What is hard water? advantages and disadvantages of hard water.

What is hard water?

advantages and disadvantages of hard water. 

Hard water

Find it difficult to make a lather with soap.

Bits of white scum will float around in the water when you use soap.

However, it does have its advantages.

Look at this table:

Disadvantages of hard water

Difficult to form lather with soap.

Scum forms in a reaction which wastes soap.

Scale (a hard crust) forms inside kettles.

This wastes energy when you boil your kettle.

Hot water pipes fur up' on the inside. The scale formed can even block up pipes completely.

 

 

Advantages of hard water

Some people prefer the taste.

Calcium in the water is good for children's

teeth and bones.

Helps to reduce heart illness.

Some brewers like hard water for making beer

A coating of scale (limescale) inside copper or lead pipes stops poisonous salts dissolving into our water.

 

Let's see if we can find out why some water is hard:

Experiment 22.1 What causes hardness in water?

Use 10 cm of each solution.

Add 1 cm" of soap solution to your boiling tube.

Put a bung in and shake.

See if you get a good lather (one that lasts 30 seconds).

A good lather means that the solution is soft.

A poor lather and white bits (scum) in your solution

means that it is hard.

 

What makes water hard?

If your water supply has flowed through chalk or limestone (calcium carbonate) it will be hard.

Other rocks which contain calcium or magnesium also cause hardness. Gypsum (calcium sulfate) is an example.

Calcium (or magnesium) compounds dissolved in water make it hard.

Calcium sulfate is slightly soluble in water. When a river flows over gypsum, it dissolves some of the rock.

Therefore. calcium ions get into the water as Ca (aq).

 

However, calcium carbonate is not soluble in water.

Water does not dissolve chalk or limestone rock.

But do you remember from page 109 how

limestone caves are formed?

People often think that rainwater is the purest water you can get. This isn't quite true.

On its way down, gases dissolve in the rain.

One of these gases is carbon dioxide - a weakly acidic gas.

It's the bubbles you see in fizzy drinks:

 

 

look at the state symbols in the equation above.

you can see that the calcium ions formed are soluble in water.

Therefore the calcium gets into the water, making it hard.

 

Assignment

 

Rainwater is the purest water. Is it true or false? Explain.   

 

                 Assessment

 

1.   Calcium in the -------------------- is good for children.

A.  Car

B. water

C. Mobile

 

2.   Scum forms in a reaction which wastes -----------.

A.  carbon monoxide

B.  methane

C. soap

 

3.   Calcium (or magnesium) compounds dissolved in water make it---------.

A. hard

B.  blue

C. pink   

 

4.   Calcium sulfate is slightly soluble in -------------------.

A. water   

B.  sol

C. alcohol

 

5.   calcium carbonate is not soluble in -----------------.

A. water   

B.  sol

C. alcohol

 

6.   A --------------------------- is an area from which water is drained.

A.  Evaporation 

B.  watershed

C. Precipitation

 

 

1.   Bits of white scum will float around in the water when you use soap.

A. True

B.  False

2.   Water is filtered through layers of stones and gravel to make sure all solids are removed.

A.  True

B. False

3.   The scale formed can even block up pipes completely.

A. True

B.  False

4.   Rainwater is the purest water.

A.  True

B.  False

5.    A coating of scale (limescale) inside copper or lead pipes stops poisonous salts dissolving into our water.

A. True

B.  False