1. To determine the concentration of a solution of nitrous acid , a 125.0 -mL sa

Question

1. To determine the concentration of a solution of nitrous acid, a 125.0-mL sample is placed in a flask and titrated with a 0.1335 M solution of sodium hydroxide. A volume of 30.59 mL is required to reach the phenolphthalein endpoint. Calculate the concentration of nitrous acid in the original sample.

_____ M

2. Potassium permanganate in acidic solution is used to titrate a solution of tin(II) ions, with which it reacts according to

A potassium permanganate solution is prepared by dissolving 16.02 g of KMnO4 in water and diluting to a total volume of 1.000 L. A total of 22.77 mL of this solution is required to reach the endpoint in a titration of a 100.0-mL sample containing Sn2+(aq). Determine the concentration of Sn2+ in the original solution.

______ M

Explanation / Answer

Q1.

HNO2

V = 125 mL

M = 0.1335 M of NaOH

V = 30.59 mL of base required

Find initial concentration

so..

HNO2 + NaOH = H2O + NaNO2

so

ratio is 1:1

mol of acid = ?

mol of base = MV= 0.1335*30.59 = 4.083765 mmol of OH- used

so

mmol of acid = 4.083765 mmol

so

[Acid] = mmol/V = 4.083765/125

[HNO2] = 0.032670 M

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