A sample of potassium hydrogen iodate, (KH(IO3)2), which is an acid, with a mass

Question

A sample of potassium hydrogen iodate, (KH(IO3)2), which is an acid, with a mass of 0.3471 g is dissolved in water and used to standardize a solution of magnesium hydroxide. An endpoint is reached when 32.14 mL of magnesium hydroxide has been added. Determine the molarity (in mol/L) of the magnesium hydroxide solution.

The standardized magnesium hydroxide solution is then used to titrate 49.14 mL of a solution of phenylammonium chloride (C6H5NH3Cl). An endpoint is reached when 39.76 mL of magnesium hydroxide has been added. Determine the molarity (in mol/L) of the phenylammonium chloride solution

Explanation / Answer

(1) 2 KH(IO3)2 + Mg(OH)2 => 2 KIO3 + Mg(IO3)2 + 2 H2O

Moles of KH(IO3)2 = mass/molar mass of KH(IO3)2

= 0.3471/389.92 = 0.00089018 mol


Moles of Mg(OH)2 = 1/2 x moles of KH(IO3)2

= 1/2 x 0.00089018 = 0.00044509 mol


Molarity of Mg(OH)2 = moles/volume of Mg(OH)2

= 0.00044509/0.03214 = 0.01385 mol/L


(2) Mg(OH)2 + 2 C6H5NH3Cl => MgCl2 + 2 C6H5NH2 + 2 H2O

Moles of Mg(OH)2 = volume x concentration of Mg(OH)2

= 39.76/1000 x 0.01385 = 0.00055062 mol


Moles of C6H5NH3Cl = 2 x moles of Mg(OH)2

= 2 x 0.00055062 = 0.0011012 mol


Molarity of C6H5NH3Cl = moles/volume of C6H5NH3Cl

= 0.0011012/0.04914 = 0.02241 mol/L

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