A student is asked to prepare 100.0 mL of 1.000×10⁻² M Na2SO4(aq) to use in a precipitation experime — Equilibrium Chemistry Question
Problem Context
A student is asked to prepare 100.0 mL of 1.000×10⁻² M Na2SO4(aq) to use in a precipitation experiment. The student first weighs out 0.1420 g of solid Na2SO4.
Model Answer
±0.1 mg. One point is earned for correct answer.
Model Answer
Circle: 100 mL volumetric flask, distilled water, dropper. Mass of Na2SO4 is transferred to a 100 mL volumetric flask. Less than 100 mL of distilled water is added and the flask is swirled until dissolved. Distilled water is then added until the meniscus reaches the calibration mark, the last few mL added with a dropper. One point is earned for selection of items. One point is earned for essential steps.
Model Answer
BaSO4. The first to precipitate will be the salt whose Ksp is first exceeded by the ion product [M2+][SO4 2-] - the salt with the smallest Ksp. One point is earned for selection and explanation.
Model Answer
Circle electrode on the right (negative/cathode). Electrons flow out of the negative pole; these electrons combine with the metal ion at the electrode into which they flow: M2+ + 2e- → M. One point is earned for choice and justification. || Pb; it has the most positive reduction potential, so its ion is the most easily reduced. One point is earned for selection. One point is earned for explanation.