Question

Identify one cation and one anion in the given unknown salt M1 by performing dry test

Answer 1

Identify one cation and one anion in the given unknown salt M1 by performing the dry heat test.

• This test is done by warming a small quantity of salt in a dry test tube.

• On heating, some salts break down, releasing gases.

1. Identification of cations

• Warm the test tube for about a minute and observe the colour of the residue as it warms and cools. Observation of changes gives suggestions about the presence of cations, which can not be taken as conclusive proof.

• Estimation from the colour of salt in cold and on warming

• Blue to White Cu2

• Green to dirty white or yellow Fe2

• White to yellow Zn2

• Pink to blue Co2

 

    2. Identification of anions

• Radicals are first linked on the basis of primary tests.

• The dry heat test is one of the first primary tests performed that can give some important information about the acid radical presence.

• Other primary tests are grounded on the fact that CO32-, S2-, NO2-and SO32- react with dilute H2SO4 to give CO2, H2S, NO2 and SO2 gases.

• These, upon identification, indicate the nature of the ions present in the salt.

• Cl-, Br-, I-, NO3-and C2O42-and CH3COO- react with the concentrate. H2SO4 but not diluted, to produce H2SO4 characteristic gases.

• SO42-and PO43- react neither with diluted H2SO4 nor with concentrated. H2SO4

• . Thus, these are linked by individual tests.