Materials Included In Kit

Additional Materials Required

Prelab Preparation

Sodium Bicarbonate and Acetic Acid Flasks

1. Label three Erlenmeyer flasks 1–3. Using a graduated cylinder, add 10 mL of 2.0 M acetic acid to each flask.
2. Obtain three weighing dishes, and label them 1–3.
3. Measure the appropriate amount of sodium bicarbonate into each weighing dish, according to Table 1.

4. Obtain three balloons. Stretch the balloons.
5. Use a powder funnel to add sodium bicarbonate sample 1 to one of the balloons. Gently tap the balloon so the powder goes to the bottom.
6. Carefully stretch the neck of the balloon over the mouth of Erlenmeyer flask 1. Do not allow the solid to drop into the flask at this time. Repeat steps 5 and 6 with the sodium bicarbonate samples 2–3.

Assigning Hydrogen Volume and Magnesium Mass

7. Assign each group a volume from Part 1 and a mass from Part 2.

Safety Precautions

Hydrochloric acid is a corrosive liquid. Acetic acid is a skin and eye irritant. Avoid contact with eyes and skin and clean up all spills immediately. Magnesium metal is a flammable solid. Keep away from flames and other sources of ignition. Avoid contact of all chemicals with eyes and skin and wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron or laboratory coat. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Some of the leftover solutions may be slightly acidic. These should be neutralized with base (sodium bicarbonate is a good choice) and flushed down the drain with excess water, according to Flinn Disposal Methods #24a and #24b.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. This laboratory activity can reasonably be completed in two 50-minute class periods. The prelaboratory assignment may be completed before coming to lab, and the data compilation and calculations may be completed the day after the lab.
• Instead of having students react the fourth setup for Part A, the teacher can demo the reaction after all students have finished their calculations.
• If you do not have a flexible metric measuring tape, students can use yarn and a meter stick to measure their balloons.
• Remind students that the gas in the filled balloon is not pure hydrogen or carbon dioxide. There will be some air as well.
• Remind students to flatten out the balloon after putting the sodium bicarbonate or magnesium in the balloon. This will help remove excess air.

Answers to Prelab Questions

1. For the first part of lab, you will be using baking soda (sodium bicarbonate) and vinegar (acetic acid). Write the formulas for these two chemicals.

2. Write the balanced chemical reaction between sodium bicarbonate and acetic acid.

NaHCO₃(s) + HC₂H₃O₂(aq) → NaC₂H₃O₂(aq) + H₂O(l) + CO₂(g)

3. If given 5.0 grams of each reactant, how many mL of gas could be collected at a temperature of 25 °C and 1 atm?

5.0 g NaHCO₃ x (1 mol NaHCO₃/84.01 g NaHCO₃) x (1 mol CO₂/1 mol NaHCO₃) = 0.060 mol CO₂
5.0 g HC₂H₃O₂ x (1 mol HC₂H₃O₂/60.06 g HC₂H₃O₂) x (1 mol CO₂/1 mol HC₂H₃O₂) = 0.083 mol CO₂
PV = nRT
(1.0 atm)V = (0.060 mol)(0.08206 L•atm•mol⁻¹•K⁻¹)(273 + 25 K)
V = 1.5 L = 1500 mL

4. If the gas is collected in a balloon, what would you estimate the circumference of the balloon to be when the reaction reaches completion?

V = 4/3πr³
1500 mL = 1500 cm³ = 4/3πr³
1125 cm³ = πr³
(358.1 cm³)^⅓ = (r³)^⅓
r = 7.10 cm
c = 2πr
c = 2π(7.10 cm) = 45 cm

5. For the second part of lab, you will be reacting solid magnesium ribbon with aqueous hydrochloric acid. Write the balanced chemical reaction.

Mg(s) + 2HCl(aq) → H₂(g) + MgCl₂(aq)

Sample Data

Part A. Sodium Bicarbonate and Acetic Acid

Observations:
The balloons increase in size from sample 1 to sample 3. When the reactions are complete, sample 3 has the largest balloon and also has some powder residue left in the liquid at the bottom of the flask. With samples 1 and 2, the liquid at the bottom of the flask is clear.

