A student performed the freezing point depression experiment according to directions but mistakenly recorded the mass of lauric acid as 8.300g instead of8.003g. The calculated molar mass of the unknown acid will be GREATER/LESS than true value b/c mass of lauric acid appears in the denominator of the unknown acid's molecular weight determination, therefore, if it was mistakenly recorded too high, it would INCREASE/DECREASE the calculated moles of solute.
i think it's less, decrease. am i correct in my thinking?
deltaTf= mass/molarmass * K then
molarmass=mass*k/deltaTf
I don't kinow what the experiment is, but I do know that mass is not in the denominator here. So the question does not read correctly. Here is mass is too high, the calculated molar mass will be too high.
Actually, you are correct in your thinking. Let me explain in more detail how the mistake in recording the mass of lauric acid affects the calculated molar mass of the unknown acid.
In the freezing point depression experiment, the formula used to calculate the molar mass of a solute is:
molarmass = mass * K / deltaTf
Here, "mass" refers to the mass of the solute, "K" is the cryoscopic constant for the solvent, and "deltaTf" is the measured freezing point depression.
Since the mass of lauric acid appears in the numerator of the formula, an increase in the mass value would indeed increase the calculated molar mass of the unknown acid. However, the mistake here is that the mass of lauric acid is recorded as 8.300g instead of the correct value of 8.003g. Therefore, the recorded mass is actually higher than the real value.
When a higher mass value is used in the calculation, it would result in a higher molar mass value because the numerator (mass) is larger. So, the calculated molar mass of the unknown acid will be greater than the true value.
Additionally, it's important to note that the denominator of the formula does not involve the mass of the solute. The denominator is the value of deltaTf (freezing point depression) which is a measure of the change in freezing point caused by the presence of the solute.
To summarize, due to the higher recorded mass of lauric acid, the calculated molar mass of the unknown acid will indeed be greater than the true value. So, your conclusion of "less" and "decrease" is incorrect. It should be "greater" and "increase."