Question

1. A 45.0 mL solution contains 3.4 x 10-3 moles of H3O+. What is the pH of the solution?

HB- + H2O -> B2- + H3O+

2. 5.00 mL of the BTB stock solution will be used in all 5 of the solutions to be studied. Each of the five solutions are diluted to 50.00 mL total. What is the new concentration of BTB in the solutions?

Answer 1

Answer :

# of moles of H₃O⁺ = 3.4 x 10^-3. Volume of solution = 45.0 mL = 45.0 x 10^-3 L.

Let us calculate [H₃O⁺] in moles/L i.e Molar concentration of [H₃O⁺].

Molarity = # of moles / Volume of solution in L =

Molarity of [H₃O⁺] = (3.4 x 10^-3) / (45.0 x 10^-3) = 0.076 M.

Then by definition of pH,

pH = -log[H₃O⁺]

pH = -log(0.076)

pH = 1.12

pH of the given solution is 1.12.

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2) Initial concentration of BTB solution needed to be given.

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