The reaction of magnesium with hydrochloric acid at 30 °C and 817.36 mmHg produced 4.03 L of hydrogen that was collected over water. The vapour pressure of water at 30 °C is 33.4 mmHg. How many moles of hydrogen were formed?

1 Answer
Nov 12, 2016

Answer:

#1.67\times10^-1color(white)(l)"mol"#

Explanation:

The Reaction:

#Mg(s)+2HCl(aq)\rightarrowMgCl_2(aq)+H_2(g)#

Data given:

Pressure #P="817.36 mmHg"#
Volume #V="4.03 L"#
Temperature #T="303 K"#

Work :

#P_"total" = P_"H₂" + P_"H₂O"#

At 303 K, #P_"H₂O" = "33.4 mmHg"#

#P_"H₂" = P_"total" - P_"H₂O" = "817.36 mmHg" - "33.4 mmHg" = "783.96 mmHg" = "1.0315 atm"#

Apply the Ideal Gas Law #PV=nRT# to get #n = \frac(PV)(RT)#

The constant #R = "0.0821 L·atm·K"^"-1""mol"^"-1"#

#\frac("1.0315 atm"\times"4.03 L")("0.0821 L·atm·K"^"-1""mol"^"-1"\times"303 K") = 1.67\times10^-1color(white)(l)"mol"#