3a.2 - Water

Question 1

What does hard water make?

Answer 1

Scum and scale

Question 2

How is scum produced?

Answer 2

Reacting soap with water

Question 3

How is scale produced?

Answer 3

When water is heated

Question 4

How do you get a lather from washing hands using hard water?

Answer 4

Use more soap

Question 5

What are the disadvantages of washing your hands in hard water?

Answer 5

More soap has to be used so more money needs to be spent to buy it

Question 6

Why is scale bad? (2)

Answer 6

• Reduces efficiency of appliances

- Can eventually block pipes

Question 7

What is water hardness caused by?

Answer 7

Ca2+ and Mg2+ ions

Question 8

How does water become hard? (2)

Answer 8

• Rainfall can dissolve compounds like magnesium sulphate

- and calcium sulphate

Question 9

What are the advantages to hard water? (2)

Answer 9

• Ca2+ is healthy foe teeth and bones

- People who live in hard water areas are less likely to develop heart disease

Question 10

What is temporary hardness caused by? (2)

Answer 10

• Hydrogencarbonate ion

- HCO3- (3 oxygen’s all -ve charge)

Question 11

What is permenant hardness caused by?

Answer 11

Dissolved calcium sulfate

Question 12

How is temporary hardness removed?

Answer 12

Boiling

Question 13

What happens when temporary hard water is heated? (2)

Answer 13

• The calcium hydrogencarbonate decomposes to form calcium carbonate
• which is insoluble

Question 14

What is the word equation for the removal of temporary hardness?

Answer 14

Calcium hydrogencarbonate -> Calcium carbonate + water + carbon dioxide

Question 15

What is the symbol equation removal of hard water?

Answer 15

Ca(HCO3)2 -> CaCO3 + H2O + CO2

Question 16

How can temporary and permanently hard water be softened?

Answer 16

By adding washing soda

Question 17

What is washing soda?

Answer 17

Sodium carbonate

Question 18

What is the chemical name for washing soda?

Answer 18

Na2CO3

Question 19

How does washing soda soften temporary and permanently hard water?

Answer 19

It reacts with the Ca2+ and Mg2+ ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate

Question 20

How can both types of hardness be removed?

Answer 20

Running the water through an ion exchange column

Question 21

How does an ion exchange column work? (2)

Answer 21

• The column columns contain lots of sodium or hydrogen ions

- and exchange them for the calcium and magnesium ions in the water

Question 22

What can you use to compare the hardness of water samples?

Answer 22

Titrations

Question 23

How do you do a titration? (6)

Answer 23

• Fill a burette with 50cm3 of soap solution
• Add 50cm3 of the first water into a flask
• Use the burette to add 1cm3 of soap solution to the flask
• Put a bung into the flask and shake for 10cm
• Repeat steps 3 and 4 until a lather is formed
• Record how much soap it took

Question 24

What is the first part of water treatment and why is it done?

Answer 24

• Screening

- Removes big parts like twigs

Question 25

What is the second part of water treatment and why is it done?

Answer 25

• Removal of solids and microbes

- Chemicals are added to make solids and microbes stick together and fall to the bottom

Question 26

What is the third part of water treatment and why is it done?

Answer 26

• Filtration

- Filtered through a gravel bed to remove the solids

Question 27

What is the fourth part of water treatment and why is it done?

Answer 27

• Chlorination

- Kills of harmful microbes

Question 28

Why do we not always drink distilled water?

Answer 28

• Too expensive to boil everything we drink

Question 29

What are the advantages to adding fluoride and chlorine to water?

Answer 29

• Fluoride reduces tooth decay

- Chlorine prevent disease

Question 30

What are the disadvantages to adding fluoride and chlorine to water? (3)

Answer 30

• Could cause certain cancers
• Could cause bone problems
• Levels of chemicals need to to be carefully monitored