2.7 - Water Flashcards
How to test between hard and soft water
- place water in a boiling tube
- add soap solution and shake to see if a lather forms within 30 seconds
- if no lather forms keep shaking
- soft water needs a little soap to form lather whereas hard water needs a lot
Advantages of living in a hard water area
- strengthens teeth and bones
- reduces heart disease
Disadvantages of living in a hard water area
- limescale
- blocks pipes
Describe the stages in purifying water
- sedimentation where the larger solid particles settle at the bottom
- filtration where the water is extracted from the reservoir and is filtered to remove smaller particles
- chlorination where the bacteria is not removed through filtration so chlorine is added to the water to kill bacteria
Uses of water
- for factories in cooling machinery
- hygiene
- farms to grow food
- drinking water
How can we decrease water use?
- use washing machines and dish washers only when full
- have showers
- repair dripping taps
- use waste water for washing cars
- don’t let water to run excessively
Describe desalination
- process that removes minerals from salt water
- boiling is used but there has to be a nearby sea and it is costly
Explain chromotography
- to separate pigments in ink
- spots of colours are placed on pencil line
- dish of water (solvent) is raised until the paper comes into contact with the water surface
- the chromotogram develops
- most soluble substance travels the furthest
Explain gas chromotography
Can give the amount of substance present
-use this method to identify the amount of pollutant in the air or illegal drug in blood
How does temperature affect solubility
The higher the temp, the more solute will dissolve until a saturated solution forms (solution that cannot dissolve anymore solute into it)
Describe sedimentation
Where the larger solid particles will settle to the bottom
Describe filtration
Where the water is extracted from the reservoir, and is filtered to remove smaller particles
Describe chlorination
Where because the bacteria is not removed through filtration, chlorine is added to the water to kill the bactiera
Explain distillation with ethanol
- separates water and miscible liquids
- ethanol boils at 78C and water and ethanol are miscible
- in a mixture of ethanol and water, the ethanol would boil and evaporate first( lower boiling point) leaving water behind
- would condense on the cold wall of the condenser
Why is some water hard?
From rainwater passing along limestone, calcium ions will collect in the water. Ions such as magnesium ions will also collect in the water which makes the water hard
How to use soap to tell of water is hard or soft
Soap in hard water does not readily lather but scum is formed
Advantages and disadvantages of hard water
Ad: - strengthens teeth
- reduces risk of heart disease
- some people prefer the taste
Dos: -more soap is needed
- limescale can make them less efficient at boiling water
- hot water pipes can be blocked up with limescale
dis of desalination
- uses lots of energy
- expensive
- plants produce greenhouse gases
Describe an experiment to see if hard or soft water forms
- place 10cm of water in boiling tube
- add 0.5cm of soap solution and shake for 10 seconds to see if a lather forms that lasts 30 seconds
- if no lather forms add more soap
- record the volume needed to form a soap
Difference between hard and soft water
Soft- no Ca or Mg ions present
Hard- Ca or Mg ions present
Experiment to see if water is permanently hard or temporarily
- boil samples
- if the water is still difficult to lather then it is permanently hard
What compound does temporary hard water have that permanently doesnt
Hydrogencarbonate
How to remove permanent hardness by washing soda
- Add sodium carbonate (washing soda) which produces calcium carbonate so the calcium ions are removed as solid CaCo3 making thw water softer
How does an ion exchange column remove hardness in water?
-when the hard water is passed along negatively charged particles in the container, the positive ions of magnesium and calcium are attracted and are held there and are replaced with sodium ions, so the water leaves the container soft
