Colours And Tests

Question 1

Carbonate ion test

How to don+ confirm

Answer 1

1) nitric acid
- effervescence
- collect gas bubble through lime water (ca(OH)2 )
If co2 then jt will form a white precipitate of calcium carbonate , therefore if co2 released it was a carbonate

Question 2

Sulfste test

Answer 2

Barium NITRATE to solution
- if sulphate ion present, white precipitate Ba(So4) forms

(Don’t use barium chloride if need to do halide test after)

Question 3

Halide tests

Colours + HOW TO DIFFERENTIATE IF COLOURS ARE SIMILAR (easy way to remember the concs)

Answer 3

Silver nitrate
- based on colour of prefipate milk cream butter (white cream yellow) is the halide
- to confirm , dissolve in ammonias

• first dissolved in conc and weak
• second dissolved in comc only
• 3rd doesn’t dissolve at all (conc )

Easy way to remember is solubility increase group 2 so decrease group 7.)

Question 4

Sequence of tests

Why pretty much

Answer 4

1) carbonate first
- only carbonates release co2 so can safely rule out,
- baroum CARBONATE IS A WHITE PRECIPITATE

2) sulfste test 2nd
- SILVER SULFSTE + AND SILVER CARBONATE FORM PRECIPITATED TOO

4) therefore must do halide last

Question 5

What acid and solution to use and why (sulfruic nitric what?)

Answer 5

Nitric acid, barium nitrate , silver nitrate, so that you don’t introduce RSNDOM sulfste , chlorine ions if doing series of tests

Question 6

How ti do tests to identify mixture of compounds ? For thr csbrknste sulfste halide

Answer 6

1) add nitric acid till stop bubbling, now you know all carbonate reacted
2) add excess barium nitrate, any barium sulfste precipitate out, filter
3) do halide test, with ammonia to check

Don’t use sulfruic or hydrochloric acid etc

Question 7

Ammonium ion cation test

WHAT REAGENT NEEDED
what way to confirm

Answer 7

REACT NAOH with ammonium soltuoj

Heat up
Ti confirm , add DAMP litmus paper red near neck, should turn blue

Question 8

AS tests summary
4 tests + required order and why

Answer 8

1) carbonate = nitric acid = effervescence = collect + bubble in like water (Ca(OH2) ) and should form white calcium carbonate precipitate
2) sulfste = barium nitrate = white precipitate barium sulfate
3) halide = silver nitrate = milk cream butte , add conc / dilute (decrease solubility lower you go) to differentiate
4) am,onium = NaOH to solution, heat, use red litmus paper becomes blue

Must do carbonate sulfste then silver, as barium carbinste , silver carbonate and silver sulfste all are precipated (white)

Question 9

Condition for sodium hydroxide in disprortijstion with chlorine

Answer 9

Cold and dilute

Question 10

Fe 2+ fe 3+ when in solution colour

Answer 10

Pale green fe 2+
Yellow fe 3+

Question 11

Cr 6+ cr 3 + colour in solution

How to remember easily

Answer 11

We now acidified potassium dichromate is an oxidising agent. Therefore, the chromium must be REDUCED

=cr6+ is orange
Cr 3+ is GREEN

Question 12

Hexa aqua copper basic colour

How is it formed

Answer 12

PALE BLUE

Formed when copper sulfste dissolved in water

Question 13

1) hexa aqua copper resctions with ammonia!

All 3 colour changed

Answer 13

Drop by drop,
- initially will get Cu(OH)2 precipitate blue formed
- then dissolved in ammonia to give Copper 4 ammonia 2 water DARK BLUE

Question 14

2) hexa aqua copper resvtion with chlorine ions

What is intial and final colour
- what happens if you add water back to new complex ion ?

• why is there a green colour seen if slowly add chlorine ?

Answer 14

• as chlorine ions are big, remember only 4 can react
• this forms [cu (cl4)] -2 which is YELLOW

2) adding back with water reverses and makes it yellow to pale blue again

3) a green intermediate is formed as adding chlorine ions as the yellow and pale blue mix, don’t fret

S

Question 15

3) what is chromium hexa water colour base

Answer 15

This is violet

Question 16

3) chromium hexa water resvtion with ammonia dropwise

All 3 collour changes

Answer 16

• intially precipitate formed = Cr (Oh)3 which is GREY GREEN
  RRECIPITATE
• then dissolved in excess ammonia to form CHROMIUM HEXA 6 AMMONIA

Which is VIOLET

Question 17

What is the source for chlorine ions for 2)

Answer 17

Concentrated HYDROCHLROIC ACID

Question 18

Precipitation
1) Cu2+

Answer 18

Blue to blue precipated (Cu (Oh)2

Question 19

Precipitation
2) Fe 2+
What else

Answer 19

Pale green to green (Fe(Oh)2

Then in air oxidise to Fe 3+ thus Fe (OH) and BROWM

Question 20

Preiciaptiom

Fe3+

Answer 20

Fe 3+ is yellow and becomes orange brown precipated fe (Oh)3 as seen before

Question 21

Rediaptiom 4)

Mn 2+

Answer 21

Mn 2+ pale pink and become light brown in Mn(OH)2 precisiptr

Question 22

5) precipitation
Cr 3+

Special case unlike other 4 REMEMBER

Answer 22

Cr 3+ is VIOLET
Becomes Cr(OH)3 green grey precipated (as seen before)

BUT DISSOLVED IN EXCESS NAOH

Giving [Cr (OH)6] -3 which is DARK GREEN

Question 23

Remember these all REACT and form same precipated with ammonia and NaOH except

Answer 23

They all do, and all use same equations so don’t get confused

• however Cr 3+ does make the precipated but doesn’t dissolve in excess ammonia to form thr Comolex hexa h dry oxide Cromium dark hreen

Question 24

All colours ligand + precipitation

Answer 24

Ligand
1) hexa aqua copper (light blue) with ammonia = precipated Cu (Oh)2 blue = dissolved in excess to 4 ammonia 2 water copper (dark blue) complex ion
2) hexa aqua copper (light blue) with hcl = cu cl4 2- (yellow). Reversible + green intermediate can be formed as colours mix
3) hexa aqua chromium is Violet . Add ammonia = cr(Oh)3 green grey preicpste = dissolved in excess to form hexa ammonia chromium purple,

Preiciaptiom
1) Cu2+ blue to blue preicpste
2) fe 2+ light green to green , to orange brown as oxidises to Fe3+ I’m air
3) fe3+ yellow to orange brown like ^
4) mn 2+ pale pink to light brown

5) cr3+ Violet becomes cr (oh)3 green Grey precipated as seen before = cr (Oh)6 -3 compex dark green

All react the same with ammonia, except when cro (Oh)3 excess ammonia forms cr 6 ammonia no cr 6 hydroide …

Z

Question 25

Extra resvtion and colours

Copper iodine

Need to know

Answer 25

2 Cu 2 + + 4I- —> 2CuI + I2

Copper iodine is a white precipated , iodine is a brown colour

Question 26

What colour is pure copper (s) which is achieved in disprotiinstikn resvtion
And cu (so4)

Answer 26

Cu (s) brown
Cu(so4) is blue

Question 27

Colour of sulfur

Answer 27

Like orange

Question 28

Colours of hexa aqua Fe 2+ and Fe3+, for anything?

Answer 28

Just like how cu2+ hexa aqua is blue too (although light ) they take rhe SAME COLOUR Z

THUS light green and orange brown