Why is it important to the NaOH solution each time before you use it? Would it b

Question

Why is it important to the NaOH solution each time before you use it? Would it be better to use an unknown acid sample of a size that should require 10.000 ml or one that would require of the. Explain What effect on the molar mass of the unknown acid would each of the following have-that is-would it make the calculated molar mass high, low, or would have no effect. Adding 5 drops of phenolphthalein instead of 1 drop. Using a standard NaOH solution that has been left unstoppered for several days. Explain: Failing to remove an air bubble in the tip of the buret containing the NaOH solution prior to titration Failing to rinse down the unknown acid solution from the inside walls of the flask near the end of the titration Placing the unknown acid in a wet container prior to weight it

Explanation / Answer

A 1) It is important to swirl the NaOH solution every time we use, because the concentration is not uniform, in order to make the concentration of the solution uniform it is necessary to swirl the solution.

NaOH can absorb carbon dioxide from atmosphere and form sodium carbonate, it can also react with ions preent in water to form their hydroxides which will settle in the bottom over the period of time so the solution may not be uniform, hence it is necessary to swirl the solution each time we use.

A 2) There are number of acids available from monobasic to tribasic acid( HCl, H2SO4, HNO3, H3PO4) and from strong acid to dilute acid( CH3COOH, H2SO4) also the molarity of solution also vary with degrees of dilution. Moreover in order to determine the molarity of unknown base standard solution of acid is required. If large quantity of concentrated acid is present the reaction could be exothermic leading to accidents.

B

1. Phenolpthalein also contains acidic group which reacts with base leading to structural change to benzenoid form which is pink in colour. when excess of phenolpthalein is used it will react with base which increases the burette reading.

2. standard NaOH left unstoppered for several days can absorb carbon dioxide from atmosphere and form sodium carbonate which changes the molarity of the solution and hence decreases the molarity.

3. Air in the tip of burette will add to the reading and hence reading will be higher than the normal.

4. as the unknown acid solution from the inside wall of the flask does not undergo titration the reading will be lower than expected.

5. Unknown acid in wet container may absorb moisture from the container which may lead to change or decrease concentration of the acid

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