Multiple Choice
A solution containing aqueous HCl would most likely have which property at 25 °C?
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17. Acid and Base Equilibrium
pH of Strong Acids and Bases
Multiple Choice
Which statement best describes the behavior of a strong acid such as in water when calculating pH?
A
It does not change because strong acids are neutral in water.
B
It completely dissociates, so is approximately equal to the initial acid concentration.
C
It partially dissociates, so an equilibrium expression with must be used to find pH.
D
It produces directly, increasing pH above 7.
Verified step by step guidance1
Understand that a strong acid like HCl completely dissociates in water, meaning it breaks apart fully into H\+ and Cl\- ions.
Recognize that because of this complete dissociation, the concentration of H\+ ions in solution is approximately equal to the initial concentration of the acid added.
Recall that the pH is calculated using the formula \(\mathrm{pH} = -\log[\mathrm{H}^+]\), where \([\mathrm{H}^+]\) is the concentration of hydrogen ions.
Note that for strong acids, you do not need to use an equilibrium expression or the acid dissociation constant \(K_a\) because the dissociation is complete and no equilibrium is established.
Conclude that the correct description is that the strong acid completely dissociates, so \([\mathrm{H}^+]\) is approximately equal to the initial acid concentration, which directly determines the pH.
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