By: Steve Bintz

Steve Bintz

The Effectiveness of Antacids on HCl

March 13, 2006

Group 4

Proposal (20 points) ______

Notebook (15 points) ______

Peer/Faculty Evaluation (10 points) ______

Report (55 points) ______

Project Grade (100 points) ______

Abstract (Experimental Summary)

The purpose of this experiment was to determine which of two antacids would be the most effective in neutralizing hydrochloric acid. This was done by titrating a standardized solution of acid mixed with an antacid tablet with a standardized base, sodium hydroxide. When the procedure was finished, the number of unreacted moles of acid left was used to determine which tablet neutralized the most and was therefore the most effective. The effectiveness was measured by calculating the amount of acid neutralized by one gram of the antacid. It was determined that Rolaids was the more effective antacid because it neutralized .2312g more of the acid. There are several areas in which errors could be made, however it is believed that these values are accurate due to multiple trials and the use of averages.

Introduction of Methods and Terms

One very important technique is necessary to make this experiment possible. Titration is performed by using one solution to analyze another. 1 In other words, for this experiment, an acid is titrated with a base in order to find out how much is the most effective. Titrations involve the use of an indicator to determine when an endpoint has been reached. An important term throughout this experiment is neutralization. Neutralization simply means that the pH is being brought closer to 7. It is essentially and acid-base reaction which produces a salt. A demonstration of this is found during titration. When an endpoint is reached, it means that all acid or base has been neutralized and the titrant is becoming an excess in the solution. The use of antacids is to make the environment less acidic by neutralizing whatever acid is present.

Results and Discussion

A display of the results can be found in the tables below. Sample calculations are found at the conclusion of the lab report.

Table 1-Standardization of NaOH – from April

Titration / #1 / #2 / #3
H2C2O4Burette 2nd Reading / 44.00 mL / 23.00 mL / 47.00 mL
H2C2O4 Burette 1st Reading / 18.00 mL / 1.49 mL / 22.90 mL
Volume H2C2O4 Used / 26.00 mL / 21.51 mL / 24.10 mL
NaOH Burette 2nd Reading / 19.50 mL / 31.20 mL / 44.20 mL
NaOH Burette 1st Reading / 5.49 mL / 19.56 mL / 31.25 mL
Volume NaOH Used / 14.01 mL / 11.64 mL / 12.95 mL
Molarity of NaOH / 1.118 M / 1.113 M / 1.121 M

Table 2-Standardization of HCl – from Allison

Titration / #1 / #2 / #3
NaOH Burette 2nd Reading / 19.19 mL / 37.69 mL / 18.92 mL
NaOH Burette 1st Reading / .08 mL / 19.19 mL / .15 mL
Volume of NaOH Used / 18.11 mL / 18.50 mL / 18.77 mL
HCl Burette 2nd Reading / 41.98 mL / 20.35 mL / 40.89 mL
HCl Burette 1st Reading / 21.35 mL / .19 mL / 20.70 mL
Volume HCl Used / 20.63 mL / 20.16 mL / 20.19 mL
Molarity of HCl / .9806 M / 1.025 M / 1.038 M

A primary and secondary standard are necessary to have accurate measurements. A primary standard has the characteristics of being very pure, stable and has a known, exact molarity. 2 It is necessary to obtain accurate measurements throughout the experiment, as well as prepare a secondary standard. A secondary standard is a solution which has been prepared using stoichiometry and the molarity is subsequently determined using the primary standard. It is necessary to determine the molarity using the primary standard because often the components are not available in the necessary precision. Table 1 and Table 2 show the molarities of sodium hydroxide, the primary standard, and hydrochloric acid, the secondary standard.

Table 3-Results of Tums Titration

Tablet Titration / #1 / #2 / #3
Weight of Tablet / 1.293 g / 1.291 g / 1.303 g
HCl Burette 2nd Reading / 22.70 mL / 21.40 mL / 37.00 mL
HCl Burette 1st Reading / .38 mL / .41 mL / 16.18 mL
Volume of HCl Used / 22.32 mL / 20.99 mL / 20.82 mL
Initial Moles of HCl / .02265 moles / .02130 moles / .02113 moles
NaOH Burette 2nd Reading / 13.32 mL / 23.30 mL / 29.65 mL
NaOH Burette 1st Reading / 1.88 mL / 13.22 mL / 19.80 mL
Volume of NaOH Used / 11.44 mL / 10.08 mL / 9.85 mL
Moles of NaOH Used / .01278 moles / .01126 moles / .01100 moles
Unreacted moles of HCl / .00987 moles / .01004 moles / .01013 moles

