Question

When potassium cyanide (KCN) reacts with acids, a deadly poisonous gas, hydrogen cyanide(HCN), is given off: KCN9aq) +HCL(aq) ---> HCN(g) + KCL(aq) If a sample of 0.310g of KCN is treated with an excess of HCL, calculate the amount of HCN formed in grams. ________?

Answer 1

Given reaction: KCN(aq) +HCL(aq) ---> HCN(g) + KCL(aq)

From the reaction, 1 mole of KCN reacts with one mole of HCl and produces one mole of HCN gas.
Given, the mass of KCN = 0.310 g and HCl is in excess. Therefore, KCN is the limiting reagent.

no. moles of KCN = mass. of KCN/gram.mol.Wt
               = 0.31 g/ 65.12 g/mol
               = 0.00476 moles
              
No. moles of HCN = no. moles of KCN
               = 0.00476 moles
Mass of HCN = no. moles of HCN x gram.mol.wt. of HCN
           = 0.00476 moles x 27 g/mol
           = 0.129 g
Therefore, the mass of HCN produced = 0.129 g