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Barium hydroxide is an alkali. It reacts with hydrochloric acid. How does the pH of the hydrochloric acid change as an excess of aqueous barium hydroxide is added?
(A) The pH decreases from pH 14 and becomes constant at pH 7.
(B) The pH decreases from pH 14 to about pH 1.
(C) The pH increases from pH 1 and becomes constant at pH 7.
(D) The pH increases from pH 1 to about pH 14.

Last updated date: 20th Jun 2024
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Hint: The pH is a kind of measuring scale used to determine the acidity, or basicity of an aqueous solution. It varied from the 1 to 14 depending upon their acid, and basic character. The pH 7 indicates that the solution is neutral.

Complete step by step answer:
-First, let us know the pH scale. The pH scale ranges from 1 to 14; solutions having pH less than 7 indicated to be acidic, pH 7 to be neutral, and pH greater than 7 to be basic in nature.
-As mentioned in the question, Barium hydroxide is an alkali, it means its pH range is greater than 7; whereas hydrochloric acid is a strong acid, its pH value is less than 7.
The reaction between acid and base is called neutralization reaction and produces salt and water on reaction. The reaction is mentioned below-
\[Ba{{(OH)}_{2}}+2HCl\to BaC{{l}_{2}}+2{{H}_{2}}O\]
-Now, when we will add the excess of aqueous barium hydroxide it will affect the pH of the solution.
-The addition of barium hydroxide first neutralize the acidic nature of HCl resulting in increase of pH till 7 and then after addition of excess of barium hydroxide will result in the increase of pH from 7 to 14
-On addition, the pH of Hydrochloric acid will increase from pH 1 to 14 which means that the solution will turn out to be basic in nature, and the effect of acid will reduce in the solution.

-In the last, we can conclude that the pH increases from pH 1 to about pH 14. The correct option is D.

Note: It should be noted that the above reaction is a kind of neutralization reaction. The reaction of which is mentioned below-
\[2HCl+Ba{{(OH)}_{2}}\to BaC{{l}_{2}}+2{{H}_{2}}O\]
Here, we can see from the balanced reaction that 2 moles of HCl is required to neutralize one mole of Barium Hydroxide. In the balanced neutralization reaction. Moles of ${{H}^{+}}$ ions from the acid=Moles of $O{{H}^{-}}$ ions from the base. This is also called the equivalence point where the number of moles of hydroxide ions is equal to the number of moles of hydrogen ions.