Assignment directions for a project measuring the effectiveness of antacid

Manager of Chem Projects

CheMystery Labs

380 South Buzz Blvd

Bee Hive, UT 84302

Dear Manager:

A consumer group, Truth in Advertisements, would like to check the claims made by various antacid manufactures.  Which antacid is the most effective in neutralizing excess stomach acid?  What antacid is the most cost effective in neutralizing stomach acid?  The group has given a budget of $80,000 to answer their question.

 Before you begin your work, I will need the following information from you so that I can approve your work.  The planning space for these items is found in your project packet.

Ø       a detailed summary of your hypothesis, experimental

      design table, a plan for the procedures along with all

       necessary data tables

Ø       a description of necessary calculations

Ø       an itemized list of equipment with costs and chemical with

      their costs, include labor costs of $80 / hour and cost for

      laboratory space $10,000/day, and a standard disposal

      fee of $2000 / gram of material. 

After you complete the analysis, prepare a report for the group, Truth in Advertisements.  Remember that this report will be seen by a variety of people, so be certain it projects the image we want to present.  The items that should be included in the report are found in your project packet.

Good luck with the project.  Please keep in close contact me as you proceed with the project.  You will need a data verification signature, by having me observe one of the trials in the experiment.

Sincerely

Your teacher

President and CEO

CheMystery Labs Inc.

             Which brand of antacids(                ) neutralizes the

       most stomach acid and which of the brands tested

       is the most cost effective?

Background

                 The the human digestive system makes use of hydrochloric acid in the breakdown of food.  Gastric fluid (stomach acid) is estimated to have a pH of

                one.  This is equivalent to a concentration of 0.10 M HCl.  Antacids are used to reduce stomach acid when it is in excess.

                 The makeup of antacids varies greatly depending on the manufacturer.  Sodium hydrogen carbonate is used in Alka Seltzer.  Calcium Carbonate is

                 used in Tums, Alka-2, and Di-Gel liquid.  Rolaids contains the substance aluminum sodium dihydroxy carbonate.  Sodium-free Rolaids contains

                 calcium carbonate and magnesium hydroxide.  Milk of Magnesia is mostly magnesium hydroxide.  Each of these substances will react to neutralize

                 excess stomach acid.

                    Antacid preparations are sold over the counter for relieving heartburn or acid indigestion.  These symptoms are caused by excess stomach acid,

                    which, for the purposes of this experiment, we can conveniently think of as being pure hydrochloric acid (HCl).  Antacids contain basic substances

                     that either neutralize the excess acid or act as buffers in the stomach.  The types of bases commonly used in actacids include metallic hydroxides,

                     metallic carbonates, or hydrogen carbonates.

                    The net ionic equation for the neutralization of magnesium hydroxide, Mg(OH)₂, a typical metallic hydroxide used in antacids, is shown in equation 1.
 
 

(Eq. 1)           Mg(OH)₂(s)   +   2 H₃O⁺(aq)    --------->  Mg²⁺(aq)   +   4 H₂O(l)

                    In this reaction, 2 mol of hydronium ions (H₃O⁺) react with 2 mol of hydroxide ions (OH^-).  Thus, 1 mol of  hydroxide ions neutralizes 1 mol

                     of H₃O⁺ ions.

                    When calcium carbonate (CaCO₃), a typical metallic carbonate used in antacids, neutralizes HCl, it involves  a two-step process, as shown in

                      Equations 2 and 3.

(Eq. 2)           CaCO₃(s)   +   2  H₃O⁺(aq)  -------->     Ca²⁺(aq)  +  H₂CO₃(aq)  +  H₂O(l)

(Eq. 3)           H₂CO₃(aq)   <--------->   CO₂(g)   +   H₂O(l)

                    In the reaction in Equation 2, 1 mol of carbonate ions (CO₃^2-) neutralizes 2 mol of H₃O⁺ ions.

                    Example of the buffering action of antacids are developed in Equations 4-6.  Equation 4 shows the reaction
                     of carbonate ions, such as those from metal carbonates, with H₃O⁺ ions.

(Eq. 4)        CO₃^2-(aq)   +   H₃O⁺(aq)   <-------->    HCO₃^-(aq)    +    H₂O(l)

                    Hydrogen carbonates ions (HCO₃^-) can react with either OH^- ions or H₃O⁺ ions, as shown in Equations 5
                    and 6.

(Eq. 5)        HCO₃^-(aq)   +  OH^-(aq)  <-------->   CO₃^2-(aq)  +   H₂O(l)
 

 (Eq. 6)        HCO₃^-(aq)   +   H₃O⁺(aq)  <-------->   CO₂(g)   +   2 H₂O(l)

                    Thus, the combination of HCO₃^- and CO₃^2- ions in antacid tablets serves to neutralize acid and to establish
                     and effective buffer system.

                    One method of evaluating antacid preparations is to determine the number of mL of HCl that will react with
                     known mass of antacid.  To accomplish this, we can use an analytical procdure called back-titration.  In a
                     back-titration, we add more standardized HCl solution to the antacid tablet than the tablet can neutralize.  Then
                    we titrate the unneutralized, or excess, HCl with standardized sodium hydroxide solution (NaOH).

                    In general, we can calculate N, the number of mL of HCl neutralized by a tablet, using Equation 8, where A
                    is the number of mL of HCl initially added to a tablet, and B is the number of mL of NaOH required for the
                    back-titration.

(Eq. 8)  N = A - B

                    To compare different brands of antacids, we calculate the mass effectiveness and cost effectiveness of each
                    preparation.  We determine the mass effectiveness of an antacid, E, which is the number of mL of HCl
                    neutralized per gram of tablet, using Equation 11.  N is the number of mL of HCl neutralized by a tablet, and W
                     is the mass of the tablet in grams.

(Eq. 11)  E = N / W
 
 

or/and

                    We can calculate C, the cost effectiveness of a tablet, which is the number of mL of HCl neutralized per
                   one cent ($0.01), using Equation 12.  N is the average number of mL of HCl neutralized per tablet, and P is the
                    cost of one tablet in cents.
 
 

(Eq. 12)      C = N / P

                    In this experiment, you will dissolve a commercial antacid tablet in excess standardized HCl solution.  Next,
                    you will back-titrate the excess HCl with standardized NaOH solution. In this experiment, you will compare the effectiveness

                   of two common  antacids by titrating a known sample of antacid with 0.100 M hydrochloric acid. 

                   Using your data and calculations, you can report on the relative effectiveness of your antacids.

 
 

           TITRATION PROCEDURES

            1. Mass tablet and record.
            2. Dissolve tablet in 25 mL of water.
            3. Add 30mL of 1 M HCl
            4. Add 10 drops of bromothymol blue indicator

(solution should be bright yellow at this point- an Acid solution)

            5. Record beginning reading of the buret.
            6. Titrate the mixture with 1 M NaOH until the solution just barely turns blue-green.
            7. Record the ending reading of the buret.
            8. Repeat for other trials.
            9. Do calculations.
 

Other Ideas for Antacid Research Projects
 

 
 All the solutions and apparatus required for Antacid studies and analysis will be provided, except that you must provide the antacids to be tested.  Here are some general suggestions for the types of projects that you might consider.