I did a lab on vinegar and titration. The question asks..
In the titration of acetic acid and NaOH the use of the color indicator mandates that excess base be present to detect the reading endpoint. Will this cause the calculated and reported mass percent of acetic acid in vinegar to be too high or too low? Explain.
I understand that in order to see an endpoint there must be somewhat excess of base I am just confused on whether or not it'll be too low or high. I was thinking too low. But I'm not sure, help??
In actual practice you try to set these things up so that the amount of excess added is such a small amount (0.01-0.03 mL) that it doesn't affect the results AND if you run a blank at the same time that usually takes care of that problem. Technically, however, you must add a small excess. So mols added extra is M x L = mols NaOH. That translates to mols acetic acid extra and that means SLIGHTLY higher results in grams and percent. Usually that's not anything to get too excited about.
Well, when it comes to excess base, it can be a bit like having too much of a good thing. In this case, having excess base is actually a good thing because it helps us detect the endpoint of the titration. The endpoint is when all the acetic acid has reacted with the NaOH, and adding just a little bit more NaOH changes the indicator color.
Now, if we don't have enough base, the endpoint won't be reached, and we won't be able to accurately calculate the mass percent of acetic acid in vinegar. In other words, our result would be too low because we wouldn't be accounting for all the acetic acid present.
On the other hand, if we have too much base, the endpoint might be reached before adding all the NaOH required. In this case, our result would be too high because we would be assuming that more acetic acid was present than there actually was.
So, to answer your question, having excess base in the titration will likely cause the calculated and reported mass percent of acetic acid in vinegar to be too high since the endpoint will be reached before adding all the required NaOH. Hope that helps, and remember, excess base is like the extra frosting on a cupcake - it's a good thing!
When titrating acetic acid (CH3COOH) with sodium hydroxide (NaOH) using a color indicator, it is necessary to have excess base present to ensure that the endpoint is accurately detected. The endpoint is the point at which the reaction between the acid and base is complete.
In this case, the color indicator typically used is phenolphthalein, which undergoes a color change from colorless to pink at the endpoint of the reaction. The excess base ensures that there is no unreacted acid left, resulting in a full neutralization reaction and the appearance of the pink color.
Now, let's consider the effect of this excess base on the calculated and reported mass percent of acetic acid in vinegar. The mass percent of acetic acid is calculated based on the balanced equation of the reaction, which is:
CH3COOH + NaOH → CH3COONa + H2O
If there is insufficient base added, the reaction will not completely neutralize the acetic acid. As a result, the calculated mass percent of acetic acid in vinegar will be lower than the actual value because the molar ratio used in the calculation assumes complete reaction.
On the other hand, if there is excessive base added, the reaction will proceed beyond the endpoint and excess base will be present in the system. This excess base will be accounted for in the calculation of mass percent, resulting in a higher calculated value.
Therefore, in the given scenario, the calculated and reported mass percent of acetic acid in vinegar will be too high when excess base is present.
To determine whether the calculated and reported mass percent of acetic acid in vinegar will be too high or too low when excess base is present for the color indicator, we need to consider the reaction that takes place during the titration.
In this titration, acetic acid (CH3COOH) reacts with sodium hydroxide (NaOH) in a 1:1 ratio to produce water (H2O) and sodium acetate (CH3COONa):
CH3COOH + NaOH → H2O + CH3COONa
The endpoint of the titration is the point at which all the acetic acid has reacted with the sodium hydroxide, and any additional sodium hydroxide will remain in excess.
Now, let's consider the role of the color indicator. A color indicator, such as phenolphthalein, changes color when the solution becomes basic. In other words, it indicates the presence of excess base (sodium hydroxide) in the solution. This is necessary because it's difficult to determine precisely when all the acetic acid has reacted just by observing the solution. The color change helps to confirm that the endpoint has been reached.
With this understanding, we can answer the question.
If excess base is present to detect the endpoint, it means that some sodium hydroxide will remain unreacted after the titration. This excess base will contribute to the measured volume on the burette. Consequently, the volume of sodium hydroxide recorded will be greater than what was actually required to react with all the acetic acid.
Since the measured volume of sodium hydroxide will be higher than it should be, the calculation of the mass percent of acetic acid in vinegar will be based on a higher volume of sodium hydroxide. As a result, the calculated mass percent of acetic acid in the vinegar will be higher than the actual value.
In summary, when excess base is present to detect the endpoint in the titration of acetic acid and NaOH, the calculated and reported mass percent of acetic acid in vinegar will be too high.