Question #177503

30cm^{3} of hydrogen was collected over water at 27°c and 750mmhg, if the vapor pressure of the water at the temperature of the experiment was 100mmhg. Calculate the volume of the gas of 760mmhg and 27°c

330cm

Expert's answer

**Q177503**

30cm^{3} of hydrogen was collected over water at 27°c and 750mm Hg. If the vapor pressure of the water at the temperature of the experiment was 100mm Hg. Calculate the volume of the gas of 760mmhg and 27°c.

**Solution : **

We have to find the volume of the dry hydrogen gas ( without any water ) at 760 mm Hg and 27^{ o}C.

Let us first find the partial pressure of hydrogen gas at 27^{ o}C.

Total pressure = Partial pressure of hydrogen gas + vapor pressure of water vapor.

"750\\space mm\\space Hg = Partial\\space pressure\\space of\\space hydrogen\\space gas + 100\\space mm\\space Hg"

"Partial\\space pressure\\space of\\space hydrogen\\space gas = 750\\space mm\\space Hg - 100\\space mm\\space Hg"

"Partial\\space pressure\\space of\\space hydrogen\\space gas = 650\\space mm\\space Hg"

**Hence the partial pressure of hydrogen gas in the collected moist hydrogen gas will be 650 mm Hg. **

**Step 2 : **

**We have to find out the volume occupied by pure hydrogen gas at 760 mm Hg and 27**^{0}**C. **

The temperature is the same. Only the pressure is changed.

The pressure of hydrogen gas, P_{1} = 650 mm Hg,

the initial volume of hydrogen gas, V_{1} = 30 cm^{3}.

New pressure of hydrogen gas, P_{2} = 760 mm Hg.

new volume of hydrogen gas, V_{2} =?

We can use Boyle's law, P1 V1 = P2 V2, and find the new volume occupied by hydrogen gas.

divide both the side by 760 mm Hg, we have

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