Chemistry 3_ water.txt
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- Tap water contains....
- Dissolved substances e.g. calcium and magnesium (in hard water)
What is the difference between hard and soft water?
Hard water has more dissolved Ca and Mg
Water can be used...
- As a solvent
- A coolant
- In industrial processes
Main points of the water cycle:
ENERGY from the sun makes water EVAPORATE. It CONDENSES to form clouds. Temperature drops, RAIN falls onto land. RUNOFF accumulates back in the sea.
What does soluble mean?
A solid that dissolves on water
The solid that dissolves in water is called....
Why is water called a universal solvent?
Many substances dissolve in it
Solubility is measured in...
g/100g of water
Soluble or insoluble: most ionic compounds...
Soluble or insoluble: most covalent compounds
Soluble or insoluble: some molecular substances
How does temperature affect solubility of compounds?
Increased temperature means increased solubility
Explain HOW temperature effects solubility of compounds.
Liquid expands when heated so there is more room in there for solid particles
What does a solubility curve show?
The maximum amount of solute that can be dissolved in a solvent at a particular temperature to give a SATURATED SOLUTION
What happens if a saturated solution cools down?
Some solute crystallises out
How can you work out how much solute cryatallises out?
Solute at initial temp - solute at 'cooled down' temp = solute that crystallises out.
Solubility of gas increases as......
- Temperature decreases
- Pressure increases
Explain HOW solubility of gases is effected.
When liquids are heated they expand so it is easier for gases to escape
Give an example of when CO2 is used
In fizzy drinks under pressure. Opening the lid releases pressure which is why it would eventually go flat (gas would escape)
What gas dissolved in water is essential for aquatic life?
Give an example of how, related to water, power stations harm aquatic life.
The discharge of hot water means less oxygen can dissolve in the water in lakes so there is less oxygen for the aquatic life.
List the two main stages of drinking water
- The water is passed through a FILTER BED to remove solid particles
- CHLORINE GAS is added to kill harmful bacteria
How can water quality be improved?
- Using a filter which contains carbon, silver and ion exchange resins.
- Any water can be distilled but this used a lot of energy which makes it more expensive.
What type of water readily forms a lather with soap?
How do compounds get in hard water?
Water flows over rocks and compounds get dissolved in the water
Hard water with soap forms....
Scum. This makes it harder to form a lather.
Advantages of hard water
Good for your health
Disadvantages of hard water
- More soap is needed for lather, increases COST
- Deposits (scale) form on appliances e.g. kettles. This reduces efficiency.
List the two ways to remove hardness
- Add sodium carbonate
- Ion exchange column
Explain why sodium carbonate solution removes hardness
The carbonate ions react with the Ca and Mg (which make water hard) to make calcium carbonate and magnesium carbonate (respectively). These are both insoluble precipitates.
Explain what an ion exchange column does to remove hardness of water.
The resin supplies hydrogen or sodium ions. As the hard water passes through the Ca and Mg ions are replaced by the H or Na ions.
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