate) when soap is added

Soft water forms lather (a frothy white solid) when soap is added

The difference between permanent and temporary water hardness

Permanently hard water cannot be removed by boiling whilst temporarily hard water can

The 2 compounds that form temporary hardness in water

Calcium Sulfate and Magnesium Sulfate

The 2 compounds that form temporary hardness in water

Calcium Hydrogen Carbonate and Magnesium Hydrogen Carbonate

The substance which converts neutral water into acidified water, causing it to dissolve calcium carbonate

Carbon Dioxide

The chemical equation of the dissolving of calcium carbonate by acid rain

CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂

or

CaCO₃ + H₂CO₃ → Ca(HCO₃)₂

The reason why temporary hard water can be removed by boiling

Since Calcium Hydrogen Carbonate (one of the compounds which cause temporary hardness) can decompose by heat to form Calcium Carbonate, water and carbon dioxide

The chemical formula of soap

NaSt (Sodium Stearate)

The chemical formulae of scum

CaSt₂ (Calcium Stearate) or MgSt₂ (Magnesium Stearate)

The reactions between the 2 types of temporary hard water and soap

Ca(HCO₃)₂ + NaSt → NaHCO₃ + CaSt₂

Mg(HCO₃)₂ + NaSt → NaHCO₃ + MgSt₂

The reactions between the 2 types of permanent hard water and soap

CaSO₄ + NaSt → Na₂SO₄ + CaSt₂

MgSO₄ + NaSt → Na₂SO₄ + MgSt₂

The 3 methods of water hardness removal

1. Boiling (temporary hardness only)

2. Adding washing soda, Na₂CO₃

3. Distillation