Water

Question 1

What do hard and soft water react with soap to form?

Answer 1

soft water readily forms lather from soap

hard water forms scum so more soap is needed to form a lather

soapless detergents don’t form scum

Question 2

What does hard water contain?

Answer 2

dissolved compounds, usually calcium or magnesium

compounds are dissolved when the water comes into contact with rocks

Question 3

What are the different types of hard water?

Answer 3

permanent - remains hard when boiled

temporary:

• softened by boiling,
• contains hydrogen carbonate ions (HCO3 ¯)
• these thermally decompose to produce carbonate ions which react with calcium and magnesium ions to form percipitates

Question 4

What is the problem with using hard water?

Answer 4

increase costs because more soap is needed to form a lather

when temporary hard water is heated it can produce scale that reduces the efficiency of heating systems

Question 5

What are the benefits of using hard water?

Answer 5

calcium compounds are good for the development and maintenance of bones and teeth and reduce heart disease

Question 6

What is another way of softening hard water?

Answer 6

dissolved calcium and magnesium ions can be removed by:

1) adding sodium carbonate, reacts with calcium/magnesium ions to form a precipitate of calcium/magnesium carbonate
2) using commercial water softeners such as ion exchange columns containing hydrogen/sodium ions, these replace the calcium/magnesium ions when hard water passes through the column

Question 7

What should human drinking water contain?

Answer 7

correct water quality is essential for human life

drinking water should have sufficiently low levels of dissolved salts and microbes

Question 8

How water of the correct quality produced?

Answer 8

using an appropriate source

passing water through filter beds to remove solids

sterilised with chlorine

Question 9

What do water filters contain?

Answer 9

carbon/silver ion exchange resins that remove some dissolved substances to improve taste and quality

silver reduces microbes

Question 10

How can pure water be produced?

Answer 10

pure water can be produced by distillation however it is expensive

Question 11

What are the other ways of making water more pure and what are their advantages/disadvantages?

Answer 11

chlorine can be added to remove bacteria

however chlorine also may cause harm to humans, especially when in contact with eyes or lungs

fluoride ions could be added to water as it improves bone density and reduces tooth decay

however, people should have a choice of what they consume