Question

Below is a lab hand out for the questions. All my data for the questions are filled out below in BOLD LETTERING. All the questions I need answered are at the bottom with boxes where to put the answers.

Background

Alka-Seltzer^� is an over-the-counter antacid and pain relief drug. The tablet contains aspirin (acetylsalicylic acid), citric acid, and sodium bicarbonate (NaHCO₃). Sodium bicarbonate (NaHCO₃) is responsible for the effervescent action of Alka-Seltzer.

In this lab we will investigate the reaction of sodium bicarbonate, a main component of Alka-Seltzer, with acids. This is a type of neutralization reaction because the acid is neutralized by the bicarbonate ion, HCO₃^-. We will start by running the reaction with two different acids: hydrochloric acid (HCl) and vinegar, which is an aqueous solution of acetic acid (CH₃COOH or HC₂H₃O₂). It's kind of like an acid-base exchange reaction, however the H₂CO₃ produced immediately decomposes to CO₂ gas and liquid H₂O.

When dissolving Alka-Seltzer in just water, the NaHCO₃ can react to some extent due to the presence of the citric acid and the aspirin (acetylsalicylic acid), so that's why bubbles form. Additional excess acid, such as HCl or vinegar, will help the sodium bicarbonate react completely.

In the first experiment, you will observe how Alka-Seltzer reacts with hydrochloric acid, HCl(aq), and then with the acid in vinegar, HC₂H₃O₂(aq). You will use your observations and what you've learned from Chapter 4 about predicting products of netralization reactions to write balanced equations for these chemical reactions.

In the second experiment, you will vary the relative amounts of Alka-Seltzer and vinegar. Because CO₂ gas is released from the reaction, you can determine the mass of CO₂ produced in the reaction from the change in mass during the reaction. Once you know the mass of CO₂ produced, you can use stoichiometry to determine the amounts of reactants that reacted. Specifically you will determine the mass of NaHCO₃ reacted for each trial using different combinations of reactants. By plotting a graph of the calculated mass of NaHCO₃reacted against the amount of vinegar in the water-vinegar solution, you can find the amount of NaHCO₃in the Alka-Seltzer sample. The goal is to determine the composition as percent-by-mass as a measure of the strength of the antacid. A secondary goal is to further explore the concept of limiting reactants.

Lastly, reporting data and calculated values with the correct number of signifdicant figures is important. Be sure to use at least 4 significant figures for molar mass values used in calculations. Rounding to fewer significant figures can reduce the accuracy of your calculated values.

Procedure

Experiment 1: Determining the Nature of the Reaction

1. Take two 50 mL beakers from the Containers shelf and place them on the workbench.

2. Add 35.00 mL of 1 M HCl to the first beaker. Be sure to label the beaker with its contents by double-clicking on the beaker.

3. Add 35.00 mL of the 5% vinegar solution to the other beaker. Also label it.

4. Place a balance from the Instruments shelf onto the workbench. Determine the mass of each beaker with the solution.      MASS #1 HCl: 120g                  MASS #2 Vinegar: 120.093

5. To each beaker, add 4.000 g of Alka-Seltzer.

6. Record your visual observations. Did a chemical reaction occur? Yes Bubbling/Fizzing

7. Weigh each beaker again and record the mass in your Lab Notes.     #1= 122.822     #2= 122.916

8. Calculate the change in mass that occurred during the reaction. Be sure to include the 4.000 g of Alka Seltzer in your initial mass prior to reaction.    Change in mass for #1= 1.178                #2= 1.777

9. Based on your qualitative and quantitative observations, and your knowledge of neatralization reactions you learned in Chapter 4, identify the chemical reaction that occurred in both beakers.

? Acid-Base Nuetralization Reaction??? (IM NOT SURE)

Experiment 2: Determining the Percent-By-Mass NaHCO₃ in Alka-Seltzer

1. Move a balance from the Instruments shelf to the workbench.

2. Take nine 50 mL beakers from the Containers shelf and place them on the workbench.

3. Weigh each beaker and record its mass in your lab notes. EACH BEAKER WEIGHS = 85g

4. Add the 5% vinegar solution and distilled water from the Materials shelf to each of the beakers in the amounts specified in the following table:

Beaker	5% Vinegar (mL)	Distilled Water (mL)
1	0.0	35.0
2	2.5	32.5
3	5.0	30.0
4	7.5	27.5
5	10.0	25.0
6	12.5	22.5
7	15.0	20.0
8	17.5	17.5
9	20.0	15.0

Assume each volume was measured using volumetric glassware with precision to one decimal place.

