Lab 6: Alka Seltzer Strength
Fall 2022
Be sure to report all data and calculated results with the correct number of significant figures. Record all
digits when making measurements. Follow the rules for significant figures, and remember that the rules
for addition and subtraction differ from the rules from multiplication and division.
Part 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 the vinegar?
CO2
2. Based on the Background information, what component of Alka-Seltzer reacts with the acid in the
vinegar? Write its name and chemical formula.
Sodium bicarbonate
NaHCO3
3. Use the Background information and Chapter 4 in your textbook as a reference to write a balanced
equation (including physical states) for the reaction you observed when you added sodium bicarbonate to
the acid in vinegar, acetic acid, HC ).
2H3O2(aq
NaHCO3(aq) + CH3COOH(aq) CH3COONa(aq) + H2CO3(aq)→
4. Explain why the other components of Alka-Seltzer (described in the Background) should not react with
acetic acid in vinegar to product a gas.
The other ingredients in Alka-Seltzer are considered neutralizing and the reaction can only occur between an acid
and a base. The neutralizing ingredients cannot aid in producing gas.
5. Fill in the table below with your recorded data and calculated results for Part 1.
BEAKER (1) Initial (2) Final
Mass (g)
(3) Mass
CO2
evolved (g)
(4) Moles
CO2 evolve
d (mols)
#Mass of
beaker &
solution (g)
Mass of Alka-
Seltzer (g)
Mass (g)
1 67.089g 2.000g 69.089g 68.500g 0.589g 0.013mols
Column 1: This (before reaction) is the measured mass of the beaker containing theinitial mass
vinegar solution PLUS the mass of the Alka-Seltzer tablet (2.000 g).
Column 2: This final mass is the measured mass of the beaker with its solution after the reaction
between the Alka-Seltzer with the vinegar.
Column 3: Calculate the mass of CO evolved in each beaker by subtracting the final mass from
2
the initial mass. Show calculation for Beaker #1 here.
69.089g - 68.500g = 0.589g CO2
Column 4: Convert the mass of CO evolved (column 3) to moles of CO evolved. When
2 2
determining molar mass of CO , be sure to use at least four significant figures in your molar mass
2
values obtained from the periodic table. For Beaker #1, write the value for mass of CO
2
evolved and show your calculation here.
0.589g/44.0098g = 0.013mols
6. Which of the following statements is true? Circle or highlight your choice.
A. The mass of the CO gas evolved should be equal to the mass of the Alka-Seltzer tablet.
2
B. The moles of the CO gas evolved should be less than the moles of the NaHCO (in the Alka-
2 3
Seltzer tablet) that reacted.
C. The moles of the CO gas evolved should be equal to the moles of the NaHCO (in the Alka-
2 3
Seltzer tablet) that reacted.
D. The mass of the CO gas evolved should be equal to the mass of the NaHCO in the Alka-Seltzer
2 3
tablet.
Part 2: Determining the Percent-By-Mass NaHCO in Alka-Seltzer
3
Be sure to report all data and calculated results with the correct number of significant figures. Record all
digits when making measurements. Follow the rules for significant figures, and remember that the rules
for addition and subtraction differ from the rules from multiplication and division.
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
CO evolved2
(g)
(4) moles
CO2
evolved
(mols)
(5) moles of
NaHCO3
reacted
(mols)
(6) mass of
NaHCO3
reacted (g)
1 65.000g 64.239g 0.761g 0.01729mols 0.01729mols 1.453g
2 65.005g 64.171g 0.834g 0.01895mols 0.01895mols 1.588g
3 65.010g 64.127g 0.883g 0.02006mols 0.02006mols 1.685g
4 65.015g 64.132g 0.883g 0.02006mols 0.02006mols 1.685g
5 65.020g 64.137g 0.883g 0.02006mols 0.02006mols 1.685g
6 65.026g 64.142g 0.884g 0.02009mols 0.02009mols 1.687g
7 65.031g 64.147g 0.884g 0.02009mols 0.02009mols 1.687g
Column 1: This (before reaction) is the measured mass of the beaker containing theinitial mass
water and vinegar PLUS the mass of the Alka-Seltzer tablet (3.000 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 CO evolved in each beaker by subtracting the final mass from
2
the initial mass. Show calculation for Beaker #7 here.
