Question

An ore on treatment with dilute hydrochloric acid produces brisk effervescence to produce a colourless and odourless gas. What type of ore is this? What operation will be required to obtain metal from it?

Answer 1

(a) Brisk effervescence with an acid is produced due to the evolution of Carbon dioxide $\left({\mathrm{CO}}_2\right)$ gas which is colourless and odourless gas on reaction of an acid with carbonate ore. Example:

• $\underset{(\mathrm{Zinc}\mathrm{carbonate})}{{\mathrm{ZnCO}}_3\left(\mathrm{s}\right)}+\underset{(\mathrm{Dil}.\mathrm{Hydrochloric}\mathrm{acid})}{\mathrm{HCl}\left(\mathrm{aq}\right)}\to \underset{(\mathrm{Zinc}\mathrm{chloride})}{{\mathrm{ZnCl}}_2\left(\mathrm{s}\right)}+\underset{(\mathrm{Carbon}\mathrm{dioxide})}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$
• So the ore is a carbonate ore.

(b) The process of calcination followed by reduction is required to obtain a metal from its carbonate ore.

Step-1: Calcination

When a carbonate ore is heated in the limited supply or absence of air, the carbonate ore gets converted into its oxide ore after releasing carbon dioxide.

• Hence, by the calcination process the metal carbonate ore are converted to their metal oxides a shown below.
• $\underset{(\mathrm{Zinc}\mathrm{carbonate})}{{\mathrm{ZnCO}}_3}\underset{(\mathrm{Zinc}\mathrm{oxide})}{\stackrel{∆}{\to }\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{(\mathrm{Carbon}\mathrm{dioxide})}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

Step-2: Reduction with carbon

Oxide ore is heated with carbon which acts as a reducing agent and helps to extract the metal i.e.; Zinc.

• $\underset{\left(\mathrm{Zinc}\right)}{\mathrm{ZnO}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Carbon}\right)}{\mathrm{C}\left(\mathrm{s}\right)}\to \underset{\left(\mathrm{Zinc}\right)}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{(\mathrm{Carbon}\mathrm{moonoxide})}{\mathrm{CO}\left(\mathrm{g}\right)}$