C3.2 Water
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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