Question

A piece of sodium metal reacts completely with water
according to the reaction:
2Na(s) + 2H2O(l) 2NaOH(aq) + H2(9)
The hydrogen gas is collected over water at 25°C. The volume
of the gas generated is 246 mL at 760.0 mmHg.
Calculate the volume of dry hydrogen gas that would be
collected at STP.
_mL H2

Answer 1

Answer: 225 ml

Explanation:

246 ml of hydrogen gas is collected at standard pressure (760.00 mmHg) but at 25°C, instead of the standard temperature of 0°C.  We can use the combined gas law to calculate a revised volume based on the standard temperature:

P1V1/T1 = P2V2/T2  where P,V, and T are the Pressure, Volume and Temperature at initial (1) and final (2) conditions.

Pressure remains the same, so it cancels:

V1/T1 = V2/T2

We want V2, so rearrange:  V2=V1(T1/T2)

Temperatures must be in Kelvins:

V2 = (246ml)*(296.25K/273.15K)

V2 = 225 ml to 3 sig figs