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Difficulty: EasypH and pOH Scale and Calculations

What is the pH of an aqueous solution containing 0.365 g dm−30.365\text{ g dm}^{-3} of hydrochloric acid (HCl\text{HCl})? [Molar mass of HCl=36.5 g mol−1\text{HCl} = 36.5\text{ g mol}^{-1}]

  1. 2.02.0Answer
  2. B
    12.012.0
  3. C
    0.440.44
  4. D
    1.01.0

Answer

The pH of the solution is 2.0.
The solution has a molar concentration of 0.01 mol dm−30.01\text{ mol dm}^{-3} (0.365 g dm−3/36.5 g mol−10.365\text{ g dm}^{-3} / 36.5\text{ g mol}^{-1}). Taking the negative base-10 logarithm of 1.0×10−2 mol dm−31.0 \times 10^{-2}\text{ mol dm}^{-3} yields a pH of 2.0.

Step-by-Step Solution

1
Convert mass concentration to molar concentration (molarity)
[HCl]=0.365 g dm−336.5 g mol−1=0.01 mol dm−3=1.0×10−2 mol dm−3[\text{HCl}] = \frac{0.365\text{ g dm}^{-3}}{36.5\text{ g mol}^{-1}} = 0.01\text{ mol dm}^{-3} = 1.0 \times 10^{-2}\text{ mol dm}^{-3}
pH calculations require concentration in units of mol dm−3\text{mol dm}^{-3}.
2
Determine the hydrogen ion concentration [H+][\text{H}^+]
[H+]=1.0×10−2 mol dm−3[\text{H}^+] = 1.0 \times 10^{-2}\text{ mol dm}^{-3}
Hydrochloric acid is a strong monoprotic acid that fully dissociates in water.
3
Calculate the pH using the pH formula
pH=−log⁡10[H+]=−log⁡10(1.0×10−2)=2.0\text{pH} = -\log_{10}[\text{H}^+] = -\log_{10}(1.0 \times 10^{-2}) = 2.0
pH is defined as the negative logarithm to base 10 of the hydrogen ion concentration.

Key Concept

Calculating pH from mass concentration of a strong acid
Estimated Time:1m 0s
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Topics

pH and pOH Scale and Calculations

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