Experiment 4 PERCENTAGE of ACETIC ACID in VINEGAR

Experiment 5 CONCENTRATION OF ACIDS AND PERCENTAGE OF ACETIC ACID IN VINEGAR Purpose: To determine the concentration or molarity (moles/ liter) of three acids by neutralization with known amounts of sodium hydroxide (base). To determine the percentage by mass of acetic acid in vinegar. Introduction: Acetic acid is produced by the bacterial oxidation of ethanol. Apple cider is often the source of this ethanol. The process stops when the concentration of acetic acid becomes large enough to prevent the bacteria from continuing the oxidation of ethanol. The resulting solution of acetic acid is called vinegar. In this experiment you will titrate the acetic acid in a known mass of vinegar with sodium hydroxide solution of a known concentration. The sodium hydroxide will neutralize the acetic acid. Phenolphthalein is added to indicate the point at which the acetic acid has been completely neutralized by the sodium hydroxide. A knowledge of the concentration (moles per liter) and the volume (liters) of the sodium hydroxide required to neutralize the acetic acid enables us to calculate the number of moles of sodium hydroxide used. Since acetic acid has one ionizable hydrogen atom per molecule, one mole of sodium hydroxide will neutralize one mole of acetic acid. Hence, the number of moles of acetic acid present in the vinegar can be obtained and used to calculate the mass of acetic acid in the known mass of vinegar. Experiment: Pour enough vinegar in a beaker to cover the bottom. (10 – 15 g ) Record the mass of the vinegar. Add 1 drop of phenolphthalein indicator solution to the flask. Obtain about 100 cm3 of 1.00 M sodium hydroxide. Fill the buret and fasten it to a ring stand with a buret clamp. Let some of the sodium hydroxide solution run rapidly from the buret to expel all air bubbles. Read the initial volume of the liquid at the level of the bottom of the meniscus. The meniscus is the curved surface of the liquid. Place the beaker under the buret. With continuous swirling of the flask to ensure thorough mixing, run in the sodium hydroxide solution from the buret until the color changes. (One drop will give you the change!) Read the final volume of the liquid at the level of the bottom of the meniscus. Repeat the above procedure for the other two acids. V(NaOH)/V(Acid) = M(Acid)/M(NaOH) M(NaOH) = 1.00moles/liter

(1) VINEGAR NaOH + CH3COOH  NaCH3COO + H2O Mass of Vinegar: ______grams (1gram = 0.001 Liters) Volume of Vinegar: ______liters Initial reading of buret: ______Final reading of buret: ______Volume on NaOH used (Liters):______(2) Hydrochloric Acid NaOH + HCl  NaCl + H2O Volume of hydrochloric (HCl) acid:______liters Initial reading of buret: ______Final reading of buret: ______Volume on NaOH used (Liters): ______liters (3) Sulfuric Acid 2NaOH + H2SO4  Na2SO4 + 2H2O Volume of sulfuric (H2SO4) acid:______liters Initial reading of buret: ______Final reading of buret: ______Volume on NaOH used (Liters): ______liters

Lab Report: (To be passed in on a separate sheet.) Purpose: What is this labs purpose? Data Table: Acid Volume Acid Volume NaOH

CH3COOH HCl

(a) Determine the concentration of each of the acids. (Molarity = moles / liter: Compare using the inverse ratio.) (Note: For the concentration of H2SO4 double it. Why?) (b) Determine the percent acid in each solution. (Percent = mass of acid / mass of solution X 100) (Sample calculations will be done in class.)