Question

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

Answer 1

Hint: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:
 \[{\text{pH}} = - {\text{log}}\left[ {{H^ + }} \right]\]

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.
\[\therefore [{H^ + }]\] concentration will be \[{\text{1}}{{\text{0}}^{{\text{ - 6}}}}{\text{mol }}{{\text{L}}^{{\text{ - 1}}}}\].
We can say that for \[{\text{1L}}\] urine \[{\text{1}}{{\text{0}}^{{\text{ - 6}}}}{\text{}}\]moles of \[{{\mathbf{H}}^ + }\] ions are present.
$\therefore $ Using the unitary method we can conclude that when \[{\text{1}}{\text{.3L}}\] of urine is eliminated, then the moles of \[{{\mathbf{H}}^ + }\] ion eliminated will be \[1.3 \times {10^{ - 6}}\] .

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 \[{\text{1N}}\] the solution of the strong acid. The concentration of \[{\text{2N, 3N, 10N,}}\] etc. gives negative pH values.
A solution of an acid having very low concentration, say \[{\text{1}}{{\text{0}}^{{\text{ - 8}}}}{\text{N,}}\] shows a pH = 8 and hence should be basic, but actual pH value is less than 7.