A 1.00 liter solution contains 0.43 M hydrofluoric acid and 0.56 M potassium fluoride. If 0.280 moles of potassium hydroxide are added to this system, indicate whether the following statements are true or false. (Assume that the volume does not change upon the addition of potassium hydroxide.) A. The number of moles of HF will increase. B. The number of moles of F- will decrease. C. The equilibrium concentration of H3O will increase. D. The pH will decrease. E. The ratio of [HF] / [F-] will remain the same.

Answers are in the explanation

Explanation:

Equlibrium of HF in H₂O is:

HF + H₂O ⇄ F⁻ + H₃O⁺

Now, the KOH reacts with HF, thus:

KOH + HF →  F⁻ + H₂O

That means after reaction, concentration of HF decrease increasing F⁻ concentration.

Now, seeing the equilibrium, as moles of HF decrease and F⁻ moles increase, the equilibrium will shift to the left decreasing H₃O⁺ concentration.

For the statements:

A. The number of moles of HF will increase. FALSE. HF react with KOH, thus, moles of HF decrease

B. The number of moles of F- will decrease. FALSE. The reaction produce  F⁻ increasing its moles.

C. The equilibrium concentration of H₃O⁺ will increase. FALSE. The equilibrium shift to the left decreasing concentration of H₃O⁺

D. The pH will decrease. FALSE. As the H₃O⁺ concentration decrease, pH will increase

E. The ratio of [HF] / [F-] will remain the same. FALSE. Because moles of HF are decreasing whereas F- moles are increasing changing, thus, ratio.

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