Question

# (a) The diagram given below is to prepare iron (III) chloride in the laboratory: Figure (i) What is substance B? (ii) What is the purpose of B? (iii) Why is iron (III) chloride to be stored in a closed container? (iv) Write the equation for the reaction between iron and chloride. (b) Write the equation(s) for the reaction(s) to prepare lead sulphate from lead carbonate.

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Solution

## (i) Substance B is anhydrous (fused) calcium chloride (${\mathrm{CaCl}}_{2}$). (ii) Anhydrous calcium chloride absorbs the moisture present in the apparatus. This helps in keeping the anhydrous ferric chloride dry as it is a highly deliquescent salt. (iii) Iron (III) chloride should be stored in a closed container because of its deliquescent nature. In the presence of moisture, iron (III) chloride absorbs water, gets dissolved in it and forms a saturated solution. (iv) When dried chlorine gas is passed over heated iron, it forms anhydrous iron (III) chloride. $2\mathrm{Fe}+3{\mathrm{Cl}}_{2}\to 2{\mathrm{FeCl}}_{3}\phantom{\rule{0ex}{0ex}}\mathrm{Anhydrous}\phantom{\rule{0ex}{0ex}}\mathrm{iron}\left(\mathrm{III}\right)\mathrm{chloride}\phantom{\rule{0ex}{0ex}}$ (b) The preparation of lead sulphate from lead carbonate involves the following steps: Step I: Insoluble lead carbonate first reacts with dilute nitric acid to form soluble lead nitrate. ${\mathrm{PbCO}}_{3}+\mathrm{dil}.2{\mathrm{HNO}}_{3}\stackrel{}{\to }\mathrm{Pb}\left({\mathrm{NO}}_{3}{\right)}_{2}+{\mathrm{H}}_{2}\mathrm{O}+{\mathrm{CO}}_{2}\phantom{\rule{0ex}{0ex}}\mathrm{Lead}\mathrm{carbonate}\mathrm{Nitric}\mathrm{acid}\mathrm{Lead}\mathrm{nitrate}\left(\mathrm{Soluble}\right)$ ​ Step II: Dilute sulphuric acid is then added to lead nitrate to form lead sulphate and nitric acid. $\mathrm{Pb}\left({\mathrm{NO}}_{3}{\right)}_{2}+\mathrm{dil}.{\mathrm{H}}_{2}{\mathrm{SO}}_{4}\stackrel{}{\to }{\mathrm{PbSO}}_{4}+2{\mathrm{HNO}}_{3}\phantom{\rule{0ex}{0ex}}\mathrm{Lead}\mathrm{nitrate}\mathrm{Sulphuric}\mathrm{acid}\mathrm{Lead}\mathrm{sulphate}\mathrm{Nitric}\mathrm{acid}$

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