1. Sodium bicarbonate needed to neutralize 10.0 mL of 2.0M acetic acid (show work): ___1.68 g___

NaHCO₃(s) + HC₂H₃O₂(aq) → NaC₂H₃O₂(aq) + H₂O(l) + CO₂(g)
(0.01 L) x (2.0 M) = 0.020 mol acetic acid
(0.020 mol HC₂H₃O₂) x (1 mol NaHCO₃/1 mol HC₂H₃O₂) x (84.01 g NaHCO₃/1 mol NaHCO₃) = 1.68 g NaHCO₃

__________
Teacher Check

Observations of Fourth Flask:
The sodium bicarbonate and vinegar bubble vigorously as the balloon inflates. When the reaction is complete, the balloon is approximately the same size as the balloon in sample 3. The solution at the bottom of the flask in sample 4 is clear when the reaction is complete.

2. Theoretical volume of the balloon (show work): ___490___ mL

(0.02 mol HC₂H₃O₂) x (1 mol CO₂/1 mol HC₂H₃O₂) = 0.02 mol CO₂
PV = nRT
(0.9980 atm)V = (0.020 mol)( 0.08206 L•atm•mol⁻¹•K⁻¹)(24.5 + 273K)
V = 0.490 L = 490 mL

Theoretical circumference of the balloon:
490 mL = 490 cm³ = 4/3πr³
r = 4.9 cm
c = 2πr = 2π(4.9 cm) = 30.7 cm

Measured circumference of the balloon: ___28.5 cm___

3. Experimental volume of the balloon (show work): ___391___ mL

c = 2πr
28.5 cm = 2πr
r = 4.54 cm 
V = 4/3πr³ = 4/3π(4.54)3 = 391 mL

4. Compare your experimental volume to the theoretical.

The experimental volume is less than the theoretical volume. The balloon is slightly oval shaped and is not a perfect sphere. The percent error for the volume of the balloon is:
% error = [|490 – 391|/490] x 100 = 20.2%

Part B. Magnesium and Hydrochloric Acid, Part 1

Assigned volume of hydrogen gas ___200___ mL

5. Mass of magnesium needed (show work): ___0.20 g___

With a room temperature of 24 °C and a room pressure of 1 atm:
(1 atm)(0.200L) = n(0.08206 L•atm•mol⁻¹•K⁻¹)(24 + 273K)
n =0.0082 mol of hydrogen gas
(0.0082 mol H₂) x (1 mol Mg/1 mol H₂) x (24.31 g Mg/1 mol Mg) = 0.20 g Mg

___________
Teacher Check

Observations:
The magnesium metal is silver colored and easy to break. Once the magnesium is placed into the acid, it bubbles vigorously, inflating the balloon.

Circumference of balloon: ___20.5 cm___

6. Experimental volume of the balloon (show work): ___145 mL___

c = 2πr
20.5 cm = 2πr
r = 3.26 cm
V = 4/3πr³ = 4/3π(3.26)³ = 145 mL
The balloon was also slightly oval.

7. Was any reactant left over? If yes, which one and how much of it was left over?

25.0 mL of 2.0 M HCl
Moles of HCl = (0.025 L)* (2.0 M) = 0.05 mol HCl
(0.20 g Mg) x (1mol Mg/24.31 g Mg) x (2 mol HCl/1mol Mg) = 0.016 mol HCl needed
0.05 mol HCl – 0.016 mol HCl = 0.034 mol HCl leftover
Hydrochloric acid is the excess reactant. If only 0.016 mol HCl is reacted, 0.034 mol of HCl are left over when the reaction is complete.

Part B. Magnesium and Hydrochloric Acid, Part 2

Assigned mass of magnesium solid ___0.45___ g

8. Volume of 2.0 M hydrochloric acid needed (show work): ___18.5 mL___

(0.45 g Mg) x (1mol Mg/24.31 g Mg) x (2 mol HCl/1mol Mg) = 0.037 mol HCl needed
Molarity = moles/Volume
2.0 = 0.037 mol/V
V = 0.0185 L = 18.5 mL

___________
Teacher Check

Observations:
The magnesium metal is silver colored and easy to break. Once the magnesium is placed into the acid, it bubbles vigorously, inflating the balloon. All of the magnesium reacts, no metal is left in the solution.

