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# Stoichiometry, Product Yield, and Limiting Reactants

###### Student Protocol
Lab Manual
Chemistry
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Lab Manual Chemistry
Stoichiometry, Product Yield, and Limiting Reactants

## Learning Objectives

#### How does stoichiometry relate the Law of Conservation of Mass to chemical equations?

The amount and atomic composition of products must equal the amount and atomic composition of the reactants. This is because, according to the Law of Conservation of Mass, matter is neither created nor destroyed. The term stoichiometry refers to the ratio of species participating in a chemical reaction.

#### How does one balance a chemical equation?

To balance a chemical equation, you must compare the number of atoms on one side of the equation with the number of atoms on the other. Then, you add coefficients to each reactant and product until the number of atoms are equal or balanced on both sides.

#### What is a limiting reactant, and how can a balanced equation be used to determine which reactant is limiting?

One of the reactants in a chemical reaction will be consumed before the other reactants. This is the limiting reactant because it limits the amount of product that can be formed. To determine which reactant is the limiting reactant, first, calculate how many moles of each reactant are used. Then, multiply this value by the molar ratio of the reactant to the product from the balanced chemical equation. The reactant that results in the least amount of product is the limiting reactant.

#### What is theoretical yield, and how can a balanced equation be used to calculate it?

The limiting reactant will only produce a certain amount of product–this is the theoretical yield. The theoretical yield is calculated by first multiplying the number of moles of the limiting reactant by the molar ratio of the limiting reactant to the product and then converting this amount to grams.

#### What is percent yield?

The percent yield compares the actual yield of an experiment to the calculated theoretical yield. The percent yield is expressed as a percentage.

#### List of Materials

10
• 100-mL glass beaker
5
• 400-mL glass beaker
5
• 600-mL glass beaker
5
• 800-mL glass beaker
5
5
• Glass stirring rod
5
• 83-mm Büchner funnel
5
5
• Neoprene rubber stopper (size 15)
5
• Rubber policeman
5
• Lab tape
5
• Labeling marker
5
• Silicone vacuum tubing
5
• Nickel chloride hexahydrate, (NiCl2·6H2O; 4.5 – 5.0 g/group)
50 g
• Wash bottle with deionized water
5
• 50-mL tall-form glass beaker
5
• 70-mL watch glass
5
• 100-mL polyethylene bottles with acetone
5
• Ethylenediamine
100 mL
• Acetone
500 mL
• Filter paper (70 mm)
10
• 200-mL brown glass bottle with dispensing pump
1
1
• 250-mL beaker
1
1
• Stir plate
1
• Large stir bar
1
• Magnetic wand
1
• Glass funnel
1
• Weighing boat
20
• Crushed ice with scoop
-1 Dependent on lab size
• Analytical balance (at least 1)
-1 Dependent on lab size
• Lab spatula
-1 Dependent on lab size
• Deionized water
-1 Dependent on lab size
• Laboratory wipes (box)
-1 Dependent on lab size
• Disposable 1-mL plastic pipette
-1 Dependent on lab size

#### Lab Prep

Source: Smaa Koraym at Johns Hopkins University, MD, USA

1. Preparation of