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Question #44653

Difficulty: 8/10 | 🟢 Free

The Question

Hydrogen sulfide (\ce{H2S}) is a toxic gas. Its Henry's law constant (KHK_H) in water at 298 K298 \text{ K} is 1.5×108 Pa1.5 \times 10^8 \text{ Pa}. If the partial pressure of \ce{H2S} over an aqueous solution is 5.20×102 Torr5.20 \times 10^2 \text{ Torr}, determine the molality of \ce{H2S} in the solution. (Assume ideal behavior and report your answer adhering strictly to the rules of significant figures).

Options

  • A.

    2.6×10−2 mol kg−12.6 \times 10^{-2} \text{ mol kg}^{-1}

  • B.

    2.57×10−2 mol kg−12.57 \times 10^{-2} \text{ mol kg}^{-1}

  • C.

    2.5×10−2 mol kg−12.5 \times 10^{-2} \text{ mol kg}^{-1}

  • D.

    4.6×10−4 mol kg−14.6 \times 10^{-4} \text{ mol kg}^{-1}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

Significant Figures in Arithmetic|Henry’s Law Constant (Kh) Trends

Why This Question Is Tricky

Common Mistakes

This question tests the strict application of significant figures in physical chemistry calculations, specifically the 'weakest link' rule in multiplication/division.

Students often ignore the sig-figs of empirically given constants (like KHK_H) and default to 3 sig-figs, leading to the trap answer 2.57×10−22.57 \times 10^{-2}.

Additionally, it traps students who use the approximation 1 atm≈105 Pa1 \text{ atm} \approx 10^5 \text{ Pa} instead of the exact 101325 Pa101325 \text{ Pa}, which shifts the unrounded value to 0.02530.0253, rounding incorrectly to 2.5×10−22.5 \times 10^{-2}.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterSome Basic Concepts of Chemistry - Class 11 Part 1
ConceptSignificant Figures in Arithmetic
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree