Question

1.1 A sample of gas weighing 0.028 6 g occupies a volume of 50 cm at 76 cmHg and
25 °C. What is the molar mass of the gas?
(Ans. 141.33 g mol-')
1.2 What is the density of helium at 500 °C and 100 mmHg pressure?
10-2
-3​

Answer 1

Explanation:We can find the molar mass MM of this gas using the equationMM=dRTP whered is the density of the gas, in g/L R is the universal gas constant, equal to 0.082057L∙atmmol∙K T is the absolute temperature of the gas, in K P is the pressure of the gas, in atm We need to convert some units to get where we need to be. Let's do the density first.1 L is equal to 1 dm3 , which is equal to 103 cm3 , so the density is(0.0286lg50cm3)(103cm31dm3)(1dm31lL)=0.572 g/L Degrees centigrade is the same as degrees Celsius, so let's convert this to K by adding 273: T = 25*C + 273=298 KLastly, let's convert our pressure, which is in centimeters of mercury:76cm Hg(10mm Hg1cm Hg)(1latm760mm Hg)=1 atm Now that we have all our values, let's plug them into the equation:MM=(0.572gL)(0.082057L∙atmmol∙K)(298K)1atm =14.0 g/mol

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