overshot titration in stock

You suspect that you overshot the endpoint of the titration (or added too much NaOH solution in your first attempt at titrating the KHP with NaOH.) Since the calculations are simple you go ahead and calculate the concentration of NaOH for this first titration along with the values for later titrations. When the concentration of your suspect (overshot) value is compared to the concentration values of the rest of your titrations what would you look for in the calculated concentration to confirm your suspicion of having overshot the end point?

In the chemistry laboratory, titration is a technique that is used to determine the concentration of a solution with an unknown concentration by carefully monitoring a reaction of that solution with a solution of known concentration.

5) In this simulated titration, the KHP solution was prepared for you and the precise concentration was given. Which of the following hypothetical errors would have a greater influence on the average NaOH concentration? Making a 1% mistake in preparing the original KHP solution, or overshooting the end point by 1% in one of your titrations?

2)if the NaOH has added to a flask with water in it, it should make a difference as you will still be placing the same number of moles in the flask for the titration.

Look up the pH indicator using the link in the Resources section if you are performing an acid-base titration. The pH indicator is a chemical that changes color over a given pH range. Before beginning your titration, you should have added a couple drops of the indicator, so you"ll already know which one you are using. The link under the Resources section will tell you what color change to expect when your titration is complete.

Swirl the flask of analyte while adding titrant from the buret. (The analyte is the chemical you are testing in the titration, while the titrant is the standard you are adding.) Swirling will make sure the analyte remains well-mixed so that the color change (when it occurs) is an accurate reflection of the pH of the solution.

Add titrant slowly. If you add titrant too quickly, you could easily overshoot the end point of your titration, at which point you may need to repeat the entire experiment.

Watch the solution closely for the color change. Once the solution begins to change color and the new color persists for at least 30 seconds, you have reached the end point of your titration.

Because of the significant importance of acids and bases in chemical and biological processes, it is often necessary to know their concentrations as accurately as possible. In order to accurately determine the concentration of a compound, typically chemists will perform a volumetric analysis in which they use highly precise glassware such as volumetric flasks, volumetric pipets, and burets. The process used to determine the concentration of a solution with very high accuracy is called standardizing a solution. To standardize an unknown solution, you react that solution with another solution whose concentration is already known very accurately, typically using an experimental technique known as a titration.

Although properly performing a titration experiment is necessary for standardizing a solution, the experiment will ultimately be useless if the experimenter does not know how to analyze the results. Whether using a pH meter or a chemical indicator, the purpose of performing a titration is to determine how much titrant is necessary to completely neutralize the analyte. With that information, the starting concentration of the known, and the balanced chemical equation, it will be possible to determine the concentration of the unknown.

Example. A student needed to standardize a sample of sodium hydroxide for use in another experiment. To perform the standardization, she planned to neutralize it with a sample of potassium hydrogen phthalate, a weak solid acid with the chemical formula HKC8H4O4. For her first trial, she dissolves 0.453 g of HKC8H4O4 in 15.00 mL of distilled water and then she uses a pH meter to accurately record how the pH changes after each small addition of the unknown sodium hydroxide. She generates an unformatted titration curve that looks like the figure shown below:

Since the moles of base have now been determined stoichiometrically and the volume of base has been found using the titration curve, the concentration of NaOH can now be calculated. Recall that molarity = moles/liter so the volume from the titration curve must be converted to liters (24.1 mL x 1L/1000 mL = 0.0241 L)

If the endpoint volume could not be easily determined from the experimental data, a Gran plot could be generated to fairly accurately find this value. The derivation of a Gran plot is a bit beyond the scope of this class, but essentially it is a graphical means of estimating the equivalence point volume of a titration using linear approximations of non-linear relationships, such as the one that exists between pH and titrant volume. An important caveat to the use of Gran plots is that these linear approximations are only valid near the endpoint. To generate a Gran plot for the titration of a base into an acid as in this example, the student should identify all of her data points 10% below her estimated equivalence point found from looking at the normal titration curve. In this case, she estimated the equivalence point to occur at 24.1 mL of base addition so she would take all of the data points from 21.69 mL of base added (90% of the perceived endpoint) up to 24.1 mL of base added. She would then take all of those volumes and multiply each of them by 10-pH where the pH in the exponent corresponds to the specific pH associated with each of those volumes. A plot of volume (on the x-axis) vs. volume x 10-pH (on the y-axis) should yield a linear graph. The x-intercept of that line tells you the Gran plot estimation of the equivalence point. If the student was titrating a strong acid into a weak base as you are doing in lab, the process would be the same except instead of plotting volume of base added vs. volume of base added x 10-pH, you would instead plot volume of acid added vs. volume of acid added x 10-pOH, where pOH = 14 – pH. A very good video illustrating how to generate a Gran plot in Excel can be found here.

If instead of a solid acid, the student used an acidic solution of known concentration, the calculations would be virtually identical, except she would calculate the moles of acid used by multiplying the volume used (in liters) by the concentration of the acid (in M). Once the moles of the known compound have been determined, the other calculations can be performed exactly as written. For more practice with titration calculations, please refer to this video.

26. Export the data by either wirelessly emailing it to yourself or connecting it to the Lab PC and opening the data in the LoggerPro program. You will need this data to generate a properly formatted titration curve for your lab report

27. Titrate two more samples of sodium carbonate. If your first titration gave an appropriate curve using the LaqQuest, you may complete these titrations using only visual cues from the indicator. You may use the final volume in the buret from the previous trial as the initial volume in the buret for the next one (in other words, don’t refill the buret between trials unless it is almost empty) but be sure to record both the amount of acid you start the titration with and the amount you end the titration with so you can calculate the volume of acid actually dispensed

4. Generate 1) a titration curve and 2) a Gran Plot of one of your trials. Use proper formatting. Label equivalence point(s) in both figures. Recall from the pre-lab reading that a good overview for how to do a Gran plot can be found here https://www.youtube.com/watch?v=xJ8UgdW-O8E however, you must use Va vs. Va x 10-pOH (recall that pOH = 14 – pH) (20 points)

. In other words, draw conclusions based on your data that answer the QOD (10pts). (Consider the following questions: Did you get the expected titration curve? Did you achieve the desired dilution concentration? How can you demonstrate statistically how well you performed the dilution?)

7. When conducting this experiment, the amount of water used to dissolve the sodium carbonate is never of concern; however the buret had to be rinsed with the experimental HCl solution prior to performing a titration for fear of excess water inside the buret. Explain why water added to the Na2CO3 has no effect on the data, whereas water added to the HCl solution may drastically affect the data (10pts).

8. When only using the indicator to track the progress of his experiment a student accidentally overshot the endpoint. How will this technique error affect the calculated concentration of the HCl? Be specific in your explanation (i.e. don’t just say more accurate, less accurate, or no effect)! (10pts)