Determining Original Concentration of Nitrous Acid (HNO₂) Through Titration

How can we determine the original concentration of nitrous acid (HNO₂) through titration?

25.0 mL of nitrous acid (HNO₂) is titrated with a 1.235 M solution of KOH. The equivalence point (stoichiometric point) is observed after 9.26 mL of base is added. What is the original concentration of the acid?

Answer:

0.456 M

To determine the original concentration of nitrous acid (HNO₂) through titration, we first need to write the balanced neutralization equation for the reaction between nitrous acid and potassium hydroxide (KOH):

HNO₂ + KOH ⇒ KNO₂ + H₂O

Next, we calculate the reacting moles of KOH used in the titration:

9.26 mL of 1.235 M KOH react.

0.00926 L × 1.235 mol/L = 0.0114 mol

Then, we determine the reacting moles of nitrous acid (HNO₂) based on the balanced equation:

The molar ratio of nitrous acid to KOH is 1:1.

The reacting moles of HNO₂ are 1/1 × 0.0114 mol = 0.0114 mol

Finally, we calculate the initial concentration of nitrous acid (HNO₂) in the solution:

0.0114 moles of nitrous acid (HNO₂) are in 25.0 mL of solution.

[HNO₂] = 0.0114 mol / 0.0250 L = 0.456 M

Therefore, the original concentration of nitrous acid (HNO₂) in the solution is 0.456 M.