PERCENT ACETIC ACID IN VINEGAR EXPERIMENT 15 PURPOSE A will be titrated using a standardized to determine the percent acetic acid by mass. INTRODUCTION In order to determine the concentration of a, there must be something to compare it against (benchmark). This benchmark is referred to as a standard. Sodium hydroide (basic) is typically used as a standard to determine the concentration of acids. When an acid and base react, they form salt and water (neutral). acid base salt water A titration measures the volume of a added to a reaction using a buret. A buret is a long tube that is typically calibrated in milliliters. The acid and base are reacted together until one of the two is completely reacted. That point is called the endpoint that is neutral. If any additional acid or base is added, the will then become acidic or basic depending on which was added in ecess. To visually determine the endpoint, an indicator is added to the reaction. An indicator is a chemical that changes colors at a particular ph. Since an acid base reaction upon completion is neutral, an indicator is used to visually indicate the point at which just a tiny ecess of the acid or base is added beyond the completion of the reaction. In order to use a standardized, the must be prepared. After preparation, the eact concentration of the standard will be known. In this eperiment, a standardized sodium hydroide ( will be used. Using basic stoichiometry, the acetic acid (CH COOH) in the can be determined from the added to the reaction. CHCOOH CHCOONa H2O Note the molar relationship. For every one mole of acetic acid, it would take one mole of to completely react it. For every one mole of, it takes one mole of acetic acid to react with it. acetic acid
In the titration, the is added drop-by-drop using the buret. The buret indicated how much is being added to the. At the point where all the acetic acid in the has been reacted (endpoint) any additional will turn the basic. The indicator, phenolphthalein, in a basic turns the from clear to pink at this point. The volume of added to the is read off the buret in milliliters and converted to liters (liters = ml / 1000) The the sodium hydroide used to react with the acetic acid in the can now be determined. (molarity of (liters of Eample: 25 ml of a is titrated with 40 ml of a standardized 0.1 M. How many were used and how many acetic acid were reacted. Solution: liters of ml of 1000 40 ml of 1000 0.04 liters (molarity of (liters of 0.1 M 0.04 liters 0.004 moles acetic acid Therefore, the acetic acid in the are 0.004 moles. The mass of the acetic acid in the is determined by using the acetic acid and the molecular mass of acetic acid (60 g/mol). grams of CHCOOH (molecular mass of CHCOOH) ( CHCOOH) Eample: Calculate the grams of acetic acid in the if the molecular mass of acetic acid is 60 g/mol and there is 0.004 acetic acid. Solution: grams of grams of CH COOH CH COOH ( molecular 60 g / mol mass of CH COOH) 0.004moles 0.240 grams ( CH COOH)
In order to calculate the percent acetic acid in the by mass, we will assume the density of the is the same as water (1.00 g/ml). grams of density of volume of Eample: Calculate the mass of the, if 5 ml of the was used in the titration (assume the density of the is 1.00 g/ml). Solution: grams of density of volume of grams of 1.00 g / ml 5 ml 5 grams To calculate the % acetic acid by mass in the : % acetic acid in grams of acetic acid grams of 100 Eample: Calculate the % acetic acid by mass in the if the mass of the was determined to be 5 grams and the mass of the acetic acid was found to be 0.26 grams. % acetic acid in grams of acetic acid grams of 100 % acetic acid in 0.26 grams of acetic acid 5 grams of 100 4.72 % acetic acid PROCEDURES PREPARATION OF BURET 1. Clean a 50 ml buret and rinse with DI water. A clean buret will have no droplets clinging to inside of the glass.
2. Rinse the buret with two 5 ml portions of the standardized. Make sure you drain the through the tip of the buret.. Using a funnel, fill the buret with the standardized. Make sure that the tip is also filled and there are no air bubbles in the tip. 4. Slowly drain the out of the buret until the buret reads 0.0 ml. Read from the bottom of the meniscus. It is sometimes helpful to hold a piece of paper with a black line behind the buret and line it up with the meniscus. PREPARATION OF THE VINEGAR SOLUTION 5. Pipet 5 ml of the into a clean 250 ml flask. 6. Add 50 ml of DI water to the flask. 7. Add two drops of phenolphthalein indicator. DETERMINATION OF % ACETIC ACID IN A VINEGAR SOLUTION 8. Place a white background underneath the flask with the. 9. Slowly add with constant swirling the drop wise to the. 10. Continue adding drop wise to the until the turns the faints shade of pink that remains for 0 seconds. This is called your endpoint. 11. Calculate the % by mass of acetic acid in the.
NAME DATE SECTION DETERMINATION OF % ACETIC ACID IN A VINEGAR SOLUTION REPORT SHEET Eperiment 15 Titration of Vinegar Solution Trial 1 Trial 2 Trial Final buret reading in ml Initial buret reading in ml Volume of added (final initial) in ml Volume of added in liters (ml / 1000) Molarity of Standardized Moles of (molarity liters Moles of Acetic Acid Molecular Mass of Acetic Acid (g/mole = amu) 60 g/mole 60 g/mole 60 g/mole Grams of Acetic Acid (moles acetic acid 58 amu) Density of Vinegar Solution 1.00 g/ml 1.00 g/ml 1.00 g/ml Volume of Vinegar Solution Titrated 5 ml 5 ml 5 ml Grams of Vinegar Solution (density of volume of Vinegar Solution) % Acetic Acid in Vinegar Solution Grams of Acetic Acid (moles acetic acid 60 amu) Average % Acetic Acid in Vinegar Solution
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