Question

Imagine that you are attempting to determine the concentration of an acid by titration with a solution of sodium hydroxide with a known concentration, using phenolphthalein as an indicator. For each of the following sources of error, indicate whether the calculated concentration of acid would be too high or too low.

i. An air bubble was present in the tip of the buret before beginning the titration but was absent at the end of the titration.

ii. You added too much base and went beyond the end point.

iii. Some of the acid splashed on to the sides of the flask and wasn’t titrated.

Answer 1

i) If there were air bubbles at the start, and then during the titration, they floated up and popped, it would make it

look like you used more NaOH than you actually did, so the concentration should be high.

If there were air bubbles at the start, but they didn't float and pop, but remained the same, it shouldn't have much

effect on the concentraion (maybe a very slight effect due to the expansion of the bubble as the level of liquid

decreased - that would cause youconcentration to be slightly less since the expanded bubble would make it look

like there was more NaOH left in the burette than actually was) .

ii ) if we added too much base and went beyond the end point , means the concentration of base is increases and

your acid concentration is decreases.

therefore, ur actual acid concentration value is lower than the value u got.The concentration of acid, it will be low,

since u added excess bases to the solution, it will try to react with as many molecules of acid as possible, which

will lower the concentration of acid in the actual solution.

iii) The concentation of acid would decreases, because some of the acid splashed on sides of the flask, so that it

would not react with base. so very little amount of base is needed to get the end point of the reaction. so finally the

concentration of acid will decreases.