what effect would each of the following have on the calculated molar mass of an
ID: 895565 • Letter: W
Question
what effect would each of the following have on the calculated molar mass of an unknown?
a) The balance was not zeroed before the three weighings of the test tube, sample, water were made. This caused each mass measurement to be 0.102 g greater than it should have been.
b) The thermometer consistently read 0.06 C lower than it should have, over the entire experimental range
c) The masses of the unknown and the solvent (water) were determinded, and the unknown completely dissolved in the water. Just before the jacketed test tube containing the unknown solution was placed in the ice-salt water bath, a small amount of the solution was spilled out of the tube.
d) The unknown contained a smal amount of an insoluble impurity
e) The unknown contained a small amount of a soluble impurity, which had a molar mass lower than that of the pure unknown.
f) A portion of the unknown did not dissolve.
Explanation / Answer
The effect on the calculated molar mass of an unknown would be,
a) The balance was not zeroed before the three weighings of the test tube, sample, water were made. This caused each mass measurement to be 0.102 g greater than it should have been.
molar mass would be higher then actual value.
b) The thermometer consistently read 0.06 C lower than it should have, over the entire experimental range
If the thermometer read lower temperature then actual value, the difference between the temperature deltaT would be higher and so the molar mass will also be higher.
c) The masses of the unknown and the solvent (water) were determinded, and the unknown completely dissolved in the water. Just before the jacketed test tube containing the unknown solution was placed in the ice-salt water bath, a small amount of the solution was spilled out of the tube.
If liquid containing the unknown is spilled, the molar mass would be lower.
d) The unknown contained a smal amount of an insoluble impurity
If the unknown contained an insoluble impurity, the actual mass will be different than measured, so molar mass will be lower
e) The unknown contained a small amount of a soluble impurity, which had a molar mass lower than that of the pure unknown.
Overall this would reduce the molar mass of the unknown.
f) A portion of the unknown did not dissolve.
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