C3.2 Water Flashcards
How is hard water produced from rain water?
calcium/magnesium ions dissolve from rocks (limestone)
What is formed when hard water reacts with soap
scum
State one health benefit of drinking hard water
- helps maintain bones
- helps maintain teeth
- helps reduce heart disease
Why is distillation generally not used to purify water
High cost of energy
Why is chlorine added to water
- kill microbes
- sterilise it
What in water filters reduce the hardness of water
Ion exchange column
Suggest why water filters contain particles of nanosilver
- kill microbes
- sterilise it
Describe the main two steps used to treat water from reservoirs
- filter
- to remove solids
- add chlorine
- to kill bacteria/sterilise it
A student boils some hard spring water in a pan.
The inside of the pan becomes coated with a white solid.
Explain how the white solid is produced.
- water contains calcium hydrogen carbonate (HCO3-)
- which decomposes
- to form calcium carbonate (or limescale)
Explain how an ion exchange column softens water
- Sodium ions (Na+) in <u>the resin</u>
- replace
- calcium ions(Ca2+)/magnesium ions (Mg2+)
Why do some companies add fluoride to the drinking water?
-Improve dental health (reduce tooth decay)
Describe how sodium carbonate is used to soften water
- sodium carbonate is added to hard water
- calcium ions precipitate out (form a solid)
- as calcium carbonate
- which can be filtered out of the water
How is scale formed?
- temporary soft water is heated
- hydrogen carbonate ions decompose
- to form carbonates
People who use hard water can expect higher costs than people who use soft water.
Explain why.
either
Forms scum
more soap is needed to form a lather
or
forms scale on heating
making kettles/heating systems less efficient
