C3.2 Water Hardness Flashcards
Why is rainwater naturally acidic?
Rainwater contains carbonic acid formed where water and carbon dioxide react
What is hard water?
Hard water forms when naturally acidic rainwater falls on rocks and minerals and dissolves compounds into the water
usually magnesium and calcium compounds
What’s the formula to create soluble calcium hydrogencarbonate?
carbonic acid + calcium carbonate → calcium hydrogencarbonate
Which ions make water hard? ;)
Calcium and magnesium ions make water hard when they are present
Which hardness of water forms a lather with soap easily?
Soft water
How is scum formed?
Scum forms when the dissolved calcium and magnesium ions react with soap and so more soap is needed when using hard water
In what regions is water harder?
The midlands / south east
Lincoln, London, Bristol, Southhampton, Brighton
Where is water softer?
The north west
Leeds, Manchester, Birmingham
YORKSHIRE, doncaster
How can you measure the hardness of water?
You can use TITRATION with a soap solution
The greater the amount of soap solution to form a permanent lather, the harder the water
How can you soften temporary hardness?
By boiling the water
Why does boiling remove temporary hardness?
Temporary hard water contains dissolved hydrogen carbonate ions.
When boiled, these decompose and form carbonate ions that react with the dissolved magnesium and calcium ions
This forms an insoluble precipitate that can be removed and the hardness is removed
What are the benefits of hard water?
- Improved / acquired taste (YORKSHIRE TEA)
- Calcium ions are good for development of bones and teeth
- Can help reduce risk of heart disease
What are the drawbacks of Hard water?
- More soap is needed to produce lather, more costs
- The scum produced is unsightly and ruins sexy bath time
- The insoluble precipitate causes limescale that ruins kettles, pipes, etc
How can you soften hard water?
By removing the calcium and magnesium ions
What are the two methods of softening hard water?
- Adding sodium carbonate
- Ion exchange columns
How can you soften hard water by adding sodium carbonate?
Sodium carbonate = washing soda
The insoluble sodium carbonate reacts with the calcium ions to create insoluble precipitates
These precipitates form limescale :(
How can you soften water using ion exchange columns?
Bead ion exchange resins are packed into an ion exchange column
The beads have sodium ions attached, these are swapped for calcium and magnesium ions as the water passes through
The water now doesn’t contain calciium or magnesium ions
It can become saturated with magnesium and calcium ions and so it needs to be regenerated by adding sodium chloride
Convenient + cost effective
How are ion exchange columns used commercially?
Dishwashers
In what ways is water purified?
- Adding fluoride
- Filtered (improve quality + taste)
- Distilled ( sea water to drinking water)
How is drinking water of sufficient quality produced?
- Supplied from an appropriate source
- Filtered
- Chlorinated
Where are appropriate sources of water?
Lakes, Rivers, Aquifers, Reservoirs
What is an aquifer?
An aquifer is an underground layer of permeable rock, gravel or sand that is soaked with water
After filtration, what occurs to water in a sedimentation tank?
Aluminium sulphate is added in order to clump together the tiny particles that were too fine for the filtration
The mixture is then passed through another fine filter system
How can you remove microbes from water?
eg disease causing microbes such as Typhoid and cholera
Chlorine kills microbes in the water
What are the benefits of adding fluoride to the water supply?
Improved dental health by reducing tooth decay
Why would people not want fluoride added to the water supply?
- It has been linked to tooth staining and bone disease
- Doesn’t allow people to have the choice of if they want it or not (unethical)
What do filter cartridges in a commercial / at home filtering device contain?
- Silver to kill bacteria
- Carbon to absorb impurities (eg chlorine)
- Ion exchange resins to soften water
How can salt water be made safe to drink?
DISTILLATION
Salt water is boiled, the condensation is cooled and collected
(salt is removed)
What are the disadvantages of distillation?
- Expensive due to needing a lot of energy
- Uses fossil fuels
- Carbon dioxide contributes to global warming
Why is distillation common in the middle east?
There is little rainfall but the countries are wealthy due to oil supplies
How can you test the purity of water?
Measuring its boiling point ( 100 = pure) Evaporating it ( No salt etc left = pure)
