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Question: Urine normally has a pH of \[{\mathbf{6}}.{\mathbf{0}}\] . A patient eliminates \[{\mathbf{1}}.{\mat...

Urine normally has a pH of 6.0{\mathbf{6}}.{\mathbf{0}} . A patient eliminates 1.3  litres{\mathbf{1}}.{\mathbf{3}}\;{\mathbf{litres}} of urine per day. How many moles of H+{{\mathbf{H}}^ + } ions does he eliminate in a day?
A.1.3×10−31.3 \times {10^{ - 3}}
B.1.3×10−61.3 \times {10^{ - 6}}
C.1.94N1.94{\text{N}}
D.1.94×10−2N1.94 \times {10^{ - 2}}{\text{N}}

Explanation

Solution

To answer this question, you should recall the concept of pH scale and the properties of acid and base. The pH scale is a logarithmic scale that is used to measure the acidity or the basicity of a substance. We shall calculate the concentration of hydrogen ions from the pH and use it to calculate the number of moles of hydrogen ion.
The formula used:
pH=−log[H+]{\text{pH}} = - {\text{log}}\left[ {{H^ + }} \right]

Complete step by step answer:
The possible values on the pH scale range from 0 to 14. The term pH is an abbreviation of potential for hydrogen. Acidic substances have pH values ranging from 1 to 7 and alkaline or basic substances have pH values ranging from 7 to 14. A perfectly neutral substance would have a pH of exactly 7. The pH of a substance can be expressed as the negative logarithm of the hydrogen ion concentration in that substance.
We are given the given urine sample as pH = 6.
∴[H+]\therefore [{H^ + }] concentration will be 10 - 6mol L - 1{\text{1}}{{\text{0}}^{{\text{ - 6}}}}{\text{mol }}{{\text{L}}^{{\text{ - 1}}}}.
We can say that for 1L{\text{1L}} urine 10 - 6{\text{1}}{{\text{0}}^{{\text{ - 6}}}}{\text{}}moles of H+{{\mathbf{H}}^ + } ions are present.
∴\therefore Using the unitary method we can conclude that when 1.3L{\text{1}}{\text{.3L}} of urine is eliminated, then the moles of H+{{\mathbf{H}}^ + } ion eliminated will be 1.3×10−61.3 \times {10^{ - 6}} .

Hence, the correct answer to this question is option B.

Note:
You should know about the limitations of pH Scale
pH values do not reflect directly the relative strength of acid or bases: A solution of pH = 1 has a hydrogen ion concentration 100 times that of a solution of pH = 3 (not three times).
pH value is zero for 1N{\text{1N}} the solution of the strong acid. The concentration of 2N, 3N, 10N,{\text{2N, 3N, 10N,}} etc. gives negative pH values.
A solution of an acid having very low concentration, say 10 - 8N,{\text{1}}{{\text{0}}^{{\text{ - 8}}}}{\text{N,}} shows a pH = 8 and hence should be basic, but actual pH value is less than 7.