I. Melting point I A. What effect would rapid heating of a sample have on the ob

Question

I. Melting point I A. What effect would rapid heating of a sample have on the observed melting point. Briefly explain. 3pts (mp dun'-te Ybe, napr..ige et nex cuotai'): nan B. Molecular weights can be measured by the freezing point depression measurements. A 6.0g sample of a compound whose empirical formula is (CH2) is dissolved in 200g of benzene. The freezing point of the solution is 1.83 below that of pure benzene. The molal freezing point depression constant for benzene is 5.12 /m. Determine the molecular weight and correct molecular formula of the compound. Note: AT-iKr.m 8pts II. Boiling point ? A. What will be the effect on the normal boiling point of a pure liquid if a non-volatile 3pts impurity is added? Briefly explain a puse hqciol usll increase it a ng When determining the boiling point of a liquid, why should the water or oil bath be heated slowly? B. to male ust 0% ed aer oest slate

Explanation / Answer

1. freezing point depression

A. is correct, rapid heating will give more heat which leads to overheating and temperature shoot up. Higher temperature reading will be read than the actual value.

B. given dTf = 1.83

mass of benzene = 200 g = 0.2 kg

molality of solute = 6 g/molar mass x 0.2 kg

Kf = 5.12 oC/m

i = 1

using,

dTf = i.Kf.m

molar mass of solute = 1 x 5.12 x 6/0.2 x 1.83 = 84 g/mol

So, molar mass/empirical formula mass = 84/14 = 6

molecular formula = C6H12

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II. boiling points

both A. and B. are answered correctly above.

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