C3.2 Water

Question 1

What happens when hard water reacts with soap?

Answer 1

scum is formed so more soap is needed to form lather

Question 2

What type of soap does not form scum when it reacts with hard water?

Answer 2

soapless detergents

Question 3

What does hard water contain?

Answer 3

dissolved compounds, usually of calcium or magnesium

Question 4

When do compounds of calcium or magnesium become dissolved in water?

Answer 4

when water comes into contact with rocks

Question 5

What are the 2 types of hard water?

Answer 5

temporary hard water

permanent hard water

Question 6

What is the difference between temporary hard water and permanent hard water?

Answer 6

permanent hard water remains hard when it is boiled whereas temporary hard water is softened by boiling

Question 7

Describe how temporary hard water is softened by boiling

Answer 7

temporary hard water contains HYDROGENCARBONATE IONS (HCO3-) that decompose on heating to produce carbonate ions which react with calcium or magnesium in the hard water to form precipitates- scale

Question 8

What are some disadvantages of using hard water?

Answer 8

can increase costs because more soap is needed

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

Question 9

What are some advantages of using hard water?

Answer 9

calcium compounds are good for the development and maintenance of bones and teeth and can also help to reduce heart disease

Question 10

How can hard water be made soft? (2 ways)

Answer 10

ADDING SODIUM CARBONATE- which reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate

USING COMMERCIAL WATER SOFTENERS- such as ion exchange columns containing hydrogen ions or sodium ions, which replace the calcium and magnesium ions when hard water passes through the column

Question 11

How can the correct water quality be produced by?

Answer 11

by:

• choosing an appropriate water source
• passing the water through filter beds to remove any solids
• Sterilising with chlorine

Question 12

For humans, what should water have significantly low levels of?

Answer 12

dissolved salts and microbes

Question 13

What do water filters contain?

Answer 13

carbon, silver and ion exchange resins

Question 14

What do water filters do?

Answer 14

they remove some dissolved substances from tap water

to improve the taste and quality

Question 15

How do water filters work?

Answer 15

carbon removes the chlorine taste and silver is suppose to kill bugs

Question 16

Why may chlorine be added to water?

Answer 16

to reduce microbes

Question 17

Why may fluoride be added to water?

Answer 17

to improve dental health

Question 18

What are some arguments against the addition of fluoride to drinking water?

Answer 18

high doses can cause cancer and bone problems

people do not think it is right to ‘mass medicate’ so should be able to chose whether they want to be taking fluoride

Question 19

What are some arguments against the addition of chlorine to drinking water

Answer 19

toxic

no consumer choice

Question 20

Pure water can be produced by…….

Answer 20

distillation

Question 21

Why does the distillation of water cost a lot?

Answer 21

because of the large amount of energy needed

Question 22

Describe how pure water can be produced by distillation

Answer 22

heat and boil water to make steam.

cool steam and allow it to condense

Question 23

What is the word equation for when temporary hard water is heated?

Answer 23

calcium hydrogencarbonate—calcium carbonate + water + C02

Question 24

What is limescale?

Answer 24

calcium carbonate

Question 25

Describe how you can measure the hardness of water by titration with soap solution

Answer 25

- Fill a burette with 50 cm3 of soap solution - Add 50cm3 of the first water sample into a flask - use the burette to add 1cm3 os soap solution into the flask - put a bung in the flask and shake for 10 seconds - repeat steps 1-4 until a good, lasting lather is formed (a lasting lather is one where bubbles cover the surface for at least 30 seconds) - record how much soap was needed to create a lasting lather - repeat all the steps with other water samples - repeat whole experiment again using boiled samples instead to see if the results change if the sample is temporary hard water

Question 26

What happens when soft water reacts with soap?

Answer 26

soft water readily forms a lather

Question 27

Describe how an ion exchange column softens water

Answer 27

the calcium ions in the water are replaced by sodium ions in the resin in ion exchange columns

Question 28

Explain why sodium chloride needs to be passed through an ion exchange column after the column has been used for a couple of weeks

Answer 28

to replenish sodium ions

Question 29

Suggests arguments for the addition of adding chlorine to sterilise water

Answer 29

- kills microbes - prevents disease - only small amounts are needed

Question 30

Explain how scale forms on heating elements

Answer 30

on heating, the calcium hydrogencarbonate ions decompose forming calcium carbonate which is insoluble

Question 31

Explain how adding sodium carbonate softens hard water

Answer 31

the carbonate ions react with calcium ions forming a precipitate of calcium carbonate therefore the water is softened as this removes the calcium ions which caused the water to be hard

Question 32

Suggest why scale on heating elements causes problems

Answer 32

the scale reduces the efficiency of the heating element this increases energy costs

Question 33

Explain how water filters containing carbon, silver and ion exchange resin softeners soften permanent hard water

Answer 33

sodium ions are present in the resin these sodium ions replace the calcium ions, which caused the hardness of water

Question 34

How is hard water produced from rainwater?

Answer 34

calcium or magnesium ions causing water hardness are dissolved from rocks

Question 35

What are some advantages and disadvantages of using an ion exchange column?

Answer 35

resin needs replenishment with sodium ions increases sodium content of the water easy/quick method continuous process

Question 36

What are some advantages and disadvantages of using sodium carbonate to soften water?

Answer 36

batch process leaves a residue of precipitated carbonate in the water increases sodium content of the water easy/cheap