Wednesday
April 1, 2015

Homework Help: Chemistry

Posted by Jason on Sunday, June 2, 2013 at 10:52pm.

I just wanted to see if my answers made sense.

1. What effect would each of the following have on your calculated value of Kf (too high, too low, or no
effect)? In each case explain your answer.
a) There was a small bubble in the thermometer, causing all the temperature readings to be erroneously
high.
The Kf would be too high. Because the bubble was giving off higher temperature.

b) A student used a new thermometer for Part II, but failed to notice that some of the naphthalene from Part I was sticking to the old thermometer.
There would be no effect. The thermometer was not directly in contact with the solution.


c) After melting the naphthalene, small pieces of rubber from the stopper are seen floating in the solution.
No effect. the rubber can simply be taken out.

2. A student decided to use the same weighing boat he used to measure the biphenyl in Part II for
measuring his unknown in Part III. However, he failed to notice that a small amount of biphenyl was still
in the boat, which was transferred to the test tube with his 1g of unknown. What effect would this have on
each of the following (too high, low, or no effect)? In each case, explain your answer.
a) The measured delta Tf
Both would react causing the freezing point to be higher than it would be in reality.

b) The calculated molality of the solution
molal would be higher because there would be a high number of Kg per solvent.

c) The calculated molar mass of the unknown

Molar mass would be unaffected. Although i am not sure why.

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