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Its purpose to standardize a solution of sodium hydroxide to use the standardized sodium hydroxide solution to titrate the acetic acid in vinegar to determine its percent by mass in vinegar
Typology: Lab Reports
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FV 9/25/
MATERIALS: Four 250 mL Erlenmeyer flasks, two 50 mL burets, liquid funnel, one 150 mL beaker, one 50 mL beaker, 5.00 mL pipet, weighing dish, approximately 0.1 M NaOH, C 6 H4(COOH)COOK (potassium hydrogen phthalate), phenolphthalein, grease pencil.
PURPOSE: The purpose of this experiment is two-fold: (1) to standardize a solution of sodium hydroxide; (2) to use the standardized sodium hydroxide solution to titrate the acetic acid in vinegar to determine its percent by mass in vinegar.
LEARNING OBJECTIVE: By the end of this experiment, the midshipman should be able to demonstrate the following proficiencies:
DISCUSSION:
Vinegar is a solution of acetic acid in water. Acetic acid, CH 3 COOH, is a weak monoprotic acid with a molar mass of 60.05 g/mole. The percent by mass of acetic acid in vinegar can be determined by titrating a known amount of vinegar with a standardized solution of sodium hydroxide, i.e., a sodium hydroxide solution of accurately known concentration. Acetic acid and sodium hydroxide react as shown below:
CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l) 60.05 g/mole
Sodium hydroxide is a hygroscopic solid which means it absorbs water from the air. A weighed quantity of sodium hydroxide therefore contains an unknown mass of water. Therefore, a solution of known molarity cannot be made by dissolving a known mass of solid sodium hydroxide in water. The concentration of a sodium hydroxide solution must be determined experimentally. This is done by titrating the sodium hydroxide solution against a primary standard. A primary standard is a substance from which a solution of known concentration can be prepared. The primary standard used in this experiment is potassium hydrogen phthalate, C6H4(COOH)COOK, which is referred to by the shorthand notation of "KHP". KHP has several advantages: it does not absorb moisture readily (i.e., is not hygroscopic); it is easily dried; it can be accurately weighed; it can be obtained in very pure form; it has a high molar mass of 204.22 g/mole; and it is very soluble in water. KHP is an acid, which reacts in aqueous solution to neutralize the base, sodium hydroxide, as shown below:
C 6 H4(COOH)COOK (aq) + NaOH (aq) C 6 H4(COONa)COOK (aq) + H2O (l) 204.22 g/mole KHP
Part A. Standardization of the Sodium Hydroxide Solution
Part B. Measurement of Acetic Acid in Vinegar
Clean up:
Experiment 15
Part A. Standardization of the Sodium Hydroxide Solution
(A.1) Calculate the moles of KHP for:
Sample 1:
Sample 2:
Sample 3:
(A.2) Realizing you titrated to the equivalence point, use your calculations from Part A to calculate the moles of NaOH for:
Sample 1:
Sample 2:
Sample 3:
(A.3) Calculate the concentration (M) of the NaOH solution for each sample, and then obtain the average value:
Sample 1:
Sample 2:
Sample 3:
Experiment 15
Part B. Measurement of Acetic Acid in Vinegar
(B.1) Use your average value of the NaOH molarity to calculate the moles of NaOH for:
Sample 1:
Sample 2:
Sample 3:
(B.2) Realizing you titrated to the equivalence point, calculate the moles of acetic acid in the 5.00 mL sample of vinegar:
Sample 1:
Sample 2:
Sample 3:
(B.3) Calculate the mass % of acetic acid in vinegar, and then obtain the average value:
Sample 1:
Sample 2:
Sample 3:
Name ___________________________ Section ___________________________
Date _____________________________
Experiment 15
INCLUDE THE APPROPRIATE SIGNIFICANT FIGURES.
mass of X total mass of solution (containing X)