please help 2. Assume that you failed to clean some grease off of your crucible

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please help

2. Assume that you failed to clean some grease off of your crucible before doing the percent water determination. If that grease then burned off during the determi- nation, explain how the percent water you calculated would be affected (ie., too low, too high, no effect). Be specific. Explain how each of the following would affect the percent sulfate you calculated, i.e., too low, too high, no effect. Be specific. 3. a. You added 15 mL (instead of 10 mL) of 0.25 M BaCI, to your unknown. You were in a hurry to get out of lab, so you did not rinse the last traces of solid BaSO, from the reaction beaker into the funnel. b.

Explanation / Answer

Ans. #2. Initial hydrated mass = Mass of crucible + Grease + Sample

Final dried mass = Mass of crucible + Sample

During the process of drying the hydrated sample, water is lost. Note that the grease is also burnt off and lost.

So, the net loss in mass = Mass of water + Mass of grease

# Since amount of water in hydrated sample is taken as the mass lost during drying, the observed amount of water in sample would be too high because the loss in mass also includes the mass of grease.

#3a. Balanced reaction:       K2SO4(aq) + BaCl2(aq) -------> BaSO4(s) + 2 KCl (aq)

            Or,      SO42-(aq) + Ba2+(aq) -------> BaSO4(s)

% sulfate is calculated in form of BaSO4 precipitated, above is shown the balanced equation for the same.

During the process, the moles of Ba2+ (from BaCl2) added must be equal to or greater than that of the SO42- in the sample.

# Suppose 10.0 mL BaCl2 solution is just sufficient to precipitate all the sulfate ion.

When you add 15.0 mL BaCl2 solution, there number of moles of precipitate of BaSO4 remains the same because all SO42- would have already been precipitated at 10.0 mL, after which there would be no sulfate ion remaining in the solution.

So, irrespective of the excess BaCl2 solution added, the mass of precipitate remains the same.

# Therefore, adding excess BaCl2 has no effect because it would not increase the mass of precipitate.

#3b. Presence of traces of BaSO4 from previous experiment would increase the total mass of BaSO4 precipitate collected at the end of this experiment.

Therefore, the net mass of precipitate obtained would be greater than the actual value because of mass of precipitate from previous experiment.

Therefore, observed mass and % sulfate would be too high compared to the actual one.

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