Circumference of balloon: ___28.5 cm___

9. Experimental volume of the balloon (show work): ___391 mL___

c = 2πr
28.5 cm = 2πr
r = 4.54 cm
V = 4/3πr³ = 4/3π(4.54)³ = 391 mL
The balloon was also slightly oval.

10. Theoretical volume of the balloon (show work): ___450 mL___

With a room temperature of 24 °C and a room pressure of 1 atm:
(0.45 g Mg) x (1mol Mg/24.31 g Mg) x (1 mol H₂/1mol Mg) = 0.0185 mol H₂
(1 atm)V = (0.0185 mol)( 0.08206 L•atm•mol⁻¹•K⁻¹)(24 + 273K)
V = 0.451 L = 450 mL

Introduction

Watch the introduction video.

Concepts

• Stoichiometry

• Law of conservation of mass
• Limiting and excess reactants
• Chemical reactions
• Gas laws

Background

Stoichiometry is used in chemistry to relate moles, mass, volume and more. Depending on the problem, you may have to use units, such as, moles, molar mass or molarity. A balanced chemical equation gives you a plethora of information (see Figure 1).

In addition to giving molar ratios by displaying the coefficients, information about the states of reactants and products is also displayed. For example, in Figure 1 hydrochloric acid is an aqueous solution and carbon dioxide is a gas. One of the most important lessons of stoichiometry is that the amount of the reactants and products in a chemical reaction are related to one another by a mole ratio. The coefficients in a balanced chemical equation summarize the relative number of moles of each reactant and product involved in the reaction. The ratios of these coefficients represent the mole ratios that account for the disappearance of reactants and appearance of products. When a chemical equation is balanced, the law of conservation of mass is obeyed. The mass of the reactants equals the mass of the products.

In addition to calculating moles for stoichiometry problems, you may be asked to perform calculations with volumes. Sometimes this refers to a solution and its molarity. Sometimes you may need to calculate the volume of a gaseous product.

In the case of a gaseous product, if the moles of the gas are known (as well as the pressure and temperature of the system), you can use the ideal gas law to predict the volume of the gas that will be collected. See Equation 1.
where

P = pressure (atm)
V = volume (L)
n = number of moles
R = universal gas constant, 0.08206 L•atm•mol⁻¹•K⁻¹
T = Temperature (K)

Temperature and pressure in the lab will be measured with a thermometer and barometer.

In this lab, in addition to analyzing limiting and excess reactants, you will be collecting various gases in balloons. While the balloons may not inflate to completely spherical, you can measure the approximate circumference of the balloon and calculate the gas collected. With the circumference that will be measured in lab and Equations 2 and 3, you can calculate the volume of gas collected.

c = circumference
r = radius

V = volume
r = radius

Experiment Overview

In this lab, you will be analyzing the stoichiometric relationship of two chemical reactions. In addition to practicing limiting and excess calculations and experiments, you will also be analyzing the volume of gas produced as products.

Materials

Prelab Questions

1. For the first part of lab, you will be using baking soda (sodium bicarbonate) and vinegar (acetic acid). Write the formulas for these two chemicals.

2. Write the balanced chemical reaction between sodium bicarbonate and acetic acid.
3. If given 5.0 grams of each reactant, how many mL of gas could be collected at a temperature of 25 °C and 1 atm?
4. If the gas is collected in a balloon, what would you estimate the circumference of the balloon to be when the reaction reaches completion?
5. For the second part of lab, you will be reacting solid magnesium ribbon with aqueous hydrochloric acid. Write the balanced chemical reaction.
6. (Optional) Explore with the interactive online activity.

