Water

Question 1

Describe what is hard water and how it is formed

Answer 1

• Solution that contains high concentration of Calcium ions (or Magnesium ions.)
• Formed when water contacts rock and dissolves the ionic compounds in them.

Question 2

Describe the problems of hard water

Answer 2

Forms scum (solids/precipitate) when reacted with soap & requires more soap before a lather (lots of bubbles is formed)

Increase costs as more soap is needed

Heating hard water cause lime scale being formed on heating elements

Lowers the heating efficiency of element and increase energy costs.

Question 3

Permanent hard water

Answer 3

• Calcium sulfate – CaSO4
• Water remains hard even after boiling
• Will require lots of soap solution to lather BEFORE and AFTER boiling.

Question 4

Temporary hard water

Answer 4

• Water is softened by boiling (has less Calcium and magnesium ions)
• Temporary hard water contains hydrogen carbonate ions (HCO3-) which break down on heating and produce calcium and magnesium precipitates (solids).
• In kettles this precipitate is called lime scale (chemical name is calcium carbonate).
• Will require lots of soap solution to lather before boiling

but will require only a little volume of soap after boiling.

• Reduces the efficiency of kettles and heating systems and so would cost more in energy.

Question 5

Lime scale

Answer 5

Formed when hard water/calcium hydrogen carbonate is heated and produces calcium carbonate precipitate.

Question 6

Soft water

Answer 6

Low concentration of Calcium ions (and/or Magnesium ions.)

Forms lather easily with small volumes of soap solution.

Question 7

Soapless detergents

Answer 7

Soap that Do not form scum

Question 8

Problems/disadvantages of Hard water

Answer 8

Increase cost as more soap is needed

(lime) Scale reduces efficiency of heating system and kettles - increase energy costs

Question 9

Benefits/advantages of hard water

Answer 9

• Calcium good for development of bones and teeth

* Helps reduce heart disease

Question 10

Methods of softening hard water

Answer 10

• Adding sodium carbonate and filtering the calcium carbonate and magnesium carbonate precipitates.
• Ion exchange columns that contain hydrogen ions (H+) and sodium ions (Na+), which replace the calcium and magnesium ions when hard water passes through the column.
• Distilling to produce pure water

Question 11

Water for humans

Answer 11

Needs low levels of salt and microbes but does not have to be pure water.

Question 12

Method that water companies do to get water of good quality

Answer 12

• Choose appropriate source.
• Pass water through filter beds to remove solids
• Add chlorine to kill microbes
• Add fluorine to improve people’s teeth

Question 13

Why is fluorine added to water

Answer 13

improve peoples teeth

Question 14

why is chlorine added to water

Answer 14

to kill microbes

Question 15

how are solids removed from drinking water

Answer 15

Pass water through filter beds

Question 16

What are the three main parts of a Water filters and describe what eacha part does

Answer 16

• Contain carbon, silver nanoparticles and ion exchange resins

Carbon remove dissolved substances.
•
Ion exchange resin swaps Calcium ions, Ca2+ for sodium ions, Na+. making water soft
Silver nanoparticles kill bacteria.

Question 17

What does carbon in a water filter do?

Answer 17

remove dissolved substances.

Question 18

Why do people use water filters

Answer 18

Water filters improve taste.

Question 19

What does the ion exchange resin in a water filter do?

Answer 19

Ion exchange resin swaps Calcium ions, Ca2+ for sodium ions, Na+ - softens the water

Question 20

What does the silver nanoparticles in a water filter do?

Answer 20

kill bacteria.

Question 21

What does an ion exchange resin do and where is it used?

Answer 21

• A plastic filter that allows tap water to pass through it before it comes out the tap.
• Contains lots of sodium ions (Na+) that replace calcium ions or magnesium ions in hard water to make the water soft.

Question 22

Problems of ion exchange resins

Answer 22

May increase heart disease as it increase sodium ions in water.

Requires replacing regularly as the sodium ions need replacing.

Question 23

Pure water

Answer 23

• Water without anything dissolved.

* Produced by distillation