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Qualitative analysis test

To detect one cation and one anion from the

following:


(Insoluble salts to be excluded)

Apparatus:

Micro test-tubes with stand, test tube holder, kerosene burner,

W-tube, well plate, dispensing bottles, china dish, cotton swabs,

charcoal cavity, W. Tube etc.

Chemicals:

6MH2

SO4, 6MHCl, lime water, sodium carbonate, sodium metal, BaCl2

solution, KMnO4

solution, KI solution, starch solution, acetic acid

Introduction:

The inorganic qualitative analysis involves the identification of ions

present in a sample. The salt consists of anion and cation. The basis

of identification is the observed chemical behaviour of the

components. The salt analysis may be systematically carried out in

the following three steps:

i) Preliminary examination

ii) Detection of anions and

iii) Detection of cations

Preliminary examination:

First we proceed to examine the physical properties of the salt. This

is followed by the action of heat on the salts and also certain tests,

such as flame test etc.

Detection of Anions:

A preliminary hint about some anions may be obtained by the formation

of volatile or gaseous products when the salt is treated with



i) dil.H2SO4 (for CO3 2-, S2-, SO3 2-, N02 - and CH3COO-) ii) conc.H2SO4 (for C1- , Br-, I- and NO3 - ) 1. Take about 10 mg of the salt in a dry test tube with the help of a spatula. 2. Heat the test tube over the burner and observe the change. Note the colour and odour of the gases if evolved as given in Table 2. Table 2 : Action of Heat Observation Inference Chemistry Involved Ammonia gas evolves NH4 + (NH4) 2 CO3 →NH3+CO2+H2O Carbon dioxide evolves CO3 2– present CaCO3 → CaO + CO2 Sulphur dioxide evolves SO4 2- may be 2FeSO4 → Fe2O3+ SO2 + SO3 present Nitrogen dioxide evolves NO3 – 2Cu(NO3)2 →2CuO + 4NO2 +O2 Colour of the salt on heating changes from 1. Some salts change their Cu2+ salt By losing water of colour blue to white crystallization 2. Green to yellow Ni2+ salt 3. White (when cold) to Zn2+ salt yellow (when hot) Flame Test Prepare a paste of small amount of the salt with one or two drops of conc.HCl on a watch glass. Take the paste on the loop of Nichrome wire or cotton swab, put it in the burner’s flame and observe the colour.

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