Posted by chuchuchulu on Wednesday, February 24, 2010 at 12:01am.
We don't know which experiment you did nor how it was done unless you tell us. My crystal ball is hazy tonight.
its Molecular mass by freezing point depression. and its a pre-lab
You must read the thermometer twice, once to determine the normal freezing point and again to determine the depressed freezing point. So if the thermometer reads too high, then it read too high each time by 1.4 degrees; therefore, the difference in delta T (delta T = Kf*m) does not change. Thus the experimental change in molality (and on into molecular mass) is not changed. That's one reason, in analytical chemistry, why we weigh by difference. Instead of weighing a sample by placing it on the pan of the balance, we measure the bottle containing the sample, remove some sample and weigh the bottle and sample again. The difference tells us how much was removed and that amount is placed in a separate container to do the experiment. Thus, if a weight is slightly off, it tends to correct itself.
thank you so very much.do you know the answers to these:
(b) Some of the solvent was spilled before the solute was added.
(c) Some of the solute was spilled after it weighed and before it was added to the solvent.
(d) Some of the solutions was spilled after the solute and solvent were mixed but before the freezing point was determined.
I did b in detail above. Use the same kind of reasoning on c and d. Use the same three equations I used above in answering b. d won't change the result. It just means you have less sample to determine delta T on but the molality doesn't change by spilling a drop or more after everything is mixed.
Does this affect the Calculated molar Mass?
only on Tuesdays
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