Water

Question 1

Hard water

Answer 1

Water that will not easily form a lather with soap.
Hardness caused by Ca2+ or Mg2+ ions dissolved in water
Grey precipitate(scum) often forms instead of soap

Question 2

Temporary hardness

Answer 2

Water hardness that can be removed by boiling the water

Question 3

Permanent hardness

Answer 3

Harness that can’t be removed by just boiling water

-caused by calcium sulfate(CaSO4) or magnesium sulfate(MgSO4)

Question 4

3 methods of removing harness from water…

Answer 4

• Distillation (boiling & then condensing the vapour)
• Washing soda (softens the water, carbonate ions in soda react with Ca ions in water)
• Ion exchange resin ( swaps out ions that cause hardness, e.g. Ca2+ for Na+)

Question 5

Complexometric titration

Answer 5

A titration involving the formation of a complex between metal ions & a reagent such as EDTA. The end point is marked by a sharp decrease in the conc. of free metal ions

Question 6

Buffer solution

Answer 6

A soln. that resists changes in pH, keeps pH constant

Question 7

Flocculation

Answer 7

The coming together (coagulation) of small suspended particles in water

Question 8

Flocculating agent

Answer 8

A chemical added to water to coagulate suspended particles and therefore he’ll sedimentation to take place

-Aluminium sulfate, Al2(SO4)3

Question 9

What are the 7 stages of water treatment?

Answer 9

1. Screening
2. Flocculation
3. Settlement (sedimentation)
4. Filtration
5. Chlorination
6. Fluoridation
7. pH adjustment

Question 10

Biochemical Oxygen Demand (B.O.D.)

Answer 10

The amount of dissolved oxygen consumed by biological action when a sample of water is kept at 20degrees in the dark for 5 days

Question 11

In B.O.D. why is the sample kept in the dark?

Answer 11

To stop photosynthesis from taking place (this would increase the O2 lvl in the water)

Question 12

Eutrophication

Answer 12

The enrichment of water with nutrients, which leads to an excessive growth of algae and other plants

Question 13

What is the cause of Natural eutrophication?

Answer 13

Caused by the gradual increase in nitrogen & phosphorus lvls caused by sediments building up in lakes

Question 14

What is the cause of Artificial eutrophication?

Answer 14

A sudden increase in nitrate & phosphate nutrients caused by artificial fertilisers being washed into rivers/ domestic sewage from farming

Question 15

Give an example of a heavy metal ion…

Answer 15

Pb2+ (lead ions)

Question 16

How are heavy metal ions removed from water?

Answer 16

Precipitation

E.g, lead ions are reacted with dilute HCL, the lead is precipitated as lead chloride

Question 17

How is the concentration of heavy metal ions in water measured?

Answer 17

Atomic Absorption Spectrometry

Question 18

Primary sewage treatment

Answer 18

A mechanical process where large solids are removed by screening & some suspended solids by settlement (sedimentation)

Question 19

Secondary sewage treatment

Answer 19

A biological oxidation process where the levels of suspended solids and dissolved organic materials are reduced, I.e. the sewage is decomposed by means of bacteria which use the nutrients from the sewage together with oxygen from the air to break down the sewage

Question 20

Tertiary sewage treatment

Answer 20

A process involving the removal of phosphorus compounds by precipitation and nitrogen compounds by biological and
ion-exchange methods

Question 21

Principle of colorimetry

Answer 21

The amount of absorbance of light by a coloured soln. Is proportional to the concentration of the soln.