Question

1. A 34.32 mL sample of O2 gas was collected over water at 24 oC from the decomposition of hydrogen peroxide. The barometric pressure in the room that day was 746.32 torr.

A. Calculate the pressure of O2 gas in the system.

B. Calculate the moles of gas collected.

C. Calculate the moles of H2O2 initially present in the sample.

Answer 1

a)

Pgas = PTotal - Pvapor

Pvapor = 22.4 torr

Ptotal = 746.32 torr

Pgas = 746.32 -22.4

Pgas = 723.92 torr

b)

moles of gas collected

Apply Ideal Gas Law,

PV = nRT

where

P = absolute pressure

V = total volume of gas

n = moles of gas

T = absolute Temperature

R = ideal gas constant

P V= nRT

n = PV/(RT)

n = (723.92 )(34.32*10^-3)/(62.4*(24+273))

n = 0.0013405 mol of gas

c)

ratio :

H2O2 --> H2O + 1/2O2

mol of O2 = 0.0013405

then, mol of H2O2 = 2*mol of O" = 2*0.0013405 = 0.002681 mol of H2O2