water

Question 1

Defien hard water

Answer 1

water that will not form a lather easily with soap. Caused by the presence of CA2+ AND Mg 2+ ions

Question 2

what ions cause hard water

Answer 2

ca2+ and mg2+

Question 3

what is the most common substance found in soap

Answer 3

sodium stearate

Question 4

how does soap react with hard water

Answer 4

sodium stearate in soap will react with the ca2+ or mg2+ ions in the hard water to form a grey insoluble scum called calcium stearate
A lather will only form when all calcium ions in the water have reacted to form calcium stearate

Question 5

how do you test in the lab for the presence of hard water

Answer 5

add water to test tube and add soap
Shake
If it is hard a lather will not form a scum will form instead
If it is soft a lather will form easily

Question 6

what are the advantages of hard water

Answer 6

Tastes nicer
Good for brewing industry
Provides calcium for healthy teeth and bones

Question 7

what are the disadvantages of hard water

Answer 7

Wastes soap
Produces a scum
Blocks pipes, and causes limescale in kettles

Question 8

What is temporary hardness

Answer 8

Hardness that can be removed by boiling
Caused by calcum hydrogencarbonate

Question 9

where does temporary hardness come from

Answer 9

rain water is slightly acidic due to the co2 that it gets when it falls through the atmosphere and this forms a weak carbonic acid. This then reacts with limestone and forms the calcium hydrogen carbonate that causes temporary hardness

Question 10

how can you remove temporary hardness

Answer 10

boiling as it removes the ca2+ ions

Question 11

define permanent hardness

Answer 11

hardness that cannot be removed by boiling
Caused by calcium or magnesium sulphate

Question 12

what is distilled water

Answer 12

water mixture is heated and water evaporates as it has a lower boiling point than the other dissolved solids in it. Water vapour is then condensed to form pure water. This removed all suspended solids, dissolved soilds and gases so is the prest form of water

Question 13

what is deionised water

Answer 13

tap water is passed through a mixed bed of resin and positive and negative ions are removed. Usually it still contains dissolved gases but no ions

Question 14

explain how does adding soap remove hardness

Answer 14

add soap to a smaple of wter and shake. The calcium ions in the water should combine with the sodium stearate in the soap to form a scum. Keep adding soap until a lather forms now you will know that all ca2+/mg2+ ions have been removed

Question 15

explain how distillation removes water hardness

Answer 15

you separate substances accoridng to their boilign points
water has a very low boiling point than the substances that causes water hardness ca/mg2+ so b boilign water can be evaporated and then condensed to form pure water. But it is expensive

Question 16

how does washing soda remove water hardness

Answer 16

washing soda is hydrated sodium carbonate
the carbonate ion in the washing soda react with the calcium ions in the water forming calcium carbonate thus removes calcium ions from water

Question 17

how does ion exchnage in the household work to remove water hardness

Answer 17

with cation exchange resin
water containing ca/mg 2+ ions are passed through the cation resin and are replaced with NA2+ ions which don’t cause water hardness

Question 18

how do u remove water hardness in the lab with ion exchnage

Answer 18

use a mixed bed of resin
it will remove all ions

water containing all ions including ca/mg is passed through mixed resin contain anion and cation

cation exchange removed the ca2+ and mg2= ions and releases H+ ions
anion exchange takes out things like cl- and replaces them with OH- ions

Question 19

what are the 7 steps of water treatment

Answer 19

screening
flocculation
sedimentation
filtration
chlorination
fluoridation
ph adjustment

Question 20

what happens in the screening stage of water treatment

Answer 20

water from a river or lake is passed through a wire mesh and this removes large pieces of floating debris

Question 21

what happens in the sflocculation stage of water treatment

Answer 21

is the coagulation if small floating particles in water to from larger particles.
Aluminium sulphate is added to help particles bind together to allow sedimentation to occur.
Issues- aluminium sulphate corrodes pipes and affects taste

Question 22

what happens in the sedimenation stage of water treatment

Answer 22

water passes into sedimentation tanks and it flows in from the bottom of the tank slowly to allow max settlement. Clear water overflow into channels
90% Of suspended particles are removed

Question 23

what happens in the filtration stage of water treatment

Answer 23

water from sedimentation tanks is passed through a bed of sand to remove any remaining suspended solids

