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These 10 free Quantitative Lab Skills I questions are organized by exam domain, so you can see how each part of the BCSI Quantitative Lab Skills I blueprint is tested. Reveal the answer and explanation under each question.
A measured reagent mass is recorded as 0.00004080 g. The analytical report requires normalized scientific notation without changing the unit or the precision recorded. Which entry belongs in the report?
Correct answer: B - 4.080 × 10^-5 g
A technician prepares a v/v solution using the specified volume of pure liquid solute and brings the mixture to the required final volume. The solvent volume used is less than 'final volume minus solute volume.' All other preparation checks pass. How should this discrepancy be assessed?
Correct answer: C - Accept it; the specified solute and final volumes were achieved.
A vessel already contains 180.0 g of water. A technician must add a pure, nonreactive solute to obtain a 10.0% w/w solution without removing water. Assume complete dissolution and no material loss. What mass of solute is needed?
Correct answer: A - 20.0 g
The mass percentage of a nonreactive solute was calculated from the recorded masses of solute and water added. The solute dissolved completely. Which later observation would invalidate that concentration calculation?
Correct answer: D - Some water evaporated before the preparation was completed.
A worksheet converts a measured mass from grams to milligrams using 1 g = 1,000 mg. A reviewer wants to limit the result to one significant figure because the conversion factor is written as 1,000. Which principle resolves the disagreement?
Correct answer: B - The defined conversion is exact; the measured mass limits the precision.
An analyst obtains a dry solute's mass by subtracting the empty weighing vessel's mass from the mass of vessel plus solute. All the solute is then transferred into a solution of measured final volume. When dividing solute mass by solution volume, which reporting approach respects both operations?
Correct answer: C - Apply the decimal-place rule to the subtraction, then the significant-figure rule to the quotient.
A glucose preparation is specified by its molality, in mol/kg. A trainee plans to dissolve the glucose and add water to a volumetric flask's calibration mark. To meet the stated concentration basis, the preparation instead needs to control:
Correct answer: D - The mass of water used as the solvent.
A solution warms and its volume increases. Its solute amount and solvent mass remain unchanged. At the higher temperature, how do its molarity and molality compare with their original values?
Correct answer: D - Molarity is lower; molality is unchanged.
A laboratory needs 250.0 mL of 0.0800 mol/L CuSO4. The available solid is pure CuSO4·5H2O, with a molar mass of 249.69 g/mol; each mole of this hydrate supplies one mole of CuSO4. What mass should be weighed for the final solution?
Correct answer: A - 4.99 g
A reagent has a nominal target of 0.200 mol/L and an accepted release interval of 0.196-0.204 mol/L. A valid assay gives 0.201 mol/L. Every other release requirement has been met, and the authorized technician must select the disposition. What follows from these results?
Correct answer: A - Release the reagent; its concentration meets the specification.
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