2. A 100.00 mL volumetric flask is loaded with 1.60 grams of NaF. To this was added 30.0 mL of a 4.00 M solution of HF. When this flask is filled to the mark and shaken to ensure complete mixing, what is the pH of the final solution

pH of the final solution = 3.8

Explanation:

Concentration of NaF = molar

                                    = 0.3 molar

NaF → Na⁺ +    F⁻

HF   ⇆ H⁺    +    F⁻

         according to common ion effect dissociation of weak acid decreases.

        Ka =

⇒    [H⁺]  = ...............(1)

{Ka of HF = 3.5 x 10⁻⁴} & Concentration of HF = 30 x 4 x 10⁻³ = 0.12 molar

from equation 1

⇒ [H⁺]  =     [Concentration of F⁻ ≡ Concentration of NaF]

⇒ [H⁺] = 0.00014

⇒pH = - log 0.00014 = 3.85

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error