Safety Precautions

Hydrochloric acid is a corrosive liquid. Acetic acid is a skin and eye irritant. Avoid contact with eyes and skin and clean up all spills immediately. Magnesium metal is a flammable solid. Keep away from flames and other sources of ignition. Avoid contact of all chemicals with eyes and skin and wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron or laboratory coat. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Procedure

Part A. Sodium Bicarbonate and Acetic Acid

1. Your instructor will have three Erlenmeyer flasks in the front of the room. Each balloon is filled with different amounts of baking soda (sodium bicarbonate). Each flask is filled with 10.0 mL of 2.0 M acetic acid. The balloons are filled as follows:

2. While wearing proper lab attire, look closely at the balloons and solutions that are left when the reactions come to completion. Record your observations on the worksheet.
3. Record the temperature and pressure of the room.
4. To create a sample in which neither reactants are in excess, calculate the mass of sodium bicarbonate needed to completely neutralize 10.0 mL of 2.0 M acetic acid and calculate the volume of gas that will be produced. Show all work on the worksheet.
5. Have your calculations approved by your instructor.
6. Obtain a weighing dish, Erlenmeyer flask and balloon.
7. Pour 10.0 mL of 2.0 M acetic acid into the flask.
8. Weigh out your calculated mass of sodium bicarbonate using the weighing dish and balance.
9. Gently stretch the balloon.
10. Using a powder funnel, transfer the sodium bicarbonate into the balloon. Gently tap the balloon so the powder goes to the bottom.
11. Carefully stretch the neck of the balloon over the mouth of the flask.
12. When ready, lift the balloon and gently shake it to allow the solid to fall into the solution. Make sure the neck of the balloon stays firmly attached to the flask.
13. Record your observations on the worksheet.
14. Do not remove the balloon from the flask! When the reaction is complete, measure the circumference of your balloon with the measuring tape, and record it on your worksheet.

Part B. Magnesium and Hydrochloric Acid

In Part B, you will perform two reactions. Both reactions will react magnesium and hydrochloric acid. Your instructor will assign the target values for your group.

15. Part 1. With 25.0 mL of 2.0 M hydrochloric acid, produce a reaction that creates ______ mL of hydrogen gas.

1. Before performing the reaction, have your instructor sign off on your calculations.
2. Obtain a weighing dish, Erlenmeyer flask and balloon.
3. Pour 25.0 mL of 2.0 M hydrochloric acid into the flask.
4. Weigh out your calculated mass of magnesium metal using the weighing dish and balance.
5. Gently stretch the balloon.
6. Break the magnesium metal into small pieces (approx. 1 cm lengths). Then transfer the magnesium metal into the balloon. Gently tap the balloon so the magnesium is not in the neck of the balloon.
7. Carefully stretch the neck of the balloon over the mouth of the flask.
8. When ready, lift the balloon and gently shake it to allow the solid to fall into the solution. Make sure the neck of the balloon stays firmly attached to the flask.
9. Record your observations on the worksheet.
10. Do not remove the balloon from the flask! When the reaction is complete, have the circumference of your balloon checked by your instructor

16. Part 2. Given ______ g of magnesium, calculate the volume, in mL, of the 2.0 M hydrochloric acid needed to completely react without any excess.

1. Before performing the reaction, have your instructor sign off on your calculations./span>
2. Obtain a weighing dish, Erlenmeyer flask and balloon./span>
3. Pour your calculated amount of 2.0 M hydrochloric acid into the flask./span>
4. Weigh out your mass of magnesium metal using the weighing dish and balance./span>
5. Gently stretch the balloon./span>
6. Break the magnesium metal into small pieces (approx. 1 cm lengths). Then transfer the magnesium metal into the balloon. Gently tap the balloon so the magnesium is not in the neck of the balloon./span>
7. Carefully stretch the neck of the balloon over the mouth of the flask./span>
8. When ready, lift the balloon and gently shake it to allow the solid to fall into the solution. Make sure the neck of the balloon stays firmly attached to the flask./span>
9. Record your observations on the worksheet./span>
10. Do not remove the balloon from the flask! When the reaction is complete, have the circumference of your balloon checked by your instructor.

17. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

14163_Student1.pdf