Define Aeration Sedimentation Filtration Chemical purification.

Define Aeration Sedimentation Filtration 

Chemical purification.

 

 

Drinking water

Did you know that about two-thirds of the mass of your body is made up of water?

 

So it's not surprising that we should drink between 6 and 8 glasses of water everyday.

You don't want to shrivel up like a dried prune.

We are lucky that we have drinking water 'on tap.

Many people around the world have to collect their own water, often from contaminated sources.

We looked at the important job that chlorine does in making water safe to drink on page 55.

Now we can follow the journey of water, from a reservoir to our taps at home.

Let's look at the ways we treat water to make it safe to drink:

Aeration

The water is stirred up to let air (oxygen) mix with it.

This can also be done by letting it fall down steps.

This helps to remove iron(l|) ions in the water. They precipitate out

as iron(III) hydroxide. If this happens in your water at home, iron(III) hydroxide causes vegetables to turn brown

tea to have an inky colour and a bitter taste

clothes to get rusty stains after washing.

Sedimentation

Larger solid particles are allowed to settle at the bottom of the sedimentation tanks. But dirty water is a sol.

There are colloidal particles of clay dispersed in the water.

The tiny particles are electrically charged (negative).

They stay spread throughout the water because they repel each other.

So water companies add aluminium sulfate to coagulate the clay. The particles are attracted to the highly charged Al⁺ ions. They form clumps

which get heavy enough to settle on the bottom of the tank.

 

The acidity of the water is controlled using lime slurry.

This calcium hydroxide is alkaline so it raises the pH of the water. The aluminium sultate coagulant is good at removing alkaline substances.

Filtration

Then the water is filtered through layers of sand and gravel to make sure all solids are removed. These filter beds can also contain carbon slurry to get rid of substances that would give the water an odd smell or taste.

Chemical purification

Does your tap water ever smell of chlorine?

Chlorine is added to kill bacteria in the water.

This prevents diseases.

The water company will add enough chlorine to kill all the bacteria. But how would you like drinking water that tasted like it was from a swimming pool?

They remove any excess chlorine by treating the water with sulfur dioxide. This reacts with the chlorine, getting rid of its smell and taste.

The chlorine is reduced to chloride ions, Cl(aq).

A little chlorine is left in the water to keep it free from germs in the journey to your tap.

Class Assessment

 

1.   ----------------- on Earth Without depends on water.

A.  Car

B.  Life

C. Mobile

 

2.   About two-thirds of the mass of your body is made up of -----------

A.  carbon monoxide

B.  methane

C. water

 

3.   Iron(III) hydroxide causes vegetables to turn ------------------.

A. brown

B.  blue

C. pink   

 

4.   Dirty water is a -------------------.

A.  Evaporation  

B.  sol

C. Precipitation

 

5.   The acidity of the water is controlled using lime-----------------.

A.  slurry

B.  Condensation

C. Precipitation

 

 

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

A.  Evaporation 

B.  watershed

C. Precipitation

 

 

1.   Calcium hydroxide is alkaline so it raises the pH of the water.

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.   Remove any excess chlorine by treating the water with sulfur dioxide.

A. True

B.  False

4.   Chlorine is added to kill bacteria in the water.

A.  True

B.  False

5.   The chlorine is reduced to chloride ions.

A. True

B.  False