Question

A stoppered vaccumm flask contains 7.5 mL of .906 M H2O2 and 10 mL H2O. The syringe holds 7.5 mL of 1.00 M KI.

a. What is the initial concentration of H2O2 in the reaction flask after all reactants are combined?

b. What is the initial concentration of KI in the reaction flask after all reactants are combined?

c. What is the final concentration of H2O2 in the reaction flask after the reaction is complete?

d. What is the final concentration of KI in the reaction flask after the reaction is complete?

e. What would be suitable quantities of .906 M H2O2, H2O, and 1.00 M KI to use in order determine the order of reaction in respect to [KI]?

Answer 1

Total volume of reaction mixture = 7.5 + 10 + 7.5

= 25.0 mL

Moles of H2O2 added = 0.906 M * 7.5 ml = 6.795 mmoles.

Concentration of H2O2 in reaction mixture

= (0.906 M * 7.5 ml)/25 ml

= 0.272 M

Answer b)

Moles of KI added = (1.00 M*7.5 ml) = 7.5 mmoles

Concentration of KI = (1.00 M*7.5 ml)/25 ml

= 0.300 M

Answer c)

Equation involved is.

H2O2 + 2KI -----> I2 + 2KOH

1 mol of H2O2 react with 2 moles of KI

6.795 mole of H2O2 will react with 2*6.795 mol i.e. 13.59 mol of KI

Hence, KI is limiting, so, moles of H2O2 used = 1/2*(moles of KI) = 1/2*(7.5 mmol) = 3.75 mmol

Moles of H2O2 remaining = 6.795 - 3.75 = 3.045 mmol

Concentration of H2O2 after reaction = 3.045 mmol/25 ml = 0.122 M

d) After completion of reaction, whole of KI will be used up as it was limiting reagent.