Question

1) If the barometer reading is recorded to be higher than the actual value. What effect does this error have on the reported value of the molar mass of the compound compared to the true value? Briefly explain (Too High, Too low, Unchanged)

2) If the water bath only reached a temperature of 94.9C but you still used the value of 100C in the calculation what effect would this error have on the reported value for the molar mass of the compound as compared to the true value? Briefly explain (Too High, Too low, Unchanged)

3) A 250 mL Erlenmeyer flask has a measured volume of 287mL. The experiment is performed with a this flask but the volume of 250 mL is mistakenly used in the molar mass calculation. What effect does this error have on the reported value? Briefly explain (Too High, Too low, Unchanged)

4) When performing this experiment if your mistakenly added 6 mL of volatile liquid instead of 4 mL at the start. What effect would this have on the calculated value of the molar mass or the compound assuming you still heated until the liquid is gone? Briefly explain (Too High, Too low, Unchanged)

Answer 1

Part 1)

We have the ideal gas equation (Assuming that the compound obey ideal gas law)

PV =nRT = (w/M) RT      -------------- (1)

Where P is the pressure

V is the volume

n is the number of moles

w is the mass of the compound

M is the molecular mass of the compound

R is the universal gas constant

T is the temperature.

Here we can see that P (1 / M) (V, T and w being constant)

Here, since the pressure recorded is higher than the actual value, the molar mass calculated will be less than the actual value and therefore the error will be too low.

Part 2)

From equation 1

T M (Here, P, V, and w being constant)

Since the temperature is higher than the actual value, the calculated molar mass will be higher than the actual value and therefore, the error will be too high.

Part 3)

From equation 1

V (1 / M) (Here, P, T, and w being constant)}

Here, since the volume used is lower than the actual value, the calculated molar mass will be higher than the actual value and therefore, the error will be too high.

Part 4)

From equation 1

V   w        (P, T and M being constant)

Here, since the added volume is higher than the required volume, the mass of the compound will be higher than the actual mass but does not affect the value of the molar mass of the compound and therefore the error will be unchanged.