Question

Sal R is black in colour. On reacting with conc. HCl, it liberates a pungent greenish yellow gas which turns moist starch iodide paper blue black.

Answer 1

It is Manganese Dioxide (MnO2)

Explanation:

• As we know that the gas emitted is pungent and greenish in color, this shows the gas is chlorine gas
• The chlorine gas also turns moist starch iodide paper blue
• Also when this salt has reacted with the concentrated HCl acid, the salt is also black
• This shows it is Manganese Dioxide (MnO2)
• Reaction 1         MnO₂ + 2 HCl → MnCl₂ + Cl₂(g)↑ +H₂O
• Reaction 2        2KI(aq) + Cl₂(g) → KCl(aq) + I₂(s) Black solid