A sample of helium is collected by displacing 145 mL of wate

A sample of helium is collected by displacing 145 mL of water. The pressures of the gas and the atmosphere are equalized using the method described in this experiment. The atmospheric pressure is 745 The temperature of the water and that of the gas are identical at 26°C. How many moles of helium have been evolved? 2. mmHg.

Solution

Using Ideal Gas Law:

PV= nRT

P is pressure in atm

Vis volume in litre

R is gas constant

T is temperature in Kelvin

P = 745mmHg

1atm = 760mmHg

P in atm = 745/760 atm

Volume = 145 /1000 L

R is 0.0821 LatmK^-1mol^-1

T in K = 26+273K

745/760*145/1000 = n *0.0821*299

n= 5.79 millimoles