Hard WaterHard Water

L.O: To know what makes L.O: To know what makes water hard, and the pros and water hard, and the pros and cons associated with this cons associated with this

What do washing powder boxes tell What do washing powder boxes tell you about hard and soft water?you about hard and soft water?

Rain Water Rain Water All rain water is slightly acid due to the CO2

in the air but it is increased by …

CO2 – Burning fossil fuels and respiration (deforestation also reduces the earths ability to remove CO2) Carbolic Acid

SO2 – Volcanoes and Power stations Sulphuric Acid

N2 – Exhaust fumes Nitric acid

Acid rain kills plants and fish

As rain water runs over rocks it picks up other minerals

Running over the limestone also causes other salts to dissolve e.g. calcium and magnesium

Carbonic acid reats with limestone to create soluble calcium hydrogencarbonate Calcium carbonate (s) + Carbonic Acid (aq) Calcium hydrogencarbonate (aq)

CaCO3 (s) + H2CO3 Ca(HCO3)2(aq)

Water with these salts is called HARD WATER

Water without these salts in called SOFT WATER

Hardness can be temporary or permanent. Temporary hardness is dues to calcium hydrogen carbonate. Temporary hardness may be removed by boiling because hydrogencarbonate ions form carbonate ions which react with calcium or magnesium to form precipitates

Permanent hardness is caused by calcium and magnesium sulfates which cannot be removed by boiling

Permanent and Temporary Hardness

Which areas would you expect to have high proportions of limestone?

How could you How could you test how hard or test how hard or

soft water is?soft water is?

Prove the hypothesis that more soap is needed for harder water.And that boiling temporary hard softens the water

You will have water You will have water samples: samples:

softsoft

DistilledDistilled

Temporary Hard ATemporary Hard A

Boiled ABoiled A

Permanently Hard BPermanently Hard B

Boiled BBoiled B

10ml water, 1ml 10ml water, 1ml soap at a timesoap at a timeDesign a table to collect

quantitative results in

Tap water in some parts of the Tap water in some parts of the country is very pure and is country is very pure and is said to be ‘soft’. It easily said to be ‘soft’. It easily makes a lather with soap. makes a lather with soap.

Water from other parts may Water from other parts may contain various dissolvedcontain various dissolvedimpurities and is described as impurities and is described as ‘hard’ water. ‘hard’ water.

Temporary hardness may be Temporary hardness may be removed byremoved byboiling, but permanent boiling, but permanent hardness survives the boiling hardness survives the boiling process.process.

In this practical activity, water In this practical activity, water hardness can be measured by hardness can be measured by finding out the volume offinding out the volume ofsoap solution required to form soap solution required to form a permanent lather with a a permanent lather with a known volume of water.known volume of water.

Is the rainwater hard or soft?Is the rainwater hard or soft? 2. Is seawater hard or soft?2. Is seawater hard or soft? 3. Does seawater contain temporary hardness, permanent hardness or both?3. Does seawater contain temporary hardness, permanent hardness or both?

Water type to produce Volume of soap required a permanent lather /cm3

Rainwater 0.5

Seawater 4

Temporary hard water 3

Seawater, boiled thencooled (permanent hardwater)

3

Temporary hard water,boiled then cooled

1

HARD needs more soap!HARD needs more soap!

The compounds dissolved in hard water (Calcium ions) react with the soap, forming scum.

The soap makes scum before it can cause lather.

Sodium stearate (soap) + calcium ions calcium stearate (scum) + sodium ions

Hence harder water needs more soap.

HARD Vs SOFT WATER HARD Vs SOFT WATER HARD WATER

•Does not lather easily with soap so wastes soap and money

•Forms a scum with soap

•Causes limescale which can reduce the efficiency of appliances

•BUT contains chemicals good for health and development of teeth and bones and can reduce heart disease. Also tastes better and is better for making beer!!!

SOFT WATER

•Does not taste very nice

•Less health benefits

•BUT no limescale or scum and better for soap