Question

Standardized NaOH solutions are typically restandardized if left unused for more than a week or two. The main concern is exposure to the atmosphere (thus it is important to seal the bottle well each time, and not leave it open during a lab period). Why is exposure to the atmosphere a concern (be specific)?

If a titration net volume should be 20.00 mL and a student accidentally goes one drop past this endpoint (~0.05 mL), what will the percent error in this titration be?

If the incorrect titration net volume described in question 3 is used to standardize an NaOH solution, will the calculated [NaOH] be higher or lower than the true value of that solution’s concentration? Explain briefly.

Answer 1

Sodium hydroxide reacts quickly with carbon dioxide to produce sodium carbonate.

We know that at end-point:

Then:

Then, after adding 0,05mL

The percent error will be:

You can see the normality of the base is directly proportional to the volume of acid.

After adding 0.05, the normality will be higher.

Also, from the definition of normaility

You can see normality is directly proportional to molarity or concentration. So, the concentration [NaOH] will be higher.