Imagine that you are attempting to determine the concentration of an acid by tit
ID: 946348 • Letter: I
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 higher or lower than the true value. You added too much base and went beyond the end point. Explain your answer. Answers without explanation will not be given am credit. Some of the acid splashed on to the sides of the flask and was not titrated Explain your answer. Answers without explanation will not be given any credit.Explanation / Answer
1. Sodium Hydroxide: (NaOH) is used in many industries, mostly as a strong base.
2. Phenolphthalein: (C20H14O4) is often used as an indicator in acid–base titrations, and is a weak acid. the weak acid is colourless and its ion is bright pink.
Adding extra hydrogen ions shifts the position of equilibrium to the left, and turns the indicator colourless.
Adding hydroxide ions removes the hydrogen ions from the equilibrium which tips to the right to replace them - turning the indicator pink. When a base is added to the phenolphthalein, the molecule ions equilibrium shifts to the right, leading to more ionization as H+ ions are removed.
The half-way stage happens between pH 8 -10, lab tests says at pH 9.3. Since a mixture of pink and colourless is simply a paler pink, this is difficult to detect with any accuracy!
a)
There are several types of errors that can make titration result differ from the reality.
First, there is an intrinsic error of the method - end point is not identical with equivalence point and color changes of indicators are not instant. Reasons of this difference are discussed in details in the end point detection and acid-base titration end point detection sections.
In some cases excess of the titrant must be used as it is titrant color that signals end point. While this is also intrinsic characteristic of the method, it can be adjusted for by blind trials.
If you added too much strong base (NaOH) you will just see a pink colour this indicate that you surpass the equilibrium point so it will be a higher value.
b) Losing solution for a too vigorous swirling can end in liquid splashing from the titration flask before the end point had been reached. It may also happen that some titrant lands on the table instead of inside the flask. So it would be lower from true value