Problem: What mass of sodium hypochlorite, NaOCl (molar mass 74.5 g/mol), must be added to 250 mL of 0.60 M HClO (hypochlorous acid, Ka = 3.5 x 10-8), in order to produce a solution having a pH of 7.25?A. 3.1 gB. 9.2 gC. 4.5 gD. 7.0 gE. 1.3 g

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We’re being asked to calculate the mass of sodium hypochlorite, NaOCl (molar mass 74.5 g/mol), must be added to 250 mL of 0.60 M HClO (hypochlorous acid, Ka = 3.5 x 10-8), in order to produce a solution having a pH of 7.25


HClO is a weak acid (and based on the Bronsted-Lowry definition, an acid is a proton (H+) donor. Once HClO loses its proton, its conjugate base is formed).

    HClO(aq)     +  H2O(l)   ⇌    ClO-(aq)             +  H3O+(aq)
    (weak acid)            (base)         (conjugate base)    (conjugate acid)


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Problem Details

What mass of sodium hypochlorite, NaOCl (molar mass 74.5 g/mol), must be added to 250 mL of 0.60 M HClO (hypochlorous acid, Ka = 3.5 x 10-8), in order to produce a solution having a pH of 7.25?

A. 3.1 g

B. 9.2 g

C. 4.5 g

D. 7.0 g

E. 1.3 g