C3.2.1 Hard and soft water Flashcards
What happens when soap is used with soft water?
It lathers easily.
What happens when soap is used with hard water?
It forms scum.
What happens when soap-less detergent is used with hard water?
It does not form scum.
What dissolved compounds does hard water contain?
Calcium or magnesium compounds.
How does hard water gain the dissolved compounds?
When the water comes into contact with certain rocks.
What determines the hardness / softness of water?
The types of rocks found in different regions determines how hard or soft the water will be.
What is permanent hard water?
Permanent hard water remains hard when it is boiled.
What is temporary hard water?
Temporary hard water is softened by boiling.
How would you use titration to measure the hardness of water?
Take a known volume of water.
Slowly add soap solution from a burette or pipette.
Swirl the mixture + measure how much soap solution was required to form a lather.
The harder the water, the more soap solution required.
What causes temporary hard water?
Dissolved hydrogen carbonate ions.
How does boiling temporary hard water remove the hardness?
When heated, hydrogen carbonate ions break down to produce carbonate ions.
The carbonate ions react with dissolved calcium and magnesium ions to form insoluble precipitates.
Calcium carbonate and magnesium carbonate (limescale)
What causes permanent hard water?
Dissolved sulfate ions
Why does boiling not affect permanent hard water?
The sulfate ions do not decompose when heated -
they remain dissolved
Give 3 benefits of using hard water.
Can improve the taste of the water
Good for the development and maintenance of bones and teeth
Can help to reduce heart disease
Give 2 drawbacks of using hard water.
More soap is needed to produce lather, which increases costs.
When temporary hard water is heated it can produce limescale that reduces the efficiency of heating systems and kettles.
