Lab Investigation 5 - What is the optimum mole ratio for a reaction?

An investigation of Mole Ratios and Limiting Reactants

Guiding Question

What is the optimum mole ratio for the formation of CO2 from the reaction of sodium bicarbonate and acetic acid?


You have already learned how to balance chemical equations in terms of molecules, for example see the following equations.
( 1 )
Mg(s) + O2(g) → MgO
( 2 )
2 Mg(s) + O2(g) → 2 MgO 
This information can also be interpreted in terms of moles (of molecules).
( 3 )
2 moles of Mg reacts with 1 mole of O2 to produce 2 moles of MgO 
Why is this useful? With a balanced equation we can predict the moles of products that a given amount of reactants (in moles) will produce. When moles are used, we are then able to count the number of molecules produced by weighing (in grams). Predicting the amount of product formed or determining the amount of reactants needed for a reaction to occur is called stoichiometry. Most stoichiometry calculations are performed using exact mole ratios of reactants and products. In real life, however, many commercial processes for preparing compounds are carried out using an excess amount of one reactant (and thus a limiting amount of the other). For example, if you mix 2.5 moles of O2 with 1 mole of C3H8, 3 moles of CO2 will not be produced because there is not enough O2 added to 'use up' all of the C3H8. Once the O2 is consumed, no more products can be formed, even though some C3H8 remains. In this situation, because the amount of O2 limits the amount of product that can be formed, it is called the limiting reactant or limiting reagent. Therefore, if two reactants are not mixed in the correct mole ratio, the reaction will not go to completion and you will have less product produced and one or more left over reagents.

The Problem

When bicarbonate is mixed with acid, it breaks down into CO2 and H2O. Your task is to design and carry out an investigation to determine the optimum mole ratio for the formation of CO2 by mixing various amounts of sodium bicarbonate and acetic acid. By comparing the amount of carbon dioxide generated when varying amounts of sodium bicarbonate react with a given amount of acetic acid, you should be able to determine the optimum mole ratio of sodium bicarbonate and acetic acid and be able to identify the limiting reactant in the other reactions.

Materials available for use

  • 1.00 M Acetic Acid (HC2H3O2)
  • Sodium Bicarbonate (NaHCO3)
  • Graduated cylinders (1000 mL & 25 mL)
  • Plastic tray
  • Electronic balance
  • Beaker (400 mL)
  • Side-arm flask w/ tubing
  • Ring Stands/Rings
  • Eye droppers

Safety Precautions

Handle acetic acid with care.
Wear goggles at all times, as pressure is built up in this reaction.

Getting Started

Figure 1

Figure 1: Gas collection set-up

You will need to collect gas by water displacement in order to measure the amount of CO2 produced after the mixing of acetic acid and sodium bicarbonate in different molar ratios. Once you have determined the amount of sodium bicarbonate you will need to use in each reaction, conduct your experiments. Be sure to keep in mind the goals of the investigation. NOTE: It may be helpful to prepare a graph of mL of CO2 vs. moles of NaHCO3. Please print the worksheet for this lab. You will need this sheet to record your data.

PDF file

Interactive Poster Session

Once your group has completed your work, prepare a whiteboard that you can use to share and justify your ideas. See the handout provided for details on this process.


Once you have completed your research, you will need to prepare an investigation report that consists of three sections. Your report should answer these questions in 2 pages or less. This report must be typed and any diagrams, figures, or tables should be embedded into the document. Generally, you need one page for the first two sections and the second page for third section.