Water Flashcards
What does hard water contain?
Lots of calcium and magnesium ions.
How does rainwater become hard?
Rainwater is weakly acidic.
When the rain falls, it flows over rocks.
Compounds from the rocks dissolve into the water.
Hard water contains dissolved compounds, usually calcium or magnesium compounds.
Why is hard water good?
Can improve the taste of the water
Are good for the development and maintenance of bones and teeth
Can help to reduce heart disease
What is temporary hard water caused by?
Hydrogencarbonate
How can you make temporary hard water soft?
By boiling it,
When heated, the calcium hydrogencarbonate decomposes to form calcium carbonate which is insoluble
This is the limescale on your kettle.
Whats the equation for the boiling of temporary hard water
Calcium hydrogencarbonate —> calcium carbonate + water + carbon dioxide
Whats bad about hard water?
Takes more soap to make a lather which is more expensive,
Forms a scum,
Limescale in a kettle makes it take longer to boil.
Scale can block pipes.
What is permanent hardness caused by?
Calcium sulfate.
How can hard water be softened by adding washing soda (sodium carbonate) to it.
The added carbonate ions react with the calcium and magnesium ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate.
Since the ions are no longer dissolved in the water so they can’t make it hard.
How can water be softened through an ion exchange column?
They have resins,
Which contain sodium ions which exchange for the calcium and magnesium ions in the water.
Whats the pros and cons of using an exchange column?
Pros:
Cheap, cost effective.
Cons:
Increase in sodium content
Why does water need to be treated?
It must be free of poisonous salts and harmful diseases.
How is water purified?
Passes through a mesh screen to remove twigs etc.
Chemicals are added to make solids and microbes stick and sink to the bottom.
The water is filtered through gravel beds.
Water is chlorinated to kill harmful microbes.
How do commercial filters remove substances from tap water?
The filters contain carbon or silver.
The carbon removes the chlorine taste and the silver kills bacteria.
Pros and Cons of adding chlorine and Fluorine to the water
Pros:
Fluorine reduces tooth decay,
Chlorine prevents disease.
Cons:
Chlorine could react with other substances and create toxic by products which could cause cancer.
High doses of fluoride can cause cancer and bone problems.
