I. Prepare a standard solution of sodium hydroxide
II. Standardize a sodium hydroxide solution by using potassium hydrogen phthalate (KHP)
III. When given whether the acid is monoprotic, diprotic, or triprotic , determine the molar mass of the unknown organic acid.
IV. Calculate the Molarity of the Soft drink.
* 50 mL Buret
* Erlenmeyer Flask
* Sodium Hydroxide
* Unknown Acids (A, B, C)
* Soft Drink (Ginger Ale)
A Preparation of NaOH (standard solution)
1. With portions of water, rinse a 2L bottle.
2. To make 2L of a 0.1M solution, determine the amount of grams of sodium hydroxide that are needed and then weigh out the correct number of grams when showing the calculation.
3. To a container that is ½ to 1/3 full of water, add the pellets of sodium hydroxide. Shake to mix or speed up the dissolving of the pellets and fill to the top with water. Label your container with your name and date.
B Standardization of NaOH (Determine the actual concentration of the standard solution) 1. Drain the 50 mL buret and remember to fill the buret with water at the end of each lab.
2. To rinse the inside of the buret, pour a small amount of NaOH into it. Drain the buret through the stop cock. Rinse the buret more than once. (Remember to do this before you start th lab experiment to clean the buret.)
3. Fill the buret with the NaOH solution and to remove any air, allow a small quantity to pass through the stopcock.
4. Rinse a 250 mL Erlenmeyer flask and then make sure the bottom of the flask is dry. To get the mass of only the solute, rezero the flask on the scale.
5. Add about 0.20 to 0.30 grams of KHP (acid) to the flask. Measure precisely to the 100ths place and record the mass. Add approximately 60-70 mL of water to dissolve KHP and add 2-3 drops of phenolphthalein indicator. Shake or swirl the flask to speed up the dissolving of the KHP.
6. Record the level of NaOH in the buret (to the 100ths Place). All volumes should be to the 100ths place (0.00). Carefully add the NaOH to the flask containing the acid solution. Throughout the experiment, rinse the inside of the flask with water from a water bottle and stop adding NaOH and then swirl the flask to mix the solution.
7. Stop adding NaOH when a light pink color persists (when neutralization occurs). Record the final reading of NaOH thats in the buret and find the final volume.
8. Calculate the molarity of the NaOH solution and then complete all 12 titrations before beginning to solve the calculations. Expand your calculations to 4 decimal places and accept only the values that are within 0.005 of each other.
9. Of the accepted molarity readings, take the average. This is known as the molarity of your standardized base solution, which will be used to calculate the molar masses of the unknown acids and molarity of a soft drink. C Calculating the Molar Masses of Unknown Acids
1. Repeat the same steps 1-4 from Section B to prepare for the titration of the unknown acid solution. 2. Repeat the same steps 5-7 substituting the unknown acid for KHP. The unknown acids are in labeled jars A, B, and C. It will be indicated whether the acids are monoprotic, diprotic, or triprotic. 10 titrations should be completed for each unknown acid. 3. From the equation on the first page, calculate the molar mass of the acid using your average molarity. Find the molar mass based on the number of protons in each acid. 4. Accept the values that are within 1.0 of each other. Calculate the average of all the acceptable values and then repeat for the remaining acids. 5. When back in the classroom, you will receive the correct molar mass of the acids so you can calculate the percent error.
D- Calculation of Molarity of a soft drink solution
1. Repeat steps 1-4 from Section B to prepare for the titration of the soft drink solution. 2. Take the soft drink solution from a buret on the back lab table recording the initial and final volume from the soft drink buret. Add approximately 40 mL of the soft drink to your flask. Make sure you record the exact volume to the 100ths place. Do not add water to your flask. 3. Each group should have 3 titrations completed. Accept the values that are within 0.01M of each other. Calculate the average of all the acceptable values.
In this lab experiment, overall, I learned how to titrate. The concentration of one solution was determined by its reaction with a standard solution. The molar mass of unknown acids were also calculated. While learning to titrate, I learned several other skills in the process. I learned how to prepare a standard solution of sodium hydroxide, how to standardize a sodium hydroxide solution by using potassium hydrogen phthalate (KHP), how to find the molar masses of unknown organic acids when given whether the acid is monoprotic, diprotic, or triprotic, and how to calculate the molarity of a soft drink. At the same time, other skills were practiced. Skills such as calculating molarity, molar mass and percent error were exercised. The molarity was calculated for part B, the standardization of sodium hydroxide.
After all of the molarities were calculated, five of them were accepted and the average came out to be 0.0935, which was the number that would be used throughout the lab to help calculate the molar masses of the unknown acids and the molarity of a soft drink. The molar mass was calculated for the unknown acids A, B, and C. Molar mass is grams of solute divided by the average molarity multiplied by the total amount of liters. In acid A, five molar masses were accepted and the average came out to be 180.0440. In acid B, only three molar masses were accepted and the average came out to be 154.5841. In acid C, there were four of the the molar masses accepted and the average came out to be 180.6426.
The percent errors of the unknown acids were relatively small with the exception of acid C. For acid A the percent error was 2.22%, for acid B it was 2.99%, and for acid C it was 13.54%. The percent error for acid A and B is small because of how much NaOH was used. The amount was always less than below 40.00 grams except for once, and most of the time the amount of NaOh was in the 20s or below. During the trials for acid C, the amount of NaOH used was no less than 33.90 grams for each trial. In Part D of the experiment, the molarity of a soft drink solution was calculated. Ginger Ale was mixed with NaOH solutions. This titration resulted in a pink, dark peach and a dark, dark peach color. Of three molarities recorded, all three were accepted. The averages of the accepted molarities of Ginger Ale were 0.0311.