Question

What is the pH of 1M HCl?
A.0
B.1
C.2
D.3

Answer 1

Hint:pH is mathematically equal to the negative logarithm of hydrogen ion concentration present in the given solution. A strong acid like hydrochloric acid or strong base like sodium hydroxide completely dissociate into their respective ions in the solution.
Formula Used:
 \[{\text{pH}} = - {\text{log}}\left[ {{{\text{H}}^ + }} \right] = {\text{log}}\dfrac{1}{{\left[ {{{\text{H}}^ + }} \right]}}\]

Complete step by step answer:
The pH scale was given by Sorenson. It is a scale used to measure strength of an acid and a base. It is equal to negative logarithm of hydrogen ion concentration in the given solution, \[{\text{pH}} = - {\text{log}}\left[ {{{\text{H}}^ + }} \right] = {\text{log}}\dfrac{1}{{\left[ {{{\text{H}}^ + }} \right]}}\] .
For example, if a solution contains hydrogen ion concentration equals to \[{10^{ - 3}}{\text{M}}\] then its pH can be given as: \[{\text{pH}} = - {\text{log}}\left[ {{{10}^{ - 3}}} \right] = 3\] . The solution having pH value greater than 7 are basic and solutions having pH value less than 7 are acidic solutions. Neutral solutions have pH equals to 7. Similarly, pOH of a solution is used to determine strength of an acid and a base. It is equal to negative logarithm of hydroxide ion concentration present in the given solution,
 \[{\text{pOH}} = - {\text{log}}\left[ {{\text{O}}{{\text{H}}^ - }} \right]\] . The solution having pOH less than 7 are basic and greater than 7 are acidic solutions. Neutral solutions have pOH equal to 7.
As 1M HCl solution will have 1M hydrogen ion concentration as hydrochloric acid is a strong acid and it will get completely dissociate into its respective ions in the solution as follow:
 \[{\text{HC}}{{\text{l}}_{\left( {{\text{aq}}} \right)}} \to {\text{H}}_{\left( {{\text{aq}}} \right)}^ + + {\text{Cl}}_{\left( {{\text{aq}}} \right)}^ - \] .
Now, as we have 1M Hydrogen ion concentration in the solution, its pH can be given as: \[{\text{pH}} = - {\text{log}}\left[ 1 \right] = 0\] and thereby pH of 1M Hydrochloric acid solution will have pH equal to zero.

Thus, the correct option is A.
Note:
For a given solution, the sum of its pH and pOH is equal to 14. The base value of logarithm used in the equation of pH and pOH has a value of 10. Value of dissociation constant is defined for weak acid and weak base which tells about how much part of weak acid and weak base dissociates in the solution.