- All living things use water to sustain their lives.

- Human beings, for example, use water for irrigation, for washing, drinking, fish farming and transportation among other uses.

- In most cases, water has some dissolved particles in it.

Such water may not be suitable for drinking, cooking, and washing. Water can be classified either as soft or hard.

What kind of water can be classified as soft water? What about hard water?

 

Activity

Finding out the difference between soft and hard water. What you need:

• Water from different sources such as rain, sea, river, lake, borehole, tap, ocean.
• Clear plastic bottles.
• Small pieces of bar soap.
• Small basin.

 

 What to do

1. Collect water from different sources like tap, river, ocean, lake, sea, borehole and rain.
2. Pour the water from each different place into separate clear plastic bottles.
3. Label these bottles according to the source of water.
4. Observe the water closely by looking at it; feeling it between your fingers; smelling it. Which water is the clearest?
5. Now pour a small amount of tap water into a small tin. Put one piece of soap into the tin of water. Shake hard for five minutes. What do you notice?
6. Do the same with the remaining water samples.

 

Note

In all cases ensure that you use the same amount of soap and water and that you shake for the same period of time. What you have learned The water that formed lather with soap easily is said to be soft water. The water that did not form lather easily is said to be hard water. Water from sources such as borehole, sea or ocean, lake, well, tap and river are hard water. They have minerals dissolved in them which makes them hard. Rainwater and sometimes spring water is known to be soft water.

 

Difference between soft and hard water

The source of water determines whether the water is soft or hard. Some sources may contain salts while others may not contain salts.

• Water with salts dissolved in it is hard water. The salts found in the water are usually picked up from rocks, or the soil as water flows through them.
• Water that does not contain salts or that which has a very little amount of salt is known as soft water.

• Soft water easily forms lather with soap while hard water does not easily form lather with soap.

• Hard water therefore contains salts that dissolve in it as it flows from various places. Ocean water is the best example of hard water and rainwater is a good example of soft water.

 

Disadvantages of hard water

As we have learned, hard water does not easily lather with soap. Obviously, this is one of the disadvantages of hard water. When using hard water for washing, a lot of soap is used compared to when soft water is used.

The other disadvantages of hard water are as follows:

1. Hard water wears out clothing as vigorous rubbing is required to remove the dirt.
2. Hard water stains clothes. When soap is dissolved in hard water, scum is formed. The scum stains clothes being washed.
3. Hard water cause boiler scales in hot water pipes. The boiler scales may cause blocking of the pipes and spouts of kettle. Look at the image below:
4. Hard water causes the formation of fur on pans or sufurias. Fur is a poor conductor of heat and this leads to fuel wastage.
5. Hard water increases the rate of wearing out of utensils as the fur stain needs to be scrubbed.

Fact check

Activity

Finding out the effect of water hardness on the cleaning ability of soap. What you need :

• Two pieces of cloth.
• Sukuma wiki leaf or any other leaf.
• Rainwater or soft water.
• Sea or river or any other hard water.
• Two identical basins.

 

What to do

1. Stain two pieces of cloth with leaf juice by rubbing the sukuma wiki or leaf on to the pieces of cloth.
2. Put the rainwater and sea or river water in two identical basins and label them.
3. Wash out the stains from the pieces of cloth in the different containers using soap.

Questions  

• In which water did the dirt or stain come out with the least rubbing?
• In which water would clothes last shortest if cleaned often in it?

 

What you have learnt

Scum that forms when hard water is mixed with soap affects the cleaning power of soap. It reduces the effects of soap therefore a lot of soap has to be used and clothes need much more rubbing to remove dirt or stains.

Clothes cleaned in hard water might last for a shorter period since they have to be rubbed harder to remove the dirt or stain.

They also last for a short time because the minerals in hard water are rough on clothes.

When bathing, more soap is used if the water is hard than if the water is soft.

 

Activity

Finding out what happens when hard water is heated

What you need

• New and old pieces of hot water pipe.
• New and old electric kettle.

What to do

1. Examine the inside of new and old pieces of hot water pipes.
2. Look at the spout of the new and old kettles.
3. Now, look at the pictures of the spout of the new and old kettles given below.

Why is the diameter of the spout of the old kettle narrower than the spout of the new one?

Fur is a bad conductor of heat. It therefore reduces the amount of heat reaching the water. It takes much longer to heat the water leading to wastage of fuel.

 

Know more

Softening hard water by boiling

It is possible for hard water to become soft. This is done by removing the mineral salts that cause water hardness.

The process of removing mineral salts from hard water is called softening. Hard water can be softened in two ways:

• Boiling the hard water: this way, the minerals are left on the walls of the boiling container.
• Using chemicals: The addition of certain chemicals to the hard water makes the water to become soft. 

 

Activity

Softening hard water by boiling What you need:

• Tin.
• Sea or river water.
• Two pieces of bar soap.
• Two identical bottles.
• Two basins.

 

What to do

1. Boil some sea or river water in a tin and let it cool.
2. Measure some of the boiled water using a bottle and put it in a basin.
3. Measure the same amount of the unboiled water and put it in the second basin.
4. Now drop one piece of bar soap in each basin. Shake hard, for two to three minutes to produce foam. What do you observe?

What you have learnt

Lather is more easily formed in boiled water than in unboiled water.

Boiling changed hard water into soft water.

Hard water can be softened by boiling it.

However, not all hard water can be made soft through boiling.

Hard water which can be changed into soft water through boiling is said to show temporary hardness.

It is therefore referred to as temporary hard water.

Water that cannot be made soft by boiling shows permanent hardness.

It is known as permanent hard water. Permanent hardness in water can only be removed by the use of chemicals.

Below are some of the new words you have learnt in this topic.

Revision Exercise

1. Water can be said to be ________________ or _________________.

2. Name two sources of

   a) hard water.

   b) soft water.

3. Which of the following is NOT TRUE about hard water?

   A. Lathers very easily with soap.

   B. Forms scum with soap.

   C. It has mineral salts.

   D. Forms milky appearance with soap.

4. Which of the following is the name given to the dark-grey coating that forms in kettles and pans after boiling water?

  A. Boiler scale

  B. Scum

  C. Fur

  D. Lather

5. Temporary hardness in water can be removed by _________________.

6. Which of the following is NOT true about hard water?

  A. Damages hot water pipes.

  B. Uses less soap.

  C. Wastes soap.

  D. Damages clothes.

7. How does hard water affect the following?

  (a) Clothes   (b) Pipes   (c) Pans

8. What is scum and how is it formed?

What you have learnt

When hard water is heated, it forms substances that cannot dissolve in water.

When the heated water is passed through water pipes or through kettles, these substances are deposited on the pipes or spouts of kettles.

These substances are called boiler scale. Scales are the cause of pipes getting blocked.

Also, when you boil water on a sufuria or pan, you notice the inside of the sufuria or pan changes colour to pale-grey.

This is as a result of the formation of fur on the sufuria or pan.

 

KCPE Topical Questions

Standard 8

Hard and soft water

1. Pupils in Standard VII at Omeri Primary School were given different volumes of four clear samples of water labeled W, X, Y and Z. They boiled each sample in turn to evaporate all the water and then collected and weighed the solids that had remained. Their results were as shown below.

Water sample	Volume of water evaporated (cm3)	Amount of solid collected (g)
W X Y Z	50 100 200 300	2.5 2.0 5.0 3.0

Which one of the four samples would form lather with soap MOST EASILY?

A. W          B. X          C. Y           D. Z