Water

Question 0

What does hard water contain?

Answer 0

dissolved calcium and magnesium ions

Question 1

What type of water require little soap to form a lather?

Answer 1

soft

Question 2

Describe the formation of hard water

Answer 2

water with dissolved CO2 = acidic water

rain water flows over carbonated rocks and reacts with them so compounds from rocks dissolve into water

Question 3

What is scum?

Answer 3

insoluble precipitate

Question 4

How does scum form?

Answer 4

dissolved calcium and magnesium ions in hard water react with soap to form scum.

Question 5

Why is more soap needed to form a lather in hard water?

Answer 5

in order for lather to form all ions must have reacted with soap. Hard water has higher concentration of ions so require more soap

Question 6

Why are soap less detergents used?

Answer 6

they don’t form scum with hard water so can be used to wash clothes to prevent scum sticking to clothes

Question 7

What is scale?

Answer 7

insoluble solid

Question 8

How is scale produced?

Answer 8

when temporary hard water is heated

Question 10

Why is scale bad?

Answer 10

reduced efficiency of heating element because energy wasted heating up scale

Question 11

Give positive evaluation points of hard water

Answer 11

calcium ions are good for bones and teeth

calcium ions linked to preventing heart disease

Question 12

give negative evaluation points of hard water

Answer 12

more soap needed to form lather

produced scale which reduced efficiency

Question 13

Give two methods of softening hard water

Answer 13

Add sodium carbonate

ion exchange columns

Question 14

What is washing soda

Answer 14

sodium carbonate

Question 15

Which types of hardness does adding sodium carbonate soften?

Answer 15

both permanent and temporary

Question 16

How does adding sodium carbonate softening hard water?

Answer 16

sodium carbonate reacts with calcium ions/magnesium ions to form solid calcium/magnesium carbonate which is insoluble and can’t react with soap.

However these precipitates form lime scale

Question 17

How do ion exchange columns soften hard water?

Answer 17

cylinder packed with resin beads.
resins beads have sodium or hydrogen ions attached
As hard water passes through column the calcium and magnesium ions swap places with sodium or hydrogen ions.

Question 18

How can temporary hard water be softened?

Answer 18

heating it.

Temporary hard water contains hydrogencarbonate ions which, when heated, decompose to form carbonate ions, water and CO2.
Carbonate ions react with calcium and magnesium ions in water to form insoluble precipitates (calcium/magnesium carbonate = limescale)

Question 19

What are the steps involved in treating water to make it safe to drink?

Answer 19

Sedimentation and filtration - remove solids

disinfection - kill microbes

Question 20

What can chlorine be used for?

Answer 20

kill microbes in drinking water

Question 21

How can the taste of water be improved?

Answer 21

Water filters.
Contain silver to kill bacteria
Carbon to absorb impurities
Ion exchange resin too often water and remove heavy metal ions

Question 22

How can pure water be made and what are the drawbacks of it?

Answer 22

distillation:
Heat water so it evaporates
Water vapour passes through tubes
cooled down so condenses back into water

requires large amount of energy to boil water so expensive on large scale

Question 23

Evaluate adding fluoride to water

Answer 23

+ reduces tooth decay
+ only added in tiny amounts
- unethical
- linked to tooth staining

Question 24

What happens if ion exchange column runs out of sodium?

Answer 24

add sodium chloride ( dishwasher salt)

Question 25

How can insoluble solids be removed?

Answer 25

filter it through filtration beds

Question 26

How can dissolved salts be removed?

Answer 26

water filters containing carbon, silver and ion exchange resins

Question 27

How can microbes/ bacteria be removed?

Answer 27

adding chlorine

Question 28

How can hardness be measured?

Answer 28

titration:

add volume of water to conicle flask
add soap solution via pipette or burette
Swirl mixture
Record volume of soap solution required to form permanent lather