The Tums tablet would be expected to react with acid as shown in Reaction 1:

CaCO3 + 2HCl à CaCl2 + CO2 + H2O (1)

Table 4-Results of Rolaids Titration – from Kelly

Tablet Titration / #1 / #2 / #3
Weight of Half Tablet / .826 g / .701 g / .778 g
HCl Burette 2nd Reading / 22.63 mL / 21.16 mL / 20.35 mL
HCl Burette 1st Reading / 2.40 mL / 1.04 mL / .20 mL
Volume of HCl Used / 20.23 mL / 20.12 mL / 20.15 mL
Initial Moles of HCl / .02053 moles / .02042 moles / .02045 moles
NaOH Burette 2nd Reading / 12.35 mL / 12.18 mL / 13.08 mL
NaOH Burette 1st Reading / 1.31 mL / .30 mL / 1.97 mL
Volume of NaOH Used / 11.04 mL / 11.89 mL / 11.11 mL
Moles of NaOH Used / .01233 moles / .01328 moles / .01241 moles
Unreacted moles of HCl / .0082 moles / .00714 moles / .00804 moles

One would expect the Rolaids tablet to react with hydrochloric acid as shown in Reaction 2:

Mg(OH)2 + 2HCl à MgCl2 + 2H20 (2)

The results shown in Table 3 and Table 4 suggest the Tums antacid to be the most effective. This can be concluded because it neutralized more moles of acid than did Rolaids. However, there are two areas which must be considered before making a determination. First, the Rolaids titration, as detailed in Table 4, was done with approximately one half of a tablet due to an insufficient supply. Here, it is impossible to obtain exactly one half a tablet and human error becomes a great factor, as shown in the varying tablet weights. Secondly, there must be a standardized measure to show how many grams of the acid have been neutralized without having to consider varying weights. In other words, the weights of the Rolaids and Tums tablets will never be exactly equal, so a quantitative measure must be calculated to compare the effectiveness. These issues are resolved by the calculations summarized in Table 5:

Table 5-Summary of the number of grams of HCl neutralized by 1g antacid tablet

Tums / Rolaids
Trial 1 / .3631g / .5443g
Trial 2 / .3180g / .6908g
Trial 3 / .3079g / .4475g
Average / .3297g / .5609g

Table 5 represents the only way to determine which antacid is more effective.

Here, each tablet is shown in terms of the amount of acid it would neutralize if only using one gram. This clearly shows Rolaids neutralizes the most acid and is therefore more effective than Tums.

Experimental error is very prevalent in this experiment. The main place where error occurs is in the reading of the burettes and the determination of when an endpoint has been reached, but not overshot. These two mistakes alone can cause a large variance in measurements as well as make averages falsely represent the data. A loss of tablet mass was very unlikely due to the care taken and very few other areas for error were possible, except for simple calculation errors.

This experiment concluded, through acid-base neutralization reactions, that Rolaids is a more effective antacid than Tums. Titration was the key procedure used throughout these tests by making standard solutions and determining the number of acid moles neutralized. Therefore, when looking for the most effective relief of heartburn, our group suggests taking Rolaids.

References

1)  Zumdahl, Steven S., Zumdahl, Susan A. Chemistry: Sixth Edition. Houghton Mifflin

Company: Boston. 2003.

2)  Chemistry Department. “Standards” Standard Reference Materials. New Mexico

State University. 6 March 2006 <http://www.chemistry.nmsu.edu/Instrumentation/Standards.html

Sample Calculations

Oxalic Acid Molarity:

9.488g | .07530 mol = .3012 M

126.01g/mol | .2500 L

NaOH Molarity:

.3012 mol | .02600 L = .0078312 moles acid | 2 moles NaOH = .0156 mol = 1.118 M

L | | 1 mole acid .01401 L NaOH

HCL Molarity:

1.117 mol | .01850 L = .0206645 mol NaOH=.0205545 mol HCl = 1.025 M HCl

L | L

Initial Moles HCl:
1.015 mol | .02023 L HCl used = .02053 moles HCl

L |

Moles NaOH Used:

1.117 mol | .01104 L = .01233 moles NaOH

L |

Unreacted Moles HCl:

Initial Moles HCl – Moles NaOH Used

.02053-.01233 = .0082 moles unreacted of HCl

Comparison for 1g of tablet

.01144 mL NaOH | 1.117 mol | mole HCl | 36.46 g HCl = .4659g HCl neutralized

| L | mole NaOH| mole

.4659g = HCl neutralized = .3631g HCl neutralized

1.29g 1g