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The Effect of the pH of a Solution on the Rate of Reaction of Alka-Seltzer

Reem Boushahri

Patrick Sonner

SM 1010

April 17, 2017

Rate of Reaction of Alka-Seltzer Lab

Title: The Effect of the pH of a Solution on the Rate of Reaction of Alka-Seltzer

Hypothesis: The reaction rate of Alka-Seltzer tablet is affected by the acidity of the solution. It increases with the acidity of the solution.

Introduction

Alka-Seltzer tablets are made up of citric acid and sodium bicarbonate. These tablets are normally used for the cure of indigestion, cases of hangover, and sour stomach. Alka-Seltzer normally has its pH being 9.2. It is also soluble in water and reacts vigorously. The reaction of Alka-Seltzer involves the reaction of an acid, which is citric acid, and sodium bicarbonate, which is a base, leading to the formation of water and carbon dioxide gas. The other product is a salt as shown in the equation below:

C6H8O7 (aq) + 3NaHCO3 (aq) 3H2O (l) + 3CO2 (aq) + Na3C6H5O7 (aq)

The reaction of Alka-Seltzer is an effervescent reaction and thus Alka-Seltzer tablet will be used in this experiment in solution of varying pH values in order to determine the rate of reaction at the varying pH values. This will be done by measuring the amount of carbon dioxide produced after every 10 seconds. From the hypothesis, the rate of reaction increases with the increase in the pH value of the solution, thus more effervescence will be seen with the increase in the acidity of the solution.

Materials

• 3 effervescent Antacid and Pain Relief Tablets

• Thermometer (degree Celsius)

• 250 ml beaker

• 100 ml graduated cylinder

• Calibrated Scale (for measuring the mass)

• Stop watch (for timing of the reactions)

• Gloves (For hand protection)

Experimental Materials

• Great value lemon juice

• pH meter

• Water

• Paper towels

Experimental Methods

Part 1: Measuring the pH

1. The pH values of deionised water and lemon juice was tested separately and recorded

2. 20 ml of lemon juice and 40 ml of deionised water were measured and poured into a 250 ml beaker

3. The pH of this mixture was then measured and recorded

Part 2: Determining the rate of reaction of Alka-Seltzer in different pH solutions

1. 40 ml of water was measured and poured into a 250 ml beaker and placed on the scale

2. On Alka-Seltzer tablet was then added into the water in the beaker

3. The stop watch was then started and the mass of the solution was measured and recorded after every 10 seconds for a period of 1 minute (60 seconds)

4. This procedure was then repeated for lemon juice and the data was recorded

5. This procedure was also repeated for a mixture of deionized water and lemon juice and the data was recorded.

Results

Data Table 1: Rate of Reaction of Alka-Seltzer in Deionized Water

Total mass lost = 24 grams

Data Table 2: Rate of reaction of Alka-Seltzer in lemon juice

Total mass lost = 0.455 grams

Data Table 3: Rate of reaction of Alka-Seltzer in a mixture of water and lemon juice

Total mass lost = 0.0.514 grams

Figure 1: Graph of the Average Data for the Control Experiment of the Rate of Reaction of Alka-Seltzer in Different pH Solutions

-Taking the fifth and sixth points on the line graph of the water solution to represent the line of best fir, the gradient is 0.02/10 = 0.002.

-Taking the first and the fourth points of the line graph of lemon juice to represent the line of best fit, the gradient is 0.427/40 = 0.011.

-Taking the second point and the fifth point on the line graph of the mixture of lemon juice and water to represent the line of best fit, the gradient is 0.336/30 = 0.011.

From the above gradients, it can be seen that the reaction rate of Alka-Seltzer in water is 0.002; its reaction rate in lemon juice is 0.0427; and its reaction rate in a mixture of water and lemon juice is 0.0336. This supports the hypothesis of the experiment because as it can be shown by these gradient values, the rate of reaction of Alka-Seltzer is evidently increasing with the decrease in the pH of the solution.

Data Table 4: Rate of Reaction of Alka-Seltzer in Deionized Water

Total mass lost = 24 grams

Data Table 5: The Rate of Reaction of Alka-Seltzer in Lemon Juice for the Experimental Average Data

Data Table 6: The Rate of Reaction of Alka-Seltzer in a Mixture of Lemon Juice and Water for the Experimental Average Data

Figure 2: Graph of the Average Data for the Experimental Average Data for the Rate of Reaction of Alka-Seltzer in Different pH Solutions

-Taking the fifth and sixth points on the line graph of the water solution to represent the line of best fir, the gradient is 0.02/10 = 0.002.

-Taking the third and fourth points on the line graph of lemon juice to represent the line of best fit, the gradient is 0.22/10 = 0.022

-Taking the third and fifth points on the line graph of the mixture of lemon juice and water to represent the line of best fit, the gradient is 0.07/20 = 0.0035

From the above gradients, it can be seen that the reaction rate of Alka-Seltzer in water is 0.002; its reaction rate in lemon juice is 0.022; and its reaction rate in a mixture of water and lemon juice is 0.0035. This supports the hypothesis of the experiment because as it can be shown by these gradient values, the rate of reaction of Alka-Seltzer is evidently increasing with the decrease in the pH of the solution.

Discussion & Conclusions

The results of the experiment support the initial hypothesis. This is because the pH of the solution has been shown to affect the rate of reaction of Alka-Seltzer, with its rate increasing with the decrease in the pH of the solution. According to the experimental data results, the slope of the reaction of Alka-Seltzer in water was 0.002; its reaction rate in lemon juice was 0.022; and its reaction rate in a mixture of water and lemon juice was 0.0035. This supports the initial hypothesis of the experiment. The explanation behind the increase in the rate of reaction of Alka-Seltzer as the pH decreases is that an increase in the pH of a solution means that the concentration of H+ ions is also increasing. Since the reaction of Alka-Seltzer is an example of an acid-base reaction, between H+ ions from citric acid and OH- ions from sodium bicarbonate, a decrease in the pH of the solution will increase the reactant’s concentration (Thompson, 2008). This will lead to a forward reaction that favors formation of more products. And according to the particle collision theory, an increase in the amount of reactants will lead to an increase in the number of collisions involved in the reaction. This increases the reaction’s average rate (Moeller, 1980). There are a few assumptions involved in this experiment. One is that the tablets were not contaminated with any chemicals. Secondly is that timing of the reactions may not have been done correctly so it is assumed that all timings corresponded with the intended 10 seconds. The third assumption is that all the masses readings were made without any errors. The fourth assumption is that the Temperature of the reactions was constant during the experiment.

References

Moeller, T. (1980). Chemistry with inorganic qualitative analysis. New York: Academic Press.

Thompson, R. B. (2008). Illustrated guide to home chemistry experiments: All lab, no lecture. Sebastopol, Calif: O'Reilly Media.