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March 26, 2017

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Molecular Mass by Freezing point Depression (Preliminary Lab)


The following errors occurred when the above experiment was carried out. How would each affect the calculated molecular mass of the solute (too high,too low, no effect)? Explain your answer.

(a) The thermometer uses actually read 1.4C too high.

(b) Some of the solvent was spilled before the solute was added.

  • chemistry - ,

    I gave you the answer for a from your first post.
    For #2.
    (1) delta T = Kf*m
    (2) molality = moles solute/kg
    (3) molar mass = grams solute/# moles.

    So if some of the solvent is spilled before the solute is added, that will mean the molality is too large (equation 2). So when we measure delta T (equation 1) we see delta T too large. Now we go backwards. Delta T too large, m is too large(eqn 1), calculated moles is too large (eqn 2), and (from equation 3), molar mass is too small (because the denominator is too large). Check my thinking.

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