Question

State your observations when following salts are heated strongly in dry state. Write chemical equations in support of your answer.

Iodine crystals $\left({\mathrm{I}}_2\right)$

Answer 1

Dry heat test: A sample of the substance is taken in a test -tube and heated first gently, then strongly in a flame and observations are recorded. It is a method of qualitative analysis.

• Qualitative analysis: The analysis which aims at detecting the presence of any substance in a given sample.

Observations:

On heating steel grey Iodine crystals$\left({\mathrm{I}}_2\right)$, the following observations are recorded:

• Iodine crystals show sublimation and violet-coloured Iodine vapours are seen.
• These vapours condense and again turn into shining grey crystals when cooled.

Sublimation: The process of direct conversion of solid into gaseous form without turning into a liquid state.

• There is no change in the composition of the substance during sublimation.
• Example: Iodine $\left({\mathrm{I}}_2\right)$

Chemical equation:

Iodine shows the process of sublimation on heating as shown below:

$\underset{(\mathrm{Iodine}\mathrm{crystals})}{{\mathrm{I}}_2\left(\mathrm{s}\right)}\underset{\mathrm{Cooling}}{\overset{\mathrm{Heating}}{\rightleftharpoons }}\underset{(\mathrm{Iodine}\mathrm{vapours})}{{\mathrm{I}}_2\left(\mathrm{g}\right)}$

• Iodine crystals are dark purple to steel grey (almost black) in colour
• Iodine vapours are deep purple coloured.