Water treatment and a study of hard water is used to amplify the chemistry of solutions. The use of detergents and non-aqueous solvents for cleaning leads to a general discussion of water pollution.

(Note that calculations of concentration are not included at this stage)

If soap lathers easily, it means the water contains very little CALCIUM and MAGNESIUM compounds. It is SOFT WATER.

A GREYISH SCUM and hardly any lather shows that MORE CALCIUM and MAGNESIUM is present. The water is called HARD WATER.

SCUM-- Calcium and Magnesium compounds react with SOAP to give an INSOLUBLE product.

FORMULA: Calcium Suphate + Sodium Stearate (soap) -->  Calcium Stearate (scum) + Sodium Sulphate

HARD WATER contains lots of CALCIUM HYDROGENCARBONATE. On Heating, the compound breaks down to form CALCIUM CARBONATE (insoluble) and releases HYDROGEN gas.  When Hydrogencarbonate is removed, water becomes SOFT WATER.

CALCIUM HYDROGENCARBONATE= Ca(HCO3)2

Since CALCIUM CARBONATE can be removed by BOILING, the HARDNESS caused by it is called TEMPORARY HARDNESS.

Hardness caused by other compounds is called PERMANENT HARDNESS. This is because BOILING will not remove the compound causing the water to become Hard Water. Even after boiling water with Permanent Hardness, SCUM will still form with SOAP.

SOLUTION-- a HOMOGENOUS mixture. 2 or more Substances combined. A SOLUTE is DISSOLVED in another substance, known as the SOLVENT.

(SOLUTE--  is dissolved.

SOLVENT--  is the DISSOLVER,  or DISSOLVING  substance.)

Some substances are more soluble in water than others. A substance that is completely soluble in water (100% dissolved) is called MISCIBLE. 

EXOTHERMIC REACTION--  gives out HEAT  (therm means 'heat' in Greek) when reacting. Heat is transferred to the surroundings.

It can be summarized as: Reactants --> Products + HEAT ENERGY

EXAMPLES OF EXOTHERMIC REACTIONS:

• neutralization of an ACID by an ALKALI
• COMBUSTION of Fuels. If they didn't give out Heat energy, they'd be no good as fuels.
• RESPIRATION in our body's CELLS. It provides ENERGY to keep our Heart and Lungs working, and for warmth and movement.

UNIT for ENERGY:  the  symbol  J for joules.

1 kilojoule (kJ) = 1,000 J

duh.

When ACIDS react with ALKALIS, the TEMPERATURE of the solution INCREASES. 

ANTACID--  something that NEUTRALIZES acids. duh. 

Acids can be neutralized by ALKALIS, however, we usually avoid CONCENTRATED and STRONG alkalis in antacid tablets, as they are corrosive. And they can kill you.

In ANTACID tablets, we usually add other things that wont kill us. Some of these are listed below.

ACID + METAL HYDROXIDE    --> METAL SALT  +  WATER

ACID + METAL                        --> METAL SALT  + HYDROGEN

ACID + METAL CARBONATE    --> METAL SALT +  WATER         + CARBON DIOXIDE

ACID + METAL OXIDE             --> METAL SALT  +  WATER Edit tags

You can test for chloride ions (in a solution) by acidifying the solution with dilute nitric acid then add aqueous silver nitrate. this should produce a white precipitate.

You can test sulphate ions (in a solution) by acidifying the solution with and then adding aqueous barium nitrate. this should give a white precipitate.

SAMPLE QUESTIONS:

List 3 ways of making hard water Soft.