Question 24

what happens in the chlorination stage of water treatment

Answer 24

water has chlorine added in the form of chlorine gas to kill bacteria and make water safe to drink. But it affects the waters taste and smell

Question 25

what happens in the screening stage of water treatment

Answer 25

1 ppm of fluoride compounds- sodium fluoride are added to water to strengthen the enamel. But too much can stain teeth

Question 26

what happens in the ph adjustment stage of water treatment

Answer 26

optimum ph is 7.2 if water is too alkali sulphuric acid is added to lower ph but it can corrode pipe if too much used if water is too acidic calcium hydroxide is added to increase the ph but it affects the taste

Question 27

define BOD- Biological oxygen demand

Answer 27

the amount o dissolved oxygen n ppm consumed by biological action when a sample of water is stored at 20 degrees c and in the dark for 5 days

Question 28

what is bod a test for

Answer 28

the amount of dissolved o2 in water

Question 29

how does temp affect the solubility of 02 in water

Answer 29

as you increase the temp the solubility of 02 decreases At higher temperatures, the bonds or interactions between water molecules and gas molecules (like O₂) become weaker. Water can't “hold on” to the oxygen as well, so oxygen escapes into the atmosphere. It is also a non polar molecule 02

Question 30

what can dissolved o2 levels be affected by

Answer 30

photosynthesis respiration

Question 31

how do you ensure there is enough dissolved 02 left in the sample after 5 days

Answer 31

it is diluted using a fixed amount of water

Question 32

how do you carry out a BOD test

Answer 32

fill to water bottles to the top with water to be tested use winkler method to measure the bod of one water bottle immeidatlety incubate the other in the dark at 20 degrees for 5 days the difference between the initial and the final conc meausred in mg/l or ppm is the bod

Question 33

what precautions should you take when carrying out bod test

Answer 33

fill the bottle by hoding it completely under water to prevent ait getting in put the lid on the bottle below the surface immediaelty place 2nd bottle in a dark room to prevent photsynthesis

Question 34

what does a high bod value mean

Answer 34

lotsof organic material presnet so more o2 s rmeoved from water

Question 35

what is eutrophication

Answer 35

it is the enrichment of water with nutrients which can lead to excessive growth of algae and othe rplants

Question 36

what is natural eutrophication

Answer 36

occurs in lakes and is caused by nitrogen and phosphates gradually increasing over time and sediment build sup

Question 37

what is artifical eutrophication

Answer 37

it is caused suddenly eg by fertisers running of the land and into lakes

Question 38

why does eutropjcation cause rapid growth

Answer 38

plants absorb the nitrates and phosphates which causes plants and alage to rapidly grow

Question 39

descibe how the bod chnages in a lake over time

Answer 39

initially bod will increase as algae undergo photosynthesis and produce 02. However, they don't live long so are broken down by microorganisms and this uses up more 02 and thus decreases o2 conc killing fish. Net decrease in 02

Question 40

how are heavy metals removed from water

Answer 40

precipitation reactions

Question 41

name some heavy metals

Answer 41

lead, cadmium, mercury

Question 42

where do heavy metals come from

Answer 42

discharge from factories batteries not disposed of correclty old houses had lead pipes

Question 43

why is mercury dangerous

Answer 43

it is poisonous it is dangerous when inhaled and less dnagerous when swollowed can lead to birth defects and death

Question 44

why are heavy metals called hevay metals

Answer 44

they have a high relative atomic mass

Question 45

how do you rmeove lead ions by precipitation reaction?

Answer 45

react them with hcl and lead chloride is precipitated or react them with calcium hydroxide to form lead hydroxide

Question 46

how do you remove mercury ions from water

Answer 46

react it with sodium sulphide to form mercury sulphide

Question 47

what is a cumilative posion in reation to hevay metals

Answer 47

hey build up in the body over time

Question 48

why must sewage be treated before releasing to lake etc

Answer 48

to minimise bod

Question 49

what is the primary treatment for sewage

Answer 49

. it is a mechnaical process in which large solids are removed by screening and some suspened solids are rmeoved by sedimentation

Question 50

what is the primary treatment for sewage

Question 51

what is the primary treatment for sewage

Question 52

What is the compound in manner hard water

Answer 52

Calcium sulphate

Question 53

What is the compound in temporary hard water

Answer 53

Calcium hydrogencarbonate