Problem 4

A mixture contains two organic compounds, A and B, both containing oxygen and miscible in all proportions. Controlled oxidation of this mixture yields a single compound C, which forms an addition compound with

\ce{NaHSO3}

. The molar mass ratio of this bisulfite adduct to compound C is 2.7931. Burning the mixture of A and B with a stoichiometric amount of air (20 %

\ce{O2}

, 80 %

\ce{N2}

by volume) yields a gas mixture of total volume 5.432 dm

^3

at STP. When bubbled through

\ce{Ba(OH)2}

solution, the volume decreases by 15.46 %. (a) Identify compounds A, B and C. (b) Calculate the molar ratio of A and B in the initial mixture. (

A_r(\text{C}) = 12

A_r(\text{O}) = 16

A_r(\text{S}) = 32

A_r(\text{Na}) = 23

)

Step 1 of 4: Identify compound C

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\dfrac{M(\ce{C}) + 104}{M(\ce{C})} = 2.7931 \Rightarrow M(\ce{C}) = \dfrac{104}{1.7931} = 58\ \text{g mol}^{-1}

Analysis

Addition of $\ce{NaHSO3}$ ( $M = 104$ ) to a carbonyl gives $\ce{R2C(OH)SO3Na}$ of mass $M(\ce{C}) + 104$ . The ratio $2.7931$ yields $M(\ce{C}) = 58$ g mol $^{-1}$ , which is propanone (acetone, $\ce{CH3COCH3}$ ). Hence B is acetone and A is propan-2-ol (isopropanol, $\ce{CH3CH(OH)CH3}$ , $M=60$ ), which oxidises to acetone.