Hydrogen peroxide (H2O2) behaves like an acid in water. It has a Ka value equal

Question

Hydrogen peroxide (H2O2) behaves like an acid in water. It has a Ka value equal to 1.778x 10-12. When sold in stores, solutions of H2O2 are often 3.00% H2O2 by mass. The solution also contains a small amount of phosphoric acid (0.001% by mass) which stabilizes the solution as hydrogen peroxide easily decomposes. Since both hydrogen peroxide and phosphoric acid behave like acids in water, both acids will contribute H+ ions to the solution. The Ka for phosphoric acid is equal to 7.2 x 10-3. (HINT: assume the density of the solution is 1.000 g/ml). The two reactions that you will need are given below: (8 pts) a.) Determine the concentration (M) of H2O2 and H3PO4 from their provided mass percents. Assume 1.00 L of solution (Hint, review how a mass % is determined

Explanation / Answer

Acid strength is determined by a competition of H2O and the conjugate base of the acid for H+ HClO3(aq) + H2O(l) = H3O+(aq) + ClO3 -(aq) acid base acid base HClO3 (acid) and ClO3 - (conjugate base) form a conjugate pair. H3O+ (acid) and H2O (conjugate base) form a conjugate pair. H2O(l) + NH3(aq) = NH4 +(aq) + OH-(aq) acid base acid base H2O (acid) and OH- (conjugate base) form a conjugate pair. NH4 + (acid) and NH3 (conjugate base) form a conjugate pair. H2O(l) + H2O(l) = H3O+(aq) + OH-(aq) acid base acid base H2O(l) = H+(aq) + OH-(aq) We can express this process of autoionization in terms of an equilibrium constant: Can assume that concentration of H2O remains constant and can be absorbed into equilibrium constant, Kw. [ ] [ ] + - 3 2 + - 2 2 3 2 H O OH H O H O OH H O w K K K ?? ?? ?? ?? = = = ?? ?? ?? ?? [ ] 2 -1 H O 1000g 1 55.

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