5. Redox and stoichiometry Cl2(g) can be prepared from a mixture of potassium di

Question

5. Redox and stoichiometry Cl2(g) can be prepared from a mixture of potassium dichromate, K2Cr2O7 and hydrochloric acid, HCl. If 62.6 g of 98.5 % K2Cr2O7 solid reacts with 325 ml of HCl (density 1.15 g/ml, 30.1 % HCl by mass), what volume of Cl2 (g) is collected over water at 25 oC and 1 atm. The vapour pressure of water at 25 oC is 23.76 torr. Cl^-(aq) + Cr2O7^2- (aq)>>>Cl2(g) + Cr^+3 (aq).

Explanation / Answer

no. of moles of K2Cr2O7 taken = 62.6*0.985/294 = 0.209 moles no. of moles of HCl taken = 1.15*325*0.301/36.5 = 3.08 moles balance chemical equation ==> K2Cr2O7 + 14(HCl) ===> 2(KCl) + 3(Cl2) +2(CrCl3) + 7(H2O) 1 mole k2cr2o7 requires 14 mole hcl => 0.209 moles of k2cr2o7 would require 14*0.209 moles = 2.96 moles of HCl hence k2cr2o7 is the limiting reagent.. => no. of mole of Cl2 formed when 0.209 moles of K2cr2o7 is consumed = 0.209*3 = 0.627 moles at 25 deg C and 1 atm 1 mole of gas occupies a volume of 22.4 L => 0.627 moles of cl2 will have volume = 22.4*0.627 = 14.04 L = answer vapor pressure of water is just an additional information provided.

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