kuliah 6. inorganic analysis of jkdfbdkjbgjskdibgkjsdbgjksdxgbkdjsgbjdgb

8/13/2019 KULIAH 6. Inorganic Analysis Of jkdfbdkjbgjskdibgkjsdbgjksdxgbkdjsgbjdgb

1/33

inorganic Analysis of

Cation and Anion

Pharmacy, FMIPA - UHAMKA


2/33


3/33

Table 2Analysis of Group I Ions

Step Substance ReagentObservati

onConclusion Precipitate Solution

1 2 mL Solution

Containing Group

I ions

10 drops

6M HC1

White

Precipitate

forms

Ag+, Hg22+

or Pb2+

possible

AgC1,

Hg2C12

PbC12

possible

All other

ions

possible

2 Precipitate from

Step 1

1 mL hot

H2O

Some

Precipitate

Dissolves

All Group

ions

Possible

Pb2+likely

AgC1 and/

or Hg2C12

Pb2+

possible

3 Solution from

Step 2

4 drops1.0 M

K2CrO4

Yellow Ppt

forms

Pb2+

present

PbCrO4 Excess

reagents

4 Ppt from Step 2 10 drops

4 M NH3

Black Ppt

forms

Hg22+

present

Hg and

HgNH2C1

Ag+

Possible

5 So1n from Step 4 6 M HNO3to

make acidic

White

cloudy

ppt

forms

Ag+

present

AgC1 Excess

reagents


4/33


5/33


6/33


7/33


8/33


9/33


10/33


11/33


12/33


13/33


14/33


15/33


16/33


17/33


18/33


19/33


20/33


21/33


22/33

TEST FORTEST METHODOBSERVATIONSTEST CHEMISTRY

Carbonate ion CO32-or hydrogencarbonate HCO3

-

Acid is added to the solid carbonate in a test tube. You could also collect a

sample of gas from a heated carbonate, i.e. the solid is where the liquid is inthe left hand test tube.

Methods of gas preparationare described in more detail on another page.

(i) Add any dilute strong acidto the suspected solid carbonate - if colourlessgas given off, test with limewater.

(ii) Effect of fairly strong heating and testing for any carbon dioxide given off.

Test (ii) will distinguishsodium hydrogencarbonate (NaHCO3readilydecomposes - 'baking powder') from anhydrous sodium carbonate (Na2CO3,thermally very stable).

(i) Fizzing - colourless gaswhich turns limewater milky cloudy(see aboveCO2).

(ii) There might be colour changes in the solid, but you need to collect a sampleof gas from just above the heated solid to see it gives a white precipitate withlimewater.

Apart from hydrated sodium carbonate, sodium hydrogencarbonate is one ofthe few common carbonates to give off water on heating and condenses onside of test tube, but basic carbonates will also give off H2O as well as CO2.
http://www.docbrown.info/page13/ChemicalTests/GasPreparation.htmhttp://www.docbrown.info/page13/ChemicalTests/GasPreparation.htmhttp://www.docbrown.info/page13/ChemicalTests/GasPreparation.htmhttp://www.docbrown.info/page13/ChemicalTests/GasPreparation.htmhttp://www.docbrown.info/page13/ChemicalTests/GasPreparation.htm


23/33

TEST FORTEST METHODOBSERVATIONSTEST CHEMISTRY .

(i) Any carbonate/hydrogencarbonate + acid ==>salt +water + carbon dioxide, then white precipitate withlimewater. The ionic equations are for carbonate ...CO3

2-(s) + 2H+(aq) ==> H2O(l) + CO2(g)

and for hydrogencarbonate ...

2HCO3-(s) + 2H+(aq) ==> H2O(l) + CO2(g)

(ii)The thermal decomposition equations are forcarbonates

MCO3(s) ==>MO(s) + CO2(g)

e.g. M = Mg, Zn, CuO and note some give clear colour

changes in the solid which might be useful to identifythe metal (see heating carbonates in metal cationsection)

and for sodium hydrogencarbonate ...

2NaHCO3(s) ==> Na2CO3(s) + H2O(l) + CO2(g)
http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsc.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsc.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsc.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsc.htm


24/33

Sulphate ion or sulphate(VI) ion SO42-

If the solution also contains the chloride ion, you test withbarium ions 1st, filter off any barium sulphate precipitate and

then test for chloride ion. This is because silver sulphate isalso ~insoluble.

(i) To a solution of the suspected sulfate add dilute hydrochloricand a few drops of barium chloride/ nitrate solution.

(ii) Add lead(II) nitrate solution.

(i) A white precipitate of barium sulfate.

(ii) A white precipitate of lead(II) sulphate.

Test (i) is more definitive.

(i) Ba

2+

(aq) + SO42-

(aq) ==> BaSO4(s)Any soluble barium salt + any soluble sulphate forms a whitedense barium sulphate precipitate.

