Question

Titration questions.
Answers are discussing the effect on measured molarity if said circumstances occur in a lab experiment.

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Summarized explanations are fine if you don't want to answer all the questions.
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Effects are listed as H (Higher), L (Lower) and N (Not affected) molarity.

1. The end point of the titration was overshot (H/L/N).
2. A drop of base was left adhering to the tip of the base buret. (H/L/N)
3. Some drops of acid were left clinging to the walls of the flask. (H/L/N)
4. The standard acid solution was obtained in a wet beaker. (H/L/N)
5. A wet flask was used for the titration. (H/L/N)
6. Instead of 2 drops, 4 drops of phenolphthalein were added. (H/L/N)

Answer 1

#1: I believe "overshot" refers to going over the required "end point" so the molarity would be lower as a result.

#2: I'm not really sure what this would do to the molarity since it's not in the actual thing being measured??

#3: Since the drops of the acid are still included in the volume that is used in the molarity calculation formula, the results would be off as the acid included with the titration is not the same volume as the total acid inside the flask.

#4: The wet beaker would dilute and lower the molarity of the acid before the experiment even started.

#5: The lab itself states that it doesn't matter if the titration beaker is wet.

#6: I'm not really sure what phenolphthalein even does besides indicate things with coloring... would it affect molarity?

Answer 2

tl;dr I only know any possible answers to #s 1, 3, 4 and 5

Answer 3

1. The end point of the titration was overshot (H/L/N).

#1: I believe "overshot" refers to going over the required "end point" so the molarity would be lower as a result.

If you add more base than needed then you do the calculations with that volume of base, then the molarity of the acid will be calculated higher than the real value
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2. A drop of base was left adhering to the tip of the base buret. (H/L/N)

#2: I'm not really sure what this would do to the molarity since it's not in the actual thing being measured??

Again similar than in #1 you meassured that drop of base as if this were in the titration flask, your volume of base will be higher and the molarity of the acid will be higher than the real value.


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3. Some drops of acid were left clinging to the walls of the flask. (H/L/N)

#3: Since the drops of the acid are still included in the volume that is used in the molarity calculation formula, the results would be off as the acid included with the titration is not the same volume as the total acid inside the flask.

then the cvolume of base used in the titration will be lower than the needed and the molarity of the acid will be calculated lower than the real value.

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4. The standard acid solution was obtained in a wet beaker. (H/L/N)

#4: The wet beaker would dilute and lower the molarity of the acid before the experiment even started.

then the concentration calculated for the acid will be lower than the realvalue
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5. A wet flask was used for the titration. (H/L/N)

#5: The lab itself states that it doesn't matter if the titration beaker is wet. OK
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6. Instead of 2 drops, 4 drops of phenolphthalein were added. (H/L/N)

#6: I'm not really sure what phenolphthalein even does besides indicate things with coloring... would it affect molarity?
too much phenolphtalein will need more base to change the color


There are several reasons, why one should not use too much indicator. Indicators are usually acids and bases and the measurement will be affected when dealing with significantly diluted systems. Also for a colour change you need approximately a 1:10 ratio of protonated vs unprotonated indicator. Using too much indicator will result in adding too much acid and base


Phenolphtalein is slightly acidic. It does affect titration because if you add too much, then it will alter the concentration of whichever solution you are adding it in. If you added it to the acid, it will cause that acid to be more acidic than you may have calculated. The effect of that on the titration is that afterwards when you are adding the base in the acid to find the end-point is that the end point will not be the true end-point since the pH of the acid is lower because of the indicator. The amount of base needed to add to the acid will be more so it can neutralize it and this while ruin your entire experiment since it will not be accurate. It will not have a large difference but it's still different.

http://chemistry.stackexchange.com/questions/15438/amount-of-phenolphthalein-required

Answer 4

Thank you very much for the detailed explanations! @cuanchi ☺