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StoichiometryMCQ

Given that the density of Hg(l) at 0°C is about 14 g mL-1, which of the following is closest to the Stoichiometry Chemistry Question

Question

Given that the density of Hg(l) at 0°C is about 14 g mL-1, which of the following is closest to the volume of one mole of Hg(l) at this temperature?

A.

0.070 mL

B.

0.14 mL

C.

1.4 mL

D.

14 mL

✓ Correct
E.

28 mL

💡 Solution & Explanation

STEPS:
1. Identify the formula relating density, mass, and volume: Density (DD) is defined as mass (mm) divided by volume (VV):
D=mVD = \frac{m}{V}
Rearranging this formula to solve for volume yields:
V=mDV = \frac{m}{D}
2. Find the molar mass of Mercury (Hg): Liquid mercury (Hg(l)\text{Hg}(l)) has a molar mass of approximately 200.59 g mol1200.59\text{ g mol}^{-1}, which can be found on the periodic table included in the exam booklet. For a quick mental estimation on Section I—where calculators are not permitted—this value can be rounded to 200. g mol1200.\text{ g mol}^{-1}.
3. Calculate the mass of exactly one mole of Hg(l)\text{Hg}(l):
Mass of 1 mole of Hg=1 mol×200. g mol1=200. g\text{Mass of 1 mole of Hg} = 1\text{ mol} \times 200.\text{ g mol}^{-1} = 200.\text{ g}
4. Calculate the volume of one mole of Hg(l)\text{Hg}(l): Substitute the estimated mass (200. g200.\text{ g}) and the given density (14 g mL114\text{ g mL}^{-1}) into our rearranged density equation:
V=200. g14 g mL1=1007 mL14.3 mLV = \frac{200.\text{ g}}{14\text{ g mL}^{-1}} = \frac{100}{7}\text{ mL} \approx \mathbf{14.3\text{ mL}}
This estimated volume is closest to 14 mL, which corresponds to Option D.

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WHY_OTHERS_WRONG:
*
A is incorrect: 0.070 mL0.070\text{ mL} is obtained if a student mistakenly inverts the volume calculation and divides the density by the mass (14200=0.070\frac{14}{200} = 0.070) instead of dividing the mass by the density.
*
B is incorrect: 0.14 mL0.14\text{ mL} represents a decimal place-value error during division, or is the result of using an incorrect value for the molar mass of mercury (such as its atomic number, 80).
*
C is incorrect: 1.4 mL1.4\text{ mL} is off by a factor of 10, which typically occurs due to a decimal-shifting mistake during long division (e.g., incorrectly writing the decimal point when dividing 200 by 14).
*
E is incorrect: 28 mL28\text{ mL} is double the correct volume, which could occur if a student mistakenly assumed that mercury exists as a diatomic molecule (such as Hg2\text{Hg}_2) under these conditions or made a multiplication error during division.

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