5. Weigh each beaker again and record the mass for each in your labs notes.

BEAKER 1: 120g

BEAKER 2: 120.007 g

BEAKER 3: 120.013

4: 120.020

5: 120.027

6: 120.033

7: 120.040

8: 120.047

9: 120.053

6. Add 4.000 g of Alka-Seltzer to each beaker. Wait until all of the bubbling stops.

7. Weigh each beaker with final solution and record the mass of each in your lab notes.

BEAKER 1: 123.090 g

BEAKER 2: 122.994 g

BEAKER 3: 122.898

4: 122.842

5: 122.849

6: 122.856

7: 122.862

8: 122.869

9: 122.876

Alka Seltzer Strength

Experiment 1: Determining the Nature of the Reaction

1. Based on the Background information, what product of the reaction causes the bubbling to occur when Alka-Seltzer is added to an acid?

CO2

2. Based on the Background information, what component of Alka-Seltzer reacts with the HCl and the vinegar? Write its name and chemical formula.

3. Use the Background information and Chapter 4 in your textbook as a reference to write balanced equations (including physical states) for the reactions you observed:

(a) Write a balanced equation for the reaction of solid sodium bicarbonate with HCl(aq).

(b) Write a balanced equation for the reaction of solid sodium bicarbonate with the acid that�s in vinegar, acetic acid, HC₂H₃O₂(aq).

4. Explain why the other components of Alka-Seltzer should not react with HCl or vinegar to product a gas.

5. Fill in the table below with your recorded data and calculated results for Experiment 1.

BEAKER #	(1) Initial Mass (g)	(2) Final Mass (g)	(3) mass CO2 evolved (g)	(4) moles CO2 evolved (mols)
1
2

6. Identify the limiting reactant in these reactions. Explain how you determined the limiting reactant.

Experiment 2: Determining the Percent-By-Mass NaHCO₃ in Alka-Seltzer

Be sure to report all data and calculated results with the correct number of significant figures.

7. Fill in the table below with your recorded data and calculated results. More descriptive instructions for each column are below the chart. For some of the columns you�ll need to show a sample calculation.

BEAKER #	(1) Initial Mass (g)	(2) Final Mass (g)	(3) mass CO2 evolved (g)	(4) moles CO2 evolved (mols)	(5) moles of NaHCO3 reacted (mols)	(6)mass of NaHCO3 reacted (g)
1
2
3
4
5
6
7
8
9

Column 1: This initial mass (before reaction) is the measured mass of the beaker containing the water and vinegar PLUS the mass of the Alka-Seltzer tablet (4.000 g).

Column 2: This final mass is the measured mass of each beaker with its solution after the reaction between the Alka Seltzer with the vinegar and water.

Column 3: Calculate the mass of CO₂ evolved in each beaker by subtracting the final mass from the initial mass. Show calculation for Beaker 9 here.

Column 4: Calculate the number of moles of CO₂ evolved in each beaker.    Show calculation for Beaker 9 here.

                     

Column 5: Calculate the number of moles of NaHCO₃ that reacted in each beaker. Show calculation (or explain your answer) for Beaker 9 here.

  

Column 6: Calculate the mass of NaHCO₃ that was used up in the reaction for each beaker. Show calculation for Beaker 9 here.

8. Create a graph with nine data points by plotting the mass of reacted NaHCO₃ in each beaker (y-axis) against the volume of vinegar (x-axis).

Insert Graph Here

                                              

                                              

9. Use the graph of your results to answer the following questions:

(a) In which trials (beaker numbers) was NaHCO₃ the limiting reactant?

(b) Which trials (beaker numbers) can you use to calculate the amount of NaHCO₃ that reacted?

(c) Which trials (beaker numbers) can you use to calculate the amount of NaHCO₃ present in the Alka-Seltzer samples?

                

(d) What is the mass of NaHCO₃ in an Alka-Seltzer tablet? Explain how you arrived at your result.

  

(e) What is the percent-by-mass composition of NaHCO₃ in the Alka-Seltzer tablet? Show your calculation here.

(f) Explain why the %NaHCO₃ value you calculated in the previous question is a good measure of antacid strength.

Answer 1

Experiment 2 Acid-base Neutralization reaction HC1 +HCO CH3COOH +HC03--> CH3COO-+ H2O+ CO2 lmol of CH3COOH consumes one mole of HCO3 and produces a mole of CO2 Therefore no.of moles of CO2 should be calculated. Which is equal to no.of moles of NaHCO3 Cl +H20+CO2 Beaker Beaker+ After reaction difference reactants 124 124.007 124.013 124.020 124.027 124.033 124.040 124.047 124.053 122.090 122.099 122.898 122.842 122.849 122.856 122.862 122.869 122.876 0.91 1.013 1.115 1.178 1.178 1.178 1.178

To calculate no.of.moles of CO2 3. From the table the mass difference from beaker 4 to 9 is same Take average 1.178 1.178+1.177 +1.178+1.178+1.177 Mass of CO2 evolved is 1.177g

No. of. Moles of CO2 (nco) Mass c Molar mass 1.17767 -0.02675 moles 5. No of moles of CO2- No of moles of NaHCO3 -0.02675moles 6. Mass of NaHCO3 Molecular weight of NaHCO3Moles of NaHCO - 84x0.0267 - 2.2483g