Chemistry Labs

Problem 1

An amount of 23 g of a gas (density ρ=2.05\rho = 2.05 g dm−3^{-3} at STP) when burned gives 44 g of carbon dioxide and 27 g of water. What is the structural formula of the gas (compound)?
Step 1 of 3: Molar mass from density
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M=ρRTp=2.05×22.4=46 g mol−1;n(X)=2346=0.5 molM = \dfrac{\rho R T}{p} = 2.05 \times 22.4 = 46\ \text{g mol}^{-1}; \quad n(X) = \dfrac{23}{46} = 0.5\ \text{mol}
Analysis

One mole of an ideal gas at STP occupies 22.4 dm3, so M=ρ×22.4=46M = \rho \times 22.4 = 46 g mol−1^{-1}; the 23 g sample is 0.5 mol.