When `2.96 g of ` mercuric chloride is vaporised in a 1-litre bulb at 680 K, the pressure is 458 mm. What is the molecular weight and molecular formula of mercuric chloride vapour ? (Hg = 200.6)

Explanation

Let M be the moleclar weight of mercuric chloride.
No. of moles of the mercuric chloride vepour `= (2.96)/(M).`
Again from the gas equation `pV = nRT,`
no. of moles `= n = (pV)/( RT) = (((458)/(760))xx 1)/(0.0821 xx 680)`
where `p = (458)/(760) atm, V =1 ` litre, R = 0.0821` lit. `atm `K ^(-1) mol ^(-1) and T = 680 K.`
Hence, `(2.96)/(M) = ((458)/(760)xx 1)/(0.0821 xx 680)`
` M = 274.`
Since `Hg Cl _(2)` has a molecular weight of `(200.6 + 2 xx 35.5) = 271.6` which is nearly equal to the calculated value of `274,Hg Cl _2)` is he molecular formula for mercuric chloride.