"Published in Newark, California, USA"
In standardizing a solution of NaOH against 1.431 grams of potassium hydrogen phthalate, C8H5KO4 (KHP), the analyst uses 35.50 mL of the alkali and has to run back with 8.25 mL of acid (1 mL = 10.75 mg NaOH). What is the molarity of the NaOH solution?
Solution:
The given word problem is about volumetric analysis problem because it involve the titration of samples and solutions. Potassium hydrogen phthalate (KHP) is a sample used to standardize the basic or alkali solutions that are prepared in the lab.
If NaOH solution is used to titrate KHP sample, then the chemical reaction for neutralization is
The concentration of NaOH solution used to titrate a sample of KHP is
Since, there's a back titration with an acid solution especially if there's an over titration with an alkali solution, then the above equation becomes
Usually, we put the indicator at the sample solution so that we know that we used the right amount of acid or alkali solution by its color. The color of the indicator is changed once it reached its end point. How about if you used the excess solution for titration, then we have to do the back titration until we get the correct color for its end point.
Therefore, the concentration of NaOH solution used to titrate a sample of KHP is
