Water Flashcards
How does calcium/magnesium dissolve into the water?
Water runs over rocks containing these elements
What makes water hard?
Dissolved calcium/magnesium ions
What are the advantages of hard water?
Calcium is good for bones
Can reduce risk of heart disease
What are the disadvantages of hard water?
Harder to form lather
Causes scum
Causes scale
What does permanent hard water contain?
Calcium salt (usually calcium sulphate) that is not removed when boiling
What are the two types of hard water?
Temporary
Permanent
How is scale formed?
When heated, the hydrogencarbonate decomposes to form carbonate ions
Carbonate ions react with magnesium/calcium ions to form calcium/magnesium precipitate
How do you distinguish between types of hard water?
Soap solution is added until permanent lather is formed
Same amount of each sample is boiled
Soap solution is added until permanent lather is formed
Temporary hard water should use less soap
How can hard water be softened?
Ion exchange resin
Soap
How does adding soap soften water?
Carbonate ions react with calcium/magnesium to form a precipitate of calcium/magnesium carbonate
How do ion exchange resins soften water?
Contains sodium ions which replace the calcium/magnesium
Resin has to be replaced when it runs out of sodium ions
How is water distilled?
Water is boiled to produce steam
Condensed to produce pure liquid water
Uses lots of energy so is expensive
Why is chlorine added to water?
Reduce amount of microbes
Why is fluoride sometimes added to drinking water?
Improve dental hygiene
How is water treated?
Passes through screen to catch large objects
Sand and soil settle out in settlement tank
Aluminium sulphate and quick lime is added to make dirt clump together so sink
Filter to remove mud or grit
Chlorine added to kill bacteria
pH level is checked
