Use the information in the section of the experiment entitled \"Complete Convers

Question

Use the information in the section of the experiment entitled "Complete Conversion of Acetylsalicylic Acid to Salicylic Acid" to answer the following 2 questions below.

You weigh three samples of crushed aspirin tablet into separate Earlenmeyer flasks, dissolve each in 20 mL of ethanol, and add three drops of phenolphthalein indicator to each. You then use a 50 mL buret to add 0.10 M standardized NaOH to the first sample, which turns pink after the addition of 15.68 mL.

1. What volume (in mL) of additional standardized NaOH should you add to the first sample?

2. What is the total volume (in mL) of NaOH added to the first sample?

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PROCEDURE BELOW:

ll. Complete Conversion of Acetylsalicylic Acid to Salicylic Acid Obtain the combined weight of three aspirin tablets by taring a clean, dry weighing bottle, then adding three aspirin tablets. Be sure to record the brand of aspirin and mass of ASA per tablet according to the manufacturer. 7. 8. Use a dry mortar and pestle to crush the three tablets into a fine powder. Transfer most of the 9. Weighing by difference, add approximately 0.25-0.30 g of the ground aspirin tablets into each 10. To each aspirin sample, add 20 mL of ethanol to dissolve the ASA. Some solids from the powder to a clean, dry weighing bottle (it is not necessary to transfer all of the powder). of three different Erlenmeyer flasks, noting the exact mass for each. coating or fillers will remain; this is normal, and will not affect the results. Add three drops of phenolphthalein indicator. Mix thoroughly. 11. Set up three water baths on a hot plate using 600-mL beakers. Add two or three boiling chips to each beaker. Only one large hot plate per bench should be used at a time (multiple small plates may be used along with a large plate). Additional large hot plates can be set up on the front and back benches, and on the bench by the flame photometers. 12. Titrate the first aspirin sample with NaOH to the first permanent cloudy pink color. This endpoint indicates the ASA has been neutralized to its conjugate base. However, this is not an accurate equivalence point because the conjugate base also reacts with hydroxide ion To ensure that both reactions proceed to completion, add more NaOH until you have added twice the initial endpoint volume, then add an additional 10 mL. There is no need to titrate the other two aspirin samples - simply add the same total amount of NaOH to each. Record the exact (to two decimal places) amount of base added to each aspirin sample. 13. Put each flask in a pre-heated water bath to speed up the hydrolysis reaction. The waterin the flasks occasionally. After 15 minutes, remove the samples from the water beakers may boil, but avoid boiling the solutions, because the sample may decompose. While heating, swirl the baths and cool for 5 minutes. If the solution is colorless, add three more drops of phenolphthalein. If the solution remains colorless, add 10 mL more of the base and reheat the solution. Accurately record the volume of any additional base added.

Explanation / Answer

From the information you have provided, point 12 says:

Add more NaOH until you have added twice the initial endpoint volume, then add an additional 10 ml

So for the first question you will need to add 15.68 ml and 10 ml more, this is equals to 25.68 ml

Second question total volume

initial 15.68

second addition 15.68

excess of 10

Total volume = 15.68 + 15.68 + 10 = 41.36 ml

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