Question

1a) Ten drops of 1.0M Na₂CO₃ are placed into each of two small test tubes. To the first test tube, 2 drops of 0.1 M Ca(NO₃)₂ is added, and to the second test tube, 2 drops of 0.1M Mg(NO₃)₂ is added. Describe the likely observations for each test tube and state how these results could or could not be used to distinguish between the cations.

b) Six drops of 0.5M bromine in organic solvent is placed in each of two small test tubes. To the first test tube, 15 drops of 0.1NaBr is added, and to the second test tube, 15 drops of 0.1M NaI is added. Describe the likely observations for each test tube and state how these results could be used to distinguish between the anions.

Answer 1

a) Reaction that takes place in test tube1.

Na₂CO_{3 +}Ca(NO₃)₂ CaCO_3(s) +2NaNO₃

Reaction that takes place in test tube2.

Na₂CO_{3 +}Mg(NO₃)₂ MgCO_3(s) +2NaNO₃

In both cases white precipitates are obtained ,so it is not possible to distinguish between the cations as either Mg2+ or Ca2+ ,both gives white colored carbonates.

b)Br2 in organic solvent acts as an Oxidising agent .The oxidizing capability is in the order Cl2>Br2>I2 for halogens.

So Br2 oxidizes I- to I2

Br2+2NaI--->I2+2NaBr ,I2 gives purple color in organic layer thus identified

Hence,Br- or I- anion can be distiguished by performing this test

Br2+NaBr--->No reaction (light colored solution)