Question

Aluminum reacts with excess hydrochloric acid to form aqueous aluminum chloride and 111.1 ml of hydrogen gas over water at 26°C and 0.82 atm. (Vapor pressure of water at 26ºC = 25.2 mmHg.) How many grams of aluminum reacted?

Answer 1

Al reacts with water to form AlCl3 and H2 gas

2 Al(s) + 6 HCl(aq) ----------> 2 AlCl3(aq) + 3 H2(g)

2 moles of Al produces 3 moles of H2 gas

Given that, Vol. of H2 = 111.1 mL - 0.111L, Temp. = 26+273 = 299 K, Pressure = (0.82 atm - 0.033 atm) = 0.787 atm

Ideal gas equation is given by, PV=nRT

n = PV/RT = 0.787*0.111/0.0821*299 = 0.0035 moles

No. of moles of H2 gas produced = 0.0035 moles

Since, 2 moles Al = 3 moles H2

then x ? = 0.0035 moles

x = 2*0.0035/3 = 0.0023 moles of Al

Amount of Al = moles * molar mass = 0.0023*27 = 0.063 gms