Question

in this lab, you will start off by calculating the number of moles of air molecules inside a flask containing 20 ml of water by cooling the flask down to near 0°c and assuming the vapour pressure of water is negligible at that temperature. if the volume of the air inside the flask is 147 ml, the gas pressure sensors reads 101.6 kpa and the temperature sensor reads 0.3 °c, how many moles of air are present in the flask? express your answer in mol. assume r = 8.314 j mol⁻¹ k⁻¹.

Explanation:

Step1: Convert units

• Convert volume \(V = 147\space mL=147\times10^{- 3}\space L = 147\times10^{-6}\space m^{3}\)
• Convert pressure \(P = 101.6\space kPa = 101600\space Pa\)
• Convert temperature \(T=(0.3 + 273.15)\space K=273.45\space K\)

Step2: Use ideal gas law \(PV = nRT\)

Solve for \(n\), \(n=\frac{PV}{RT}\)
Substitute \(P = 101600\space Pa\), \(V = 147\times10^{-6}\space m^{3}\), \(R = 8.314\space J\space mol^{-1}\space K^{-1}\), \(T = 273.45\space K\)
\(n=\frac{101600\times147\times10^{-6}}{8.314\times273.45}\)

Step3: Calculate the value of \(n\)

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Answer:

\(6.57\times 10^{-3}\space mol\)