Question

1. Aluminum reacts with excess hydrochloric acid to form aqueous aluminum chloride and 156 ml of hydrogen gas over water at 26°C and 0.956 atm. (Vapor pressure of water at 26ºC = 25.2 mmHg.)     How many grams of aluminum reacted? Enter to 3 decimal places.

Answer 1

Solution-  From the ideal gas equation

PV = nRT
n = PV/RT = moles H2

P = 726.55 mmHg x (1 atm / 760 mmHg) = 0.955 atm
V = 0.156 L
R = 0.0821 Latm/moleK
T = 27C = 26+273 = 299 K

n = (0.955 atm)x(0.156 L) / [ (0.0821 Latm/moleK) x (299 K) ]
n = 0.00606 moles H2

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

from balanced equation, 2 moles Al ---> 3 moles H2

0.00606 moles H2 x (2 moles Al / 3 moles H2) = 0.00404 moles Al

Now

0.00404 moles Al x (27.0 g/mole) = 0.10908 g Al