1 Qualitative Analysis of Inorganic Compounds

Qualitative analysis of inorganic compounds

The experiments are written for experienced science teaching staff to use as instructions for a

supervised class of students. The experiments are not designed for students or inexperienced

members of the public to perform without supervision. If you wish to attempt the experiments,

ensure that you have completed a legally adequate risk assessment beforehand and that you

work within the constraints of the risk assessment.

Test Observation Inference

X(s) + dilute acid

solid dissolves - effervescence

occurs - a colourless gas given

off that turns limewater milky.

CO2 given off. X contains carbonate ions

CO32-.

solid dissolves - effervescence -

a pungent colourless gas that

turns acidified dichromate

green.

SO2 given off. X contains sulphite ions

SO32-

solid dissolves - effervescence

occurs - a colourless gas given

off that gives characteristic pop

with a lighted splint.

H2(g) given off. X is a metal. X could be

aluminium , zinc, iron, tin or magnesium

X(aq) + sodium

hydroxide white ppt. - soluble in excess.

aluminium hydroxide, Al(OH)3; lead (II)

hydroxide, Pb(OH)2; or zinc hydroxide,

Zn(OH)2, formed. X contains one of the

following: aluminium ions, Al3+; lead (II)

ions, Pb2+; zinc ions, Zn2+.

reddish brown ppt. - insoluble in

excess.

Iron (III) hydroxide, Fe(OH)3 formed. X

contains iron (III) ions, Fe3+.

dirty green ppt. - insoluble in

excess. Slowly turns reddish

brown where exposed to air.

iron (II) hydroxide, Fe(OH)2 formed. X

contains iron (II) ions, Fe2+.

blue ppt. - insoluble in excess.

copper (II) hydroxide Cu(OH)2 formed. X

contains Copper (II) ions Cu2+.

light brown ppt. - darkens on

standing.

manganese (II) hydroxide formed.

Mn(OH)2. X contains manganese (II) ions

Mn2+

X(s) + sodium

hydroxide .Warm

Pungent colourless gas given

off - turns moist red litmus blue.

White fumes formed with conc.

HCl

The gas is ammonia NH3. X(s) contains

ammonium ions NH4+

2 Qualitative Analysis of Inorganic Compounds

X(aq) + aqueous

ammonia

(ammonium

hydroxide)

white ppt. - insoluble in excess. aluminium hydroxide Al(OH)3 or Pb(OH)2. X

contains Al3+ or Pb2+

white ppt. - soluble in excess.

Zinc hydroxide Zn(OH)2 formed. X contains

Zn2+.

reddish brown ppt. - insoluble in

excess

Iron (III) hydroxide formed; Fe(OH)3. X

contains iron (III) ions, Fe3+

dirty green ppt. - insoluble in

excess. Slowly turns reddish

brown where exposed to air.

Iron (II) hydroxide, Fe(OH)2 formed. X

contains iron (II) ions, Fe2+

blue ppt. - dissolves in excess

to form a deep blue solution.

copper (II) hydroxide Cu(OH)2. complex ion

formed. X contains Cu2+.

no ppt. formed but the solution

becomes a different colour.

transition metal complex ion formed. X

contains a transition metal ion.

X(aq) + barium

chloride (or

nitrate).

white ppt. - insoluble in excess. barium sulphate formed. BaSO4. X contains

sulphate ions SO42-.

X(aq) + chlorine

solution

yellow or reddish brown

colouration Bromine Br2 or iodine I2 formed

turns tetrachloromethane

purple. Iodine I2 formed. X contains iodide ions I-

turns tetrachloromethane

orange or yellow

bromine Br2 formed. X contains Bromide

ions Br-

X(aq) + lead

nitrate or lead

ethanoate

bright yellow ppt. - insoluble in

excess

lead (II) iodide, PbI2; or lead (II) chromate,

PbCrO4, formed. X contains iodide ions I- or

chromate ions CrO42-

White ppt. - insoluble hot water.

lead (II) carbonate PbCO3 formed. X

contains carbonate ions, CO32-.

White ppt. - soluble in hot water

lead (II) chloride, PbCl2, or lead (II)

bromide, PbBr2, formed. X contains

chloride ions, Cl-, or bromide ions, Br-.

X(aq) + lead (II)

nitrate or lead (II)

ethanoate

yellow ppt. - soluble in excess. lead (II) iodide, PbI2, formed. X contains

iodide ions I-.