65.031g – 64.147g = 0.884g CO2
Column 4: Calculate the number of moles of CO evolved in each beaker. (Remember to use
2
molar mass with at least four significant figures in your calculation.) Write the value and show
calculation for Beaker #7 here.
0.884g/44.0098g = 0.0200864353 = 0.201mols
Column 5: Calculate the number of moles of NaHCO that reacted in each beaker.
3Write the
value and show calculation (or explain your answer) for Beaker #7 here.
1mol of CO2/1mol of NaHCO3 = 0.0200864353mols of CO2 → 0.0200864353mols of NaHCO3 =
0.0201mols
Column 6: Calculate the mass of NaHCO that was used up in the reaction for each beaker.
3
(Remember to use with at least four significant figures in your calculation.) molar mass Write the
value and show calculation for Beaker #7 here.
0.884g of CO2/44.0098g/mol = 0.0200864353mols of CO2→ 1mol of CO2/1mol of NaHCO3 =
0.0200864353mols of NaH
8. Create a graph with seven data points by plotting the mass of reacted NaHCO in each beaker (y-axis)
3
against the volume of vinegar (x-axis). Include distinct data points on the graph.
0 2 4 6 8 10 12
1.3
1.35
1.4
1.45
1.5
1.55
1.6
1.65
1.7
1.75
1.45
1.59
1.69 1.69 1.69 1.69 1.69
Reaction of NaHCO3 vs. Vinegar
Reaction of NaHCO3 vs. Vinegar
Volume of Vinegar (mL)
Mass of NaHCO3(g)
Continued….
9. Use the graph of your results to answer the following questions:
(a) Which trials (beaker numbers) can you use to calculate the amount of NaHCO that ?
3reacted
1 and 2
(b) In which trials (beaker numbers) was NaHCO the ?
3limiting reactant
3,4,5,6, and 7
(c) Which trials (beaker numbers) can you use to calculate the amount of NaHCO present in the Alka-
3
Seltzer samples?
3,4,5,6,and 7
(d) What is the mass of NaHCO in each of the Alka-Seltzer “tablets” used in this lab? Explain how you
3
arrived at your result.
Mass of NaHCO3 = avg mass of CO2
Add beakers 3-7 then divide by 5 = 4.417/5 = 0.8834g of CO2/44.0098g/mol = 0.020072802 mols of CO2.
1mol of CO2/ 1mol of NaHCO3 = 0.020072802mols of NaHCO3*84.00684g/mol
Mass of NaHCO3 = 1.6862g
(e) What is the in the Alka-Seltzer tablet? percent-by-mass composition of NaHCO3 Show your
calculation here.
%Mass of NaHCO3 = (mass of NaHCO3 / Mass of tablet) * 100
(1.6862g/3.000g)*100
= 56.208%
Continued…
10. As noted in the background to the lab, each Alka-Seltzer tablet contains acids such as aspirin (acetyl
salicylic acid) and citric acid. These are the only acids that react with the NaHCO in the tablet in
3Trial 1
of Part 2 when no vinegar was added.
(a) How many moles of NaHCO reacted in Trial 1?
3
0.01729mols
(b) How many moles of H (from aspirin and citric acid) with NaHCO in Trial 1. The net ionic
+reacted 3
equation is: NaHCO )
3(s) + H+(aq Na+(aq) + H ) + CO
2O(l 2( )g
0.331mols
(c) Assume that the number of moles of NaHCO that reacted in Trial 1 were not available to react with
3
the vinegar added in later trials. In Table 7 (Column 5), you determined moles of NaHCO that reacted
3
in each trial, which is the moles of NaHCO that reacted in each tablet. Specifically for Trial 7,
3
determine the number of moles of NaHCO in the tablet that are in each tablet to neutralize
3available
stomach acid (HCl) when taken as an antacid. (Show work with units.)
0.02009mols (Trial 7) - 0.01729mols (Trial 1) = 0.0028mols available
(d) Convert moles of NaHCO per tablet you calculated in10(c) to units of /tablet. available 3grams
(Show work)
0.0028mols * 84.00684g/mol = 0.2352g/tablet
11. Use your answer to 10(d) to calculate the to neutralize percent-by-mass composition of NaHCO3 available
stomach acid in each tablet.
%mass = ((0.2352g/tablet)/3.000g)*100 = 7.84%
