Be sure to answer all parts. The active agent in many hair bleaches is hydrogen

Question

Be sure to answer all parts. The active agent in many hair bleaches is hydrogen peroxide. The amount of H2O2 in 14.5g of hair bleach was determined by titration with a standard potassium permanganate solution: 2 MnO4(aq) + 5 H2O2(aq) + 6 H+(aq) 5 O2(g) + 2 Mn2+(aq) + 8 H2O(l) (a) For the titration, how many moles of MnO4 were required if 40.8 mL of 0.154 M KMnO4 was needed to reach the end point? Write your answer to the correct number of significant figures. Enter your answer in scientific notation. ______ × 10 mol MnO4 (b) How many moles of H2O2 were present in the 14.5 g sample of bleach? Write your answer to the correct number of significant figures. ____ mol H2O2

Explanation / Answer

a) Number of moles of substance in solution are calculated using the formula,

Number of moles = Molarity of solution x Volume of solution in L.

For KMnO4 solution we have

Molarity = 0.154 M and

Volume = 40.8 mL = 40.8 x 10–3 L …………(1 mL = 10–3L)

Hence,

Number of moles of KMnO4 = Molarity of KMnO4 x Volume of solution

Number of moles of KMnO4 = 0.154 x 40.8 x 10–3.

Number of moles of KMnO4 = 6.28 x 10–3 mol KMnO4.

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b) Number of moles are also defined as,

Number of moles = Given mass of substance/Molar mass of the same substance.

For H2O2 solution,

Given mass = 14.5 g

Molar mass of H2O2 = 34

Number of moles of H2O2 = Given mass of H2O2/Molar mass of H2O2

Number of moles of H2O2 = 14.5/34

Number of moles of H2O2 = 0.426 mol H2O2.

Number of moles of H2O2 = 4.26 x 10–1 mol H2O2.

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