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 3 of 4: Combustion balance for air

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\begin{cases} 3x + 3y = \dfrac{0.840}{22.4} = 0.0375\ \text{mol} \\ 18x + 16y = \dfrac{4.592}{22.4} = 0.2050\ \text{mol} \end{cases} \Rightarrow x = 0.0025,\; y = 0.0100\ \text{mol}

Analysis

Isopropanol ( $x$ mol) needs 4.5 O2 + 18 N2 and makes 3 CO2; acetone ( $y$ mol) needs 4 O2 + 16 N2 and makes 3 CO2. Solving $x + y = 0.0125$ and $9x + 8y = 0.1025$ yields $x = 0.0025$ mol and $y = 0.0100$ mol.