X(aq) +

potassium iodide yellow ppt. - soluble in excess.

lead (II) iodide, PbI2, formed. X contains

lead (II) ions Pb2+.

Yellow or reddish brown

colouration produced.

Iodine I2 formed. X is an oxidising agent.

3 Qualitative Analysis of Inorganic Compounds

X(aq) +

potassium

manganate (VII)

solution

(acidified)

purple colouration fades.

permanganate has been

reduced.Mn2+ formed. X is a reducing

agent.

X(aq) +

potassium

dichromate (VI)

solution

(acidified)

orange solution becomes green

or blue/green.

dichromate has been reduced. Cr3+ formed.

X is a reducing agent.

X(aq) acidifed

with nitric acid

then silver nitrate

added.

white ppt. - darkens in bright

daylight - soluble in excess dil.

ammonia.

silver chloride, AgCl, formed. X contains

chloride ions Cl-.

off white creamy ppt. - soluble

in excess conc. ammonia.

silver bromide, AgBr, formed. X contains

bromide ions Br-.

X(aq) + silver

nitrate

pale yellow ppt. - insoluble in

dil. and conc. ammonia.

silver iodide, AgI, formed. X contains iodide

ions I-.

X(aq) + sodium

carbonate

solution.

white ppt. - insoluble in excess.

insoluble carbonate formed. X contains

ONE of the following: magnesium ions,

Mg2+; calcium ions, Ca2+; strontium ions,

Sr2+; barium ions, Ba2+; zinc ions, Zn2+; lead

(II) ions, Pb2+.

dirty green ppt.

copper (II) carbonate, CuCO3 formed. X

contains copper (II) ions, Cu2+.

effervescence - colourless gas

which turns lime water milky.

carbon dioxide formed. X is acidic

(produces H+ ions in solution).

X(aq) + sodium

hydroxide +

aluminium and

warm

Pungent colourless gas given

off - turns moist red litmus blue.

White fumes formed with conc.

HCl

The gas is ammonia NH3. X(aq) contains

nitrate ions NO3-

X(aq) + dil.

sulphuric acid

effervescence - colourless gas -

turns lime water milky.

carbon dioxide formed. X contains

carbonate ions CO32-.

white ppt. formed - insoluble in

excess

insoluble sulphate formed. X contains ONE

of the following : calcium ions Ca2+ barium

ions Ba2+ strontium ions Sr2+ lead (II) ions

Pb2+

X(s) + conc.

sulphuric acid.

effervescence - misty white

fumes which turn moist blue

litmus red.

hydrogen chloride HCl given off. X contains

chloride ions Cl-.

4 Qualitative Analysis of Inorganic Compounds

effervescence - misty white

fumes + orange fumes - blue

litmus bleached.

hydrogen bromide HBr and bromine

Br2 formed. X contains bromide ions Br-.

effervescence - purple black

fumes formed. iodine I2 formed. X contains iodide ions I-

X(s) + conc.

hydrochloric acid

Pungent green-yellow gas given

off, bleaches litmus paper white.

Chlorine gas Cl2 given off. Solid is an

oxidising agent. Red solid could be

Pb3O4 Brown solid could be lead (IV) oxide.

Black solid could be manganese (IV) oxide

MnO2

effervescence, colourless gas

given, gives a characteristic pop

with a lighted splint

hydrogen gas formed H2. X could be

aluminium, magnesium , zinc, iron or tin.

X (aq) + conc.

Hydrochloric acid

White ppt. formed soluble in

excess acid

Lead (II) chloride formed. Forms a complex

ion PbCl4- with excess conc. hydrochloric

acid

5 Qualitative Analysis of Inorganic Compounds

Flame tests

A small amount of the unknown substance is added to a quiet blue Bunsen flame. A wire loop,

cleaned and moistened with concentrated hydrochloric acid, is used for this purpose. Some

metals will colour the flame:

(crimson) Lithium (yellow/orange)Sodium (lilac)Potassium

(green/blue)Copper

(orange/red)Calcium (red) Strontium

(apple

green) Barium

(white/blue) Lead

6 Qualitative Analysis of Inorganic Compounds

References

Davies, DG & Kelly, TVG Inorganic Reactions at Advanced Level published by Mills &

Boon ISBN 0 263 05692 9