A red solid is insoluble in water. However, it becomes soluble if some KI is added to water. Heating the red solid in a test tube results in liberation of some violet coloured fumes and droplets of a metal appear on the cooler parts of the test tube. The red solid isa)(NH4)2Cr2O7b)HgI2c)HgOd)Pb3O4Correct answer is option 'B'. Can you explain this answer?

Question

Answer

HgI2 is red and insoluble and also when heated iodine vapours which are violet in colour are liberated

Answer

Answer

The red solid is HgI2 (Mercury(II) iodide).

Insolubility in water:

HgI2 is a red solid that is insoluble in water. This means that when it is added to water, it does not dissolve and remains as a solid.

Effect of adding KI:

When some KI (potassium iodide) is added to water, it forms a solution. This solution can dissolve the red solid HgI2. The reaction can be represented as follows:
HgI2 (s) + 2KI (aq) → HgI4^2- (aq) + 2K+ (aq)

The addition of KI allows the red solid to become soluble in water by forming a complex ion, HgI4^2-. This complex ion is soluble in water.

Heating the red solid:

When the red solid HgI2 is heated in a test tube, it undergoes a decomposition reaction. The heat causes HgI2 to decompose into mercury(I) iodide (HgI) and iodine gas (I2). The reaction can be represented as follows:
2HgI2 (s) → 2HgI (s) + I2 (g)

The violet colored fumes observed during heating are due to the sublimation of iodine gas. The droplets of metal that appear on the cooler parts of the test tube are mercury(I) (Hg) formed as a result of the decomposition of HgI2.

Identification of the red solid:

Based on the observations, the red solid is HgI2 (Mercury(II) iodide). It is insoluble in water but becomes soluble when KI is added. Heating the red solid results in the liberation of violet colored fumes (iodine gas) and the formation of droplets of mercury(I) on the cooler parts of the test tube.

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