sole wilthe reported molar mass ofthe soute betoo hgh b) loaOw. crepo sane al a

Question

sole wilthe reported molar mass ofthe soute betoo hgh b) loaOw. crepo sane al a thermometer is mscaitra ed to reed 1°C higher than the actual temperaure ove s eme Hint. Follow a complete se1-up for the calculation to see the eflect of the error Explain b) If te cyclchexane is initaly contamnated wth a soluble nen-reactive, nonvolatile sutrit ance, w -change inteezing portal be a) higher b) lower, or the line a·the urortarinated cydohecane? 5) Explain why the treeang pont of a pure sovent is constamt whereas the teezing pom of solution decreases with steady cocing -1t-

Explanation / Answer

c) The same is correct option

If thermometer is miscalibrated to read 1.0 oC higher than the actual temperature over its entire scale, the reading of the normal freezing point is 1 degree too high and the reading for the freezing point of the solution containing the solute is also 1 degree too high, so there will be no effect on the reported molar mass of the solute.

For example:

If normal freezing point = 4.5oC, freezing point of solution = 4.0oC

Difference = 5.0 oC - 4.5 oC = 0.5 oC

Now suppose the thermometer reads 1 degree higher

Normal freezing point =   4.5oC + 1 oC = 5.5 oC

Freezing point of solution = 4.0 oC + 1 oC = 5 oC

Difference = 5.5 oC – 5.0 oC = 0.5 oC

When solute is added to solvent, there will be decrease the freezing point of the solvent.

The decrease in freezing point, Tf of solvent is proportional to the molal concentration, m, of the solute.

Tf = Kf m

Kf is molal freezing point depression constant

m = Tf / Kf

When,

Molal concentration of solute is calculated, we can calculate molar mass.

b)

c. The same as the uncontaminated cyclohexane is correct option.

Cyclohexane is contaminated with a soluble non-reactive, non-volatile substance, so there will be no change in freezing point, Tf.

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