Slides in this set

Slide 1

Preview of page 1

GCSE Chemistry 3:
Unit Two: Water…read more

Slide 2

Preview of page 2

C3 2.1: Hard Water
In areas where there is soft water, it is easy to form a rich, thick lather with soap.
In areas where there is hard water, it is more difficult to form a lather with soap. So, it is more difficult for people in these areas to wash themselves.
Hard water contains compounds that react with soap to form scum, which floats on water and sticks to the bath.
Scum formed by hard water is not a problem when washing clothes because we use more modern detergents called `soapless detergents'.
Most hard water contains dissolved magnesium and/or calcium ions. These get into the water when river water flows by rocks like gypsum (calcium sulfate),
which deposit the metal ions into the water.
Limestone (calcium carbonate) causes hardness in water.
Acid rain can make river water ever so slightly acidic.
The combination of the weakly acidic water and calcium carbonate forms calcium hydrogen carbonate, which is soluble in water, which makes the water
Using hard water is expensive because some of the soap is initially wasted reacting it with the calcium and/or magnesium ions in the water to form the
insoluble scum.
Limescale is formed when one type of hard water is heated. Limescale can be formed in kettles and washing machines for example. Pipes can be blocked
up and kettles can become a lot less efficient because limescale is not a very good conductor, so extra heating is required to boil water, so more energy is
needed and thus costs are more expensive.
Hard water can be good because it contains calcium which is good for the teeth and bones; it helps them grow stronger. Also, it has been proven that hard
water can help the heart.…read more

Slide 3

Preview of page 3

C3 2.2: Removing Hardness
Some scientists think we should drink hard water because it is good for your health
Softening water has many benefits. It does not form scum and scale is not formed during boiling of water (in kettles for example). A
lather is formed more easily, saving water and soap, and overall saving money.
Hard water makes industrial processes more expensive to run due to extra energy required to heat things...
Temporary hard water is hard water that can have its hardness removed through boiling. During this process, scale is formed and the
sole calcium/magnesium ions are removed. In this process, the hard water's hydrogencarbonate ions thermally decompose into
carbon dioxide, water and a carbonate. Then, the calcium/magnesium reacts with the carbonate to form calcium/magnesium
carbonate, thus removing the `hardness'. This is a waste of energy and very expensive.
Permanent hard water is hard water that has its calcium/magnesium ions in the water in the form of salts (like fluorides, chlorides, and
sulfates). It can be softened despite the name.
Another way to remove hardness is by adding sodium carbonate (washing soda). The washing soda forms calcium/magnesium
carbonate ions, which precipitate out the calcium/magnesium ions. The calcium/magnesium carbonate ions are insoluble so they can
easily be filtered out. This reaction is similar to the formation of scale to get rid of `hardness' in temporary hard water, but this is a lot
quicker and saves more money.
We can also use an ion-exchange column to remove `hardness'. This contains a resin packed with Na+ ions. The hard water is passed
through this column, where the hard calcium/magnesium ions are exchanged with the sodium ions in the resin. Sodium ions do not
cause `hardness' in water. Ion-exchange column resins need to be topped up with common salt (sodium chloride) to replenish the
sodium ions in the resin. Some exchange columns contain hydrogen instead of sodium ions.…read more

Slide 4

Preview of page 4

C3 2.3: Water Treatment
Water that has been passed through boreholes has most of the physical objects of it removed, but microbes
are still present, making it unsafe to drink.
Water from rivers and reservoirs requires lots of treatment before it is safe to drink.
Some people have filter jugs at home. These filter jugs have activated carbon, an ion-exchange resin, and
silver. The activated carbon is used to reduce chlorine levels, and also pesticides etc. The ion-exchange
resin is used to soften the water, through removing the calcium/magnesium ions as well as lead, copper and
magnesium ions. The silver in some filter jugs is used to discourage the growth of bacteria in the water. Most
filter jugs need their filter changing every few weeks.
Water that is fit to drink does not need to be pure. Most clean water drunk around the UK is just cleaned,
filtered water.
We can make pure water through distilling it. The steam can then be collected and condensed into liquid
water. This pure liquid water contains ONLY water and is used in science labs because it does not
unexpectedly react with any reactants in the lab.
We don't purify water in the industry because it requires heavy amounts of heat, which is extremely
expensive. So, we just use the filtering process.…read more

Slide 5

Preview of page 5

C3 2.4: Water Issues
You use money to buy a water softener and buy salt to top it up.
However, you save money using products you add to your heating system or washing machine. These products protect your
machines from scale, which could save you money on repairs that you would not need!
Hard water is proven to be good for your teeth and bones, whilst also being said to prevent heart disease.
Chlorine usage in water is good because it kills microbes that kill 5000 people a year through infected water.
Poisonous chlorine compounds could end up in water, so scientists need to monitor chlorine levels carefully.
Some people think that chlorine is bad for their health, so they try to remove it from the water.
Ozone is an alternative to using chlorine in water.
Some water supplies have fluoride ions added to them.
The advantages of fluoridation are: Better for fighting tooth decay; fluoride has not caused many problems in the past; fluoride
is only added in tiny amount (1ppm); fluoridation helps those who don't have great dental hygiene.
The disadvantages of fluoridation are: Fluorosis could occur on teeth and bones, where white streaks appear and could get
stained; the benefits of fluoridation are not significant, so there really is not need for the extra effort; it is ethically wrong to give
people treatments they have not consented towards; some studies show that excess fluoride is bad for the brain (diseases like
Alzheimer's); you cannot set a safe fluoride limit because people drink different amounts of water.…read more


No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »