Unit 2, topic 2 HARD WATER

Question 0

Physical properties of water are (6):

Answer 0

1) colourless and odourless
2) neutral (pH 7)
3) dissolves many substances
4) melting point of 0 degrees
5) boiling point of 100 degrees
6) density of 1g/cm 3

Question 1

Two steps in water treatment plant:

Answer 1

1) Filter

2) Chlorination

Question 2

Liquid to gas

Answer 2

evaporation

Question 3

gas to liquid

Answer 3

condensation

Question 4

solid to liquid

Answer 4

melting

Question 5

liquid to solid

Answer 5

freezing

Question 6

solid to gas

Answer 6

sublimation

Question 7

gas to solid :-)

Answer 7

chambersification

Question 8

desiccants is ….

Answer 8

substance which absorbs water from air

Question 9

what is deliquescent?

Answer 9

substances which absorb so much water from the air that they dissolve in it.

Question 10

Anhydrous copper sulfate powder turns from…

Answer 10

….from white to blue.

Question 11

Anhydrous cobalt chloride turns from what to what?

Answer 11

it turns from blue to pink

Question 12

definition of hard water

Answer 12

Hard water is water which does not lather readily with soap because of the presence of magnesium and calcium ions.

Question 13

sodium stearate is …

Answer 13

a common soap.

Question 14

why does hard water waste soap?

Answer 14

Because the sodium stearate combines with the calcium ions to form insoluble calcium stearate which appears as waxy scum.

Question 15

Disadvantages of hard water (2):

Answer 15

1) wastes soap

2) leaves fur or scale on kettles and pipes, causing a loss of efficiency and a potential blockage.

Question 16

Advantages of hard water (4):

Answer 16

1) Tastes better for brewing beer
2) necessary for tanning leather
3) good for teeth and bones
4) helps prevent heart disease

Question 17

Temporary hardness is….

Answer 17

hardness which can be removed by boiling.

Question 18

Permanent hardness is…

Answer 18

hardness which cannot be removed by boiling

Question 19

temporary hardness is caused by the presence of….

Answer 19

hydrogencarbonates of calcium or magnesium

Question 20

Permanent hardness is caused by…

Answer 20

sulfates or chlorides of magnesium or calcium

Question 21

true or false? Permanent hardness is harder than temporary hardness.

Answer 21

False, the hardest sample of water contains the highest concentration of Ca 2+ / Mg 2+ ions regardless of source

Question 22

What is the main cause of temporary hardness?

Answer 22

Dissolved Calcium carbonate

Question 23

How is dissolved calcium carbonate formed?

Answer 23

It is formed when rainwater, which is a weak acid, reacts with calcium carbonate in limestone rock.

Question 24

Which way round are stalagmites and stalactites?

Answer 24

Stalagmites grow up from the ground | Stalactites hang from the ceiling

Question 25

What can be softened by removing what?

Answer 25

The cause of hardness, ie calcium or magnesium ions

Question 26

How can water be softened? (3)

Answer 26

1) Boiling - decomposes hydrogencarbonates 2) Adding washing soda - precipitates calcium ions 3) Ion exchange

Question 27

Washing soda crystals contain what?

Answer 27

They contain hydrated sodium carbonate

Question 28

Explain what happens when washing soda is added to hard water.

Answer 28

The carbonate ions from the washing soda combine with the calcium ions from the hard water to form insoluble calcium carbonate which precipitates out of the solution.

Question 29

What is an ion exchanger?

Answer 29

It is a container full of small beads [resin] with sodium ions weakly attached to it.

Question 30

How does an ion exchanger work?

Answer 30

When hard water flows through the calcium ions in it switch places with the sodium ions and attach themselves to the resin The sodium ions are now in the water and the calcium ions on the resin.