For each of the following changes, predict whether you would expect the %CH3COOH

Question

For each of the following changes, predict whether you would expect the %CH3COOH to come out higher, lower, or would remain about the same. Briefly explain your reasoning.
1) Two extra drops of phenolphthalein were added to the flask before titrating 2) The buret was not rinsed with NaOH solution before filling it with NaOH solution. 3) Twice as much distilled water was added to the Erlenmeyer flask before titrating. 4) The pipet used to transfer the vinegar to the Erlenmeyer flask was not dry. 5) After pipeting the vinegar into the flask, an hour passed before you titrated the sample. The purpose of this experiment was to determine the equilibrium constant of the reaction between iron (III) chloride (FeC13) and potassium thiocyanate (KSCN) through the use of spectrophotometry. Part A: Producing the calibration curve Part B: FInding the equilibrium concentraions

Explanation / Answer

I think the image does not correspond to the problem statement.

I might understand that the chemical equation you are asking is:

CH3COOH + NaOH ------------- CH3COONa + H20

And I assume that you know the quantity of NaOH (moles) and you are looking for the quantity of CH3COOH

1.The phenolphthalein is an indicator so the %CH3COOH is not supposed to change. Extra indicator doesn´t affect experiments

2.If the buret was not rinsed with NaOH you could put impurities to your solution. If your buret has water by the moment you make the experiment you could lower the concentration of NaOH (and the number of moles)

The phenolphtalein turns pink in a basic solution, when NaOH is neutralized this color apparently dissapears so if you dilute the NaOH, the number of moles decreases on a known ammount of volume so you would need less CH3COOH to neutralize the NaOH, by the time you make your calculations you will get less quantity of CH3COOH than you really need. So the CH3COOH is lower.

3.The CH3CCOH remains the same. The point of the tritation is is to match the base with an acid. Since you know the exact ammount of NaOH (moles and volume) you can easily match with the ammount of CH3COOH. You only need to get the number of moles of CH3COOH, you can measure the volume at any time so it doesn´t matter if you put more or less water in the flask.

4. The vinegar will be diluted so you will have fewer moles in the pipet and in flask. So in the tritation you will need less amount of NaOH to neutralize it so the CH3COOH will be fewer than real ammount.

5. The ammount of CH3COOH will remain the same, it should not change the results.

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