Water and Colours

Question 1

Making portable water from fresh water
3 processes and what they do

Answer 1

FILTRATION - removes insoluble solids like stones, leaves, soil.
Water is passed through sand and gravel beds , can be cleaned by forcing water back up through them
SEDIMENTATION- causes the tiny suspended particles to stick together into clumps which settle out.
Aluminium sulfate is a coagulant (added to make the particles clump together to form larger particles)
Mixture is filtered again through fine carbon to remove these large particles
CHLORATION- kills microbes.
Chlorine is bubbled through in water to kill microbes , which sterilises the water

Question 2

Making potable water from seawater
Desalination
Carried out by what
Disadvantage

Answer 2

Process of removing substances from seawater

Distillation- water evaporates leaving salt behind and steam is then condensed

It’s expensive to produced so is usually reserved for warm countries with lots of solar energy

Question 3

Physical test
Physical properties
Methods

Answer 3

Colourless liquid with a melting point of 0oc and boiling point of 100oc

Measure its boiling point, pure water boils at 100oc, but if boiling point increases impurities are present

Evaporating it (to dryness), pure water will leave no solids behind in dish when evaporated , impure will leave solids behind in dish

Question 4

Chemical test for water
Method
Result and observations
Water of crystallisation equation
Reversible

Answer 4

Add a few drops of water to a spatula of anhydrous copper(ll) sulfate in a test tube

White powder turns blue
Mixture gets very warm

CuSo4 + 5H2O-> CuSO4.5H2O

Heat to remove water

Question 5

Flame test

Answer 5

Dip nitrichrome wire in conc. HCl and hold in buses
Dip wire into conc.HCl and them sample
Hold at edge of blue busen flame
Observe and record colour

Question 6

Observations
Little crying seals obide politely like cool bananas cool groovy bananas
Lithium

Answer 6

Crimson

Question 7

Sodium

Answer 7

Orange

Question 8

Potassium

Answer 8

Lilac

Question 9

Calcium

Answer 9

Brick red

Question 10

Copper

Answer 10

Green-blue

Question 11

Identifying metal cations using sodium hydroxide and ammonia solution
Why ammonia solution

Answer 11

Is an alkali, so make hydroxide ions when dissolved in water, this is why the equation for the two precipitation reactions is the same

Question 12

Identifying metal cation
Method

Answer 12

Dissolve a small sample of the salt in deionised water
Place approx 3cm3 of the solution in test tube
Add NaOH/NH3 solution drop by drop until it is in excess (test tube about 2/3 full)
Stopper and shake the test tube
Record colour of any precipitates and observe if they dissolve when excess solution was added

Question 13

Zam precipitate colour
Zn 2+
Al 3+
Mg 2+

Answer 13

White
In excess:
Dissolved in both
Dissolved in NaOH sol remained in NH3 sol
Ppt remained in both

Question 14

All in NaOH solution in excess
Colour, in NH3 solution
Fe2+
Fe3+
Cu2+

Answer 14

Ppt remains
Green ppt , ppt remains
Rust ppt , ppt remains
Blue ppt , dissolves forming dark blue solution

Question 15

Identifying anions
Anions test
Ionic equation

Answer 15

Make a solution of the solid salt in deionised water
Add a few drops of nitric acid followed by a small amount of silver nitrate solution

Ag+ (aq) + X- (aq) ->AgX(s)

Question 16

Precipitates of
Chloride
Bromide
Iodide

Answer 16

White ppt
Cream ppt
Yellow ppt

Question 17

Sulfate test
Method
Result

Answer 17

Make a solution of solid salt in deionised water
Add a few drops hydrochloric acid followed by a small amount of barium chloride solution

White ppt

Question 18

What colour of precipitate and solution is sulfate ions in copper sulfate

Ionic equation

Answer 18

White ppt in blue solution

Ba2+(aq) + SO42-(aq) -> BaSO4 (s)

Question 19

Lime water name

Answer 19

Calcium hydroxide