Question

In the course of research, a chemist isolates a new compound with an empirical formula C3H3O2. 4.97 g of the compound when dissolved in 100. g of water produces a solution with a freezing point of −0.325°C. What is the molecular formula of the compound? (For water, Kf = 1.86°C/m.) (For your answer, enter the integer that tells the number of multiples of the empirical formula present in the molecular formula.)

Answers

You can find the molal concentration (m) from 0.325degC/(1.86degC/m)

m=(number of moles)/0.1 kg

hence find number of moles.

molecular mass = (mass used)/(number of moles)= 4.97g/(number of moles).

RMM of C3H3O2 = 71

multiple = molecular mass/71

As a point of interest a compound that only contains C, H and O must have an even numebr of hydrogen atoms. Hence the multiple must be an even number.

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