Apple Juice and Antacids Titrations Introduction Ever wondered if there really was a taste difference between a known brand of a product and the store brand? If you did taste a difference, was it just because you “knew” that the store brand tasted worse? Well, in this laboratory experiment, you will work with two brands of apple juice and figure out which brand is more acidic than the other. During the other half of the experiment, two brands of antacids will be titrated. After the titrations are completed, you will know which antacid tablet in fact neutralized more acid than the other. Therefore, you will be able to go out and buy the better antacid tablet! The titrations we will do today involve acids and bases. You will titrate apple juice (acid) with a standardized solution of sodium hydroxide. You will also perform what is called a “back-titration”. After dissolving the antacid in standardized hydrochloric acid, the solution will be titrated with standardized sodium hydroxide until a color change is noticed. For the antacids, you will find out how much acid each antacid tablet neutralized. In order to do this, you must remember that the moles of NaOH used in a titration will be equal to the moles of HCl neutralized in the same titration. As for the apple juice, you will come up with a rough estimate of the concentration of acid in the apple juice brands. After working on the calculations, you will know the truth about the types of apple juice and the two antacids. Materials -Standardized NaOH -Phenolphthalein -Walgreen’s Apple Juice -Rolaids -Methyl Orange -Erlenmeyer Flasks -Buret -Clamps -Weigh Boats

-Standardized HCl -Mott’s Apple Juice -Tums -Mortar and Pestle -Beakers -Graduated Cylinders -Ring Stand -Stirring Rod -Pipettes

Safety Students are to wear safety goggles AT ALL TIMES while in the lab. Even though they will be of low concentration, acids and bases may irritate the skin, so also wear a laboratory coat at all times. Gloves must also be worn. Working with glassware can be dangerous if care is not taken. Be sure to not break any glassware. DO NOT break any burets as they are very expensive. If any glassware is broken during the experiment, call to your lab instructor so he is notified. Grab a brush and dust pan and carefully sweep up any glass on the floor and dump it into a glass container. Make sure all broken glass is off of the lab table. Immediately clean up any spills. Do not drink any of the liquids used in the experiment, and do not eat any of the solids used. Pour all solutions down the drain with water when finished with the experiment.

Procedure -Set up your buret and ring stand. Make sure to obtain at LEAST 100 mL of standardized 0.10 M HCl and at LEAST 100 mL of standardized 0.10 M NaOH. -You may work on either Part 1 or Part 2 first. After finishing both parts, perform more trials if you have enough time / feel like it. 1. Apple Juice Titration -

Grab two 50 mL beakers and fill them halfway with apple juice: one with Mott’s and one with Walgreen’s. Measure out about 10 mL of Mott’s and pour it into a clean 250 mL Erlenmeyer flask. Add 30-60 mL of water and about 5 drops of phenolphthalein. Fill one buret with your standardized 0.10 M NaOH. Make sure the buret is clean. Once everything is in place and the initial NaOH volume reading on the buret is recorded, begin to titrate the apple juice with the NaOH. Remember to constantly swirl the flask. Since the apple juice is yellow, the titration will be complete when the color changes to peach instead of pink. Record your results when the titration is complete. Repeat this procedure with the Walgreen’s apple juice.

2. Antacids Titration -

Weigh out about 0.500 g of crushed antacid and place it into a clean 250 mL Erlenmeyer flask. Measure out EXACTLY 50.0 mL of standardized 0.10 M HCl. Swirl the flask and use your stirring rod to dissolve all of the antacid. Add about 5 drops of methyl orange using a pipette and note the color change. Fill your buret with standardized NaOH and record the initial buret volume reading. Begin to titrate the antacid sample. The titration will be complete when the color changes from pink-red to a pale orange. Be very observant and have a steady hand ready. Repeat this procedure using the other antacid tablet.

Data Collection -

For the apple juice titration, the amount of moles of base used to titrate the sample will equal the number of moles of acid in the sample.

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To find out how much acid was neutralized by the antacids, first figure out how much base it took to neutralize the remaining acid. After finding out how many moles of acid were added to the antacid, the difference of the two numbers should be the amount of moles neutralized by the antacid. Don’t forget the mass of your tablet.

Prelab Questions 1. Predict which apple juice brand you think will be more acidic. Also, predict which antacid tablet will neutralize more acid per gram. 2. Through experimentation, I found my standardized NaOH to have a concentration of 0.9787 mol/L. It took 20.41 mL of this NaOH to completely neutralize 19.56 mL of my standardized HCl. What is the concentration of my standardized HCl? 3. Using the values from #2 above, I decided to titrate a crushed Tums antacid tablet. I mixed 50.0 mL of HCl with 0.5192 g of Tums. After fully titrating the sample, I saw from the buret reading that I had used 9.8 mL of NaOH. Using this information, how many moles of acid did the Tums neutralize? Analysis / Post-Lab Questions 1. Fill out the data table for the experiment. 2. Which brand of apple juice ended up being more acidic? Prove using calculations. 3. Which antacid tablet ended up neutralizing more acid per gram? Prove using calculations. 4. Using your results, which of the two following antacid bottles would you buy? Why? a. Tums: 120 tablets, each tablet is 0.50 grams, for $5.99 b. Rolaids: 100 tablets, each tablet is 0.55 grams, for $5.59

Data Table Concentration of standardized NaOH Concentration of standardized HCl Volume of Mott’s Volume of NaOH used to titrate Mott’s Volume of Walgreen’s Volume of NaOH used to titrate Walgreen’s Mass of Tums Volume of HCl Volume of NaOH used to titrate Tums Mass of Rolaids Volume of HCl Volume of NaOH used to titrate Rolaids