(ii) Pb2+(aq) + SO42-(aq) ==> PbSO4(s)

Neither white precipitate is soluble in excess hydrochloric

acid.
http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htm


25/33

Sulphite ion or sulphate(IV) ion SO32-

Test (iii) is easily unreliable, the sulphite ion is oxidised byair (dissolved oxygen) to give the sulphate ion, so you will

lucky to obtain a clear solution after adding excess acid.(i) Add dilute hydrochloric acid to the suspected sulfite. Any

sulphite salt + hydrochloric acid ==>chloride salt +sulphur dioxide.

(ii) Test any gas evolved with fresh potassium dichromate(VI)paper. The sulphur dioxide reduces the dichromate(VI) tochromium(III). Note: sulphites do not give ppt. with acidifiedbarium chloride/nitrate because sulphites dissolve in acids.

(iii)Add barium chloride or barium nitrate solution. Ba2+(aq) +SO3

2-(aq) ==> BaSO3(s)

BaSO3(s) + 2HCl(aq) ==>BaCl2(aq) + H2O(l) + SO2(aq)

Character ist ic o f result

(i) Acrid choking sulfur dioxide gas formed.

(ii) The dichromate paper turns from orange to green.

(iii)A white ppt. of barium sulphite which dissolves in excess

hydrochloric acid to give a clear colourless solution.


26/33

Sulphide ion S2-

In test (ii) dangerous hydrogen sulphide is formed.

(i) If soluble, add a few drops lead(II) ethanoate solution.Pb2+(aq) + S2-(aq) => PbS(s)

(ii) If solid, add dil. HCl(aq) acid, test smelly gas withdamp lead(II) ethanoate paper (old name leadacetate).

MS(s) + 2H+(aq) => M2+(aq) + H2S(g)(e.g. M = Pb, Fe, Cu, Ni etc.) Then reaction (i) aboveoccurs on the lead(II) ethanoate paper (old name leadacetate).

Character ist ic o f resul t

(i) Black ppt. of lead sulphide.(ii) Rotten egg smell of hydrogen sulphide and the H2S

gas turns lead(II) ethanoate paper black.

Chl id i (Cl )


27/33

Chloride ion (Cl-)If the solution also contains the sulphate ion, you test withbarium ions 1st, filter off any barium sulphate precipitate andthen test for chloride ion. This is because silver sulphate is

also ~insoluble, so the two precipitates of silver sulfate andsilver chloride could not be distinguished

(i) If the chloride is soluble, add dilute nitric acid and silver nitratesolution.

Ag+(aq) + Cl-(aq) ==> AgCl(s) Any soluble silver salt + anysoluble chloride gives a white silver chloride precipitate, that

darkens in light(ii) If insoluble salt, add conc. sulphuric acid, warm if necessarythen test gas as for HCl.

Cl-(s) + H2SO4(l) ==> HSO4-(s) + HCl(g) ,

then Ag+(aq) + Cl-(aq) ==> AgCl(s)

(iii) Add lead(II) nitrate solution. Not a very specific test - test (i) is

best. Pb2+(aq) + 2Cl-(aq) ==> PbCl2(s)Characterist ic of resu lt

(i) white precipitate of silver chloride soluble in dilute ammonia.

(ii) You get nasty fumes of hydrogen chloride which turn bluelitmus red and give a white precipitate with silver nitratesolution.

(iii) A white ppt. of lead(II) chloride is formed.
http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htm


28/33

Bromide ion (Br-)(i) If bromide soluble, add dilute nitric acid and silver nitrate

solution. Ag+(aq) + Br-(aq) ==> AgBr(s)

Any soluble silver salt + any soluble bromide gives a creamsilver bromide precipitate

(ii) If insoluble salt, add conc. sulphuric acid, warm if necessary.

The bromide ion is oxidised to bromine and the sulphuric acidis reduced to sulphur dioxide.

(iii) Add lead(II) nitrate solution. Not a very specific test - test (i) isbest. Pb2+(aq) + 2Br-(aq) ==> PbBr2(s)

Character ist ic o f result(i) Cream precipitate of silver bromide, only soluble in

concentrated ammonia.(ii) Orange vapour of bromine and pungent fumes of SO2, test forsulphur dioxide.

(iii) A white ppt. of lead(II) bromide is formed.
http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htm


29/33

Iodide ion (I-)(i) If iodide soluble, add dilute nitric acid and silver nitrate

solution.

Ag+

(aq) + I-

(aq) ==> AgI(s) , any soluble silver salt + anysoluble iodide ==> silver iodide precipitate,

(ii) If insoluble salt can heat with conc. sulphuric acid, (ii) getpurple fumes of iodine and very smelly hydrogen sulphide,(iii) if soluble, add lead(II) nitrate solution.

iodide ion is oxidised to iodine and the sulphuric acid is

reduced to 'rotten eggs'smelly hydrogen sulphide,(iii) If iodide soluble, add lead(II) nitrate solution.

insoluble lead(II) iodide formed

Pb2+(aq) + 2I-(aq) ==> PbI2(s)

Character ist ic o f result(i) Yellow precipitate of silver iodide insoluble in concentrated

ammonia.

(ii) purple vapour and rotten egg smell!, (iii) a yellow precipitateforms

(i) Yellow precipitate of lead(II) iodide. Not too definitive -Test (i)

best.


30/33

Nitrate ion or nitrate(V) ion NO3-(i) Boil the suspected nitrate with sodium hydroxide solution and fine aluminium

powder (Devarda's Alloy) or aluminium foil. The aluminium powder is apowerful reducing agent and converts the nitrate ion, NO

3

-, into ammonia gas,NH3

(ii) Add iron(ii) sulphate solution and then conc. sulphuric acid (the 'brown ring'test). NO complex of iron(II) formed

(iii) Strongly heating nitrates of M2+salts. a general thermal decompositionequation for this reaction is

2M(NO3)2(s) ==> 2MO(s) + 4NO2(g) + O2(g), where M = Pb, Zn, Mg, Cu etc.

Character ist ic of result

(i) the fumes contain ammonia, which turns red litmus blue, see ammonia testdetails

(ii) Where the liquids meet a brown ring forms

(iii) Nasty brown gas (beware!) of nitrogen (IV) oxide(nitrogen dioxide)

Nitrite ion or nitrate(III) ion NO2-No simple test to clearly i.d. it,

(i) in acid solution it decomposes to give colourless NO gas which rapidlyoxidises to nasty brown fumes of NO2,

(ii) it decolourises (purple ==> colourless) acidified potassium manganate(VII),

(iii) it liberates iodine from acidified potassium iodide solution,

(iv) forms ammonia with hot Al powder-foil/NaOH(aq) (see nitrate test) and gives

'brown ring' test - see nitrate testsabove. Ammonium ion
http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsa.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htmhttp://www.docbrown.info/page13/ChemicalTests/ChemicalTestsg.htm


31/33

Ammonium ion(NH4+)

If no smell at first, add COLD sodium hydroxide solution to thesuspected ammonium salt and test any gas with red litmus.

Smelly ammonia released! and red litmus turns blue. Ammoniagas is evolved:

NH4+(aq) + OH-(aq) ==> NH3(g) + H2O(l)

Acids Hydrogen ion i.e. H+or H3O+ion(note: to completely

identify acids you need to test for the anion e.g. chloride for HCletc.)

(i) Litmus or universal indicator or pH meter.

A pH meter reading gives a value of less than 7, the lower thepH number the stronger the acid, the higher the H+ concentration,

(ii)Add a little sodium hydrogencarbonate powder.

HCO3

- (aq) + H+(aq) ==> H2

O(l) +CO2

(g)

Character ist ic of resu lt

(i)Litmus turns red, variety of colours with univ. ind. strong - red,weak - yellow /orange, depending on strength of acid.

(ii)Fizzing with any carbonate - test for CO2as above.


32/33

Ammonium ion(NH4+)..

Alkali: Hydroxide ion i.e. a soluble base (alkali) which forms theOH- ion in water (note: to completely identify alkalis you need

to test for the cation e.g. sodium for NaOH etc.)(i) Litmus or universal indicator or pH meter.

A pH meter gives a value of more than 7, the higher the pHnumber the stronger the alkali, the higher the OH-concentration, (ii) ammonia gas is evolved:

(ii) Add a little of an ammonium salt. Ammonia released from thesalt.NH4+(aq) + OH-(aq) ==> NH3(g) + H2O(l)

Character ist ic o f resul t(i) It turns litmus blue, variety of colours univ. ind. dark green -

violet for weak - strong.

(ii) If strongly alkaline ammonia should be released, see ammoniatestfor rest of details


33/33

Chromate(VI) ion (CrO42-)/(yellow)

These tests are not very definitive, but collectively theyare a good 'pointer'!

(i) Add dilute sulphuric acid.

CrO42-(aq) + 2H+(aq) ==> Cr2O72-(aq)

(ii) Add barium chloride/nitrate solution.

Ba2+(aq) + CrO42-(aq) ==> BaCrO4(s)

(iii)Add lead(II) nitrate solution.Pb2+(aq) + CrO42-(aq) ==> PbCrO4(s)

Character ist ic o f result

(i) The yellow solution turns orange as the dichromate(VI)ion is formed.

(ii) A yellow precipitate of barium chromate(VI) is formed.

(iii) A yellow precipitate of lead(II) chromate(VI) is formed.'lead chromate'

kuliah 6. inorganic analysis of jkdfbdkjbgjskdibgkjsdbgjksdxgbkdjsgbjdgb

Documents