CHM110H5 Lecture Notes - Lecture 1: Molar Mass, Titration, Saponification

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14 Apr 2016

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Aspirin or acetylsalicylic acid is an organic acid with the formula c9h8o4. In this experiment, the purity of commercial aspirin tablets and the aspirin synthesized in experiment 5 was investigated using an acid base titration. In some cases it becomes necessary to add an excess of the titrant and then titrate the excess with another reagent, which is termed as being back-titration. By using the technique of back titration, thus knowing the number of moles of titrant added and measuring the number in excess one can calculate the number of moles of analyte present in the original solution. The reaction of acetylsalicylic acid neutralization with the base is given below: H3cc o -- (c6h6) -- co2h + oh- h3cc o -- (c6h6) -- co2. If there are no acidic impurities one can determine the purity of aspirin by simply titrating with a standardized base solution.

Related Questions

Match each term below with its definition or description.

1 The point in a titration when the added amount of standard reagent is equal to the amount of analyte being titrated. 11) End Point

2 The analyte is titrated with the standard reagent and the volume of standard solution required to complete the reaction is measured. 12) Indicator

3 A reagent that is pure and stable, which can be used directly after weighing. 13) Direct Titration

4 The analyte that is being analyzed in the titration. 14) Back Titration

5 Standard reagent is added in excess to ensure complete reaction with the analyte. The excess reagent is then titrated with a second standard reagent. 15) Indirect Titration

6 A solution, whose concentration is known, often made from a reagent of known purity. 16) Primary Standard

7 The standard reagent of known concentration that is added from a buret to the analyte solution. 17) Standard Solution

8 The analyte does not react directly with the titrant so it is converted to another form which will react with the titrant. 18) Titrand

9 The point in a titration when a change in the analyte solution is observed, indicating equivalency. 19) Equivalence Point

10 It is added to the analyte solution and aids in the observation of the completion of the reaction. 20) Titrant

1. Why is a direct titration of the acetlysalicylic acid in the tablet with sodium hydroxide not performed?

	a. Acetylsalicylic acid is a diprotic acid, so a single end point is not possible
	b. Acetylsalicylic acid is a weak acid and does not react very well with sodium hydroxide.
	c. Acetylsalicylic acid is unstable in the presence of sodium hydroxide and will undergo decomposition releasing toxic benzene - to which we do not want our students exposed.
	d. Acetylsalicylic acid undergoes more than one reaction with sodium hydroxide and will not react fast enough in a normal titration.

2. The HCl solution you are using needs to be standardized with Na₂CO₃. If 23.5 mL of HCl is required to react with 0.1127g Na₂CO₃, then what is the concentration of HCl.

3. According to the bottle that the aspirin tablets came in, they contain 325 mg of acetylsalicylic acid (C₉H₈O₄). Determine the number of moles of acetylsalicylic acid in each tablet.

4. How many mL of 0.100 M NaOH is required to react completely with the 325 mg of acetylsalicylic acid in the tablet?

5. If 50.0 mL of 0.100 M NaOH is added to the tablet, how many mL of the HCl (molarity found in question 1) will be required to react with the excess NaOH

6. In the experiment, phenol red will be used as the indicator. What color will phenol red be in a basic solution?

Red

Yellow

Orange

Clear

7. In the experiment, phenol red will be used as the indicator. What color will phenol red be in an acidic solution?

Red

Yellow

Orange

Clear

CHM110H5 Lecture Notes - Lecture 1: Molar Mass, Titration, Saponification

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