Question

A 0.120 gram sample of Zn reacts with an excess of hydrochloric acid and produces 46.5 mL of H2 gas which is collected over water at a barometric pressure of 748 mm Hg and at 23 °C. The vapor pressure of water at 23 °C is 21 mm Hg. What is the molar mass of Zn?

Answer 1

The question is based on the concept of analytrial Chemistry Volume of the collected = 46.5 m2 = 46.5x103 L o the collected over water Pressure observed = pressure of H₂ Pressure of water 748 mmily = Pressuretty + 21 mmHg Pre = (746-21) monty Pr₂ = 727 mmHg : 760 mm Hg = 1 atm i 727 mm Hg = Latm x 727 mmiling I 760 mmila PH2 = 0.9566 atm T= 23C = 23+273 = 296k Calculating number of moles of H₂ PV=nRT na bu RT

n= 0.9566 4 4 6,5x103 atm 4 0.0821 x 296K Catonmotky (n= 1.83 x103 moles of H₂ The reaction taking place is; Zn +2HQ ZnCl2 + H₂ It is clear from equation that Imol of Hy are produced from Imol 1., 1.83x103 mol ". 1183 xlo3 moles of Zn mass of 2n takenz o. 120g Moles= mass molar mass molar mass = mass moles = 0.120g 1.83x103 mol molarmass= 65.57 g/mol This molar mass of Zn was found to be 65.57 glonol.