A laboratory piston–cylinder apparatus keeps a gas sample at a constant pressure of…

CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance

Problem

A laboratory piston–cylinder apparatus keeps a gas sample at a constant pressure of 100 kPa100\,\text{kPa} while its temperature is varied. The measured volumes at several temperatures are listed below. Temperature TT (K): 290 310 330 350 370 Volume VV (m3^{3}): 2.40×10−32.40\times10^{-3} 2.56×10−32.56\times10^{-3} 2.72×10−32.72\times10^{-3} 2.88×10−32.88\times10^{-3} 3.04×10−33.04\times10^{-3} The gas sample has a measured mass of 1.20 g1.20\,\text{g}. (a) Plot volume VV (vertical axis) versus temperature TT (horizontal axis) and draw a best-fit straight line through the data. (b) Using two clearly indicated points on your best-fit line, calculate its slope and state the units of that slope. (c) From the numerical value of the slope, determine the number of moles of gas present in the cylinder. (d) Using your result from part (c), compute the molar mass of the gas. Hence identify whether the sample is more likely to be helium (4.00 g mol−14.00\,\text{g mol}^{-1}) or neon (20.2 g mol−120.2\,\text{g mol}^{-1}), clearly justifying your choice.

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