Freezing point depression experiments has several possibilities for error. Brief

Question

Freezing point depression experiments has several possibilities for error. Briefly discuss the effect each of the following would have on the calculated molar mass of the unknown. Would the calculated value be higher, lower, or no different from the true molar mass of the unknown, and why?

a. The student did not get all of the unknown to dissolve.

b. The student did not thoroughly dry the test tube before adding the unknown.

c. Not add enough rock salt was added to the ice bath (1/3 ice, 1/3 water. 1/3 rock salt), so the ice bath temperature was approximately –1.0°C instead of -4C.

Explanation / Answer

a)

if not all salt is dissolved, then, the total moles of solute will not be 100% complete, therefore, the molality will be decrease / be lower than the required

therefore, the depression point will be LOWER than it actually is, i.e. it should hav ea higer decrease

b)

if it isn ot dried, then humidity will increase the mass of water, i.e. solvent

then, molality will decrease ( incorrectly) which implies a lower decrease in temperature

c)

the Tf will not achieve its minimum potential

therefore, dTf will be incorreclty claculated

dTf is lower, which implies Kf is lower (which of course is false)

Related Questions

Navigate

• Browse (All)
• Browse F
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.