Chemistry Practice Problems Collecting Gas Over Water Practice Problems Solution: Small quantities of hydrogen can be prepared by th...

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Solution: Small quantities of hydrogen can be prepared by the addition of hydrochloric acid to zinc. A sample of 195 mL of hydrogen was collected over water at 25 °C and 753 torr. What mass of hydrogen was collected? (Pwater = 24 torr at 25 °C)A. 0.00765 g B. 0.0159 g C. 0.0154 g D. 0.0164 g E. 0.159 g

Problem

Small quantities of hydrogen can be prepared by the addition of hydrochloric acid to zinc. A sample of 195 mL of hydrogen was collected over water at 25 °C and 753 torr. What mass of hydrogen was collected? (Pwater = 24 torr at 25 °C)

A. 0.00765 g 

B. 0.0159 g 

C. 0.0154 g 

D. 0.0164 g 

E. 0.159 g

Solution

We’re being asked to determine the mass of the 195 mL hydrogen sample collected over water at 25 °C and 753 torr.

At STP:         T = 0°C

                      P = 1 atm


We’re going to calculate the volume of the gas using the ideal gas equation.

PV=nRT

P = pressure, atm
V = volume, L
n = moles, mol
R = gas constant = 0.08206 (L·atm)/(mol·K)
T = temperature, K


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