If the end point in the titration of oxalic acid with NaOH solution is super-passed (too pink), will the molar concentration of NaOH be hiegher or lower than the actual value ? Explain ..
H2C2O4 + 2NaOH ==> Na2C2O4 + 2H2O
eqn 1. moles H2C2O4 = grams/molar mass
eqn 2. moles NaOH = 2 x moles H2C2O4
eqn 3. M NaOH = moles NaOH/L NaOH
eqn 1 doesn't change.
eqn 2 doesn't change.
eqn 3 changes. If L NaOH is too high, then M NaOH is too low.
If the endpoint in the titration of oxalic acid with NaOH solution is super-passed, meaning that the solution turns more pink than the expected endpoint color, it indicates that excessive NaOH has been added to neutralize the oxalic acid.
In this case, the molar concentration of NaOH will be higher than the actual value. This is because the endpoint is determined based on the stoichiometry of the reaction, where an equal amount of moles of oxalic acid and NaOH react to form a salt and water. However, if excess NaOH is added, it means that more moles of NaOH were used to neutralize the same amount of oxalic acid. This results in a higher concentration of NaOH than what would have been needed for the complete neutralization.
Therefore, the molar concentration of NaOH will be higher than the actual value if the endpoint is super-passed in the titration of oxalic acid with NaOH solution.
If the endpoint in the titration of oxalic acid with NaOH solution is overshot or if the solution becomes too pink, it means that excess NaOH has been added beyond the stoichiometric equivalence point. In this case, the molar concentration of NaOH will appear to be higher than the actual value.
To understand why this happens, let's look at the titration reaction between oxalic acid (H2C2O4) and sodium hydroxide (NaOH):
H2C2O4 + 2NaOH -> Na2C2O4 + 2H2O
In the titration, the goal is to add a known volume of the NaOH solution (with a known concentration) to completely neutralize the oxalic acid. The stoichiometric equivalence point occurs when the moles of NaOH added are exactly equal to the moles of oxalic acid. At this point, all of the oxalic acid has reacted, and any additional NaOH added will be in excess.
However, if the endpoint is overshot, it means that too much NaOH has been added. The excess NaOH reacts with the indicator used in the titration, causing the solution to turn pink or persistently pink, even though the reaction should have already reached the stoichiometric equivalence point.
So, when the endpoint is overshot, it falsely indicates that more oxalic acid has been neutralized than what actually occurred. As a result, the calculated molar concentration of NaOH will appear to be higher because the volume of excess NaOH is included in the calculation but should not have been.
To avoid this issue, it is important to carefully add the NaOH solution drop by drop near the endpoint, ensuring that you stop as soon as a faint permanent pink color appears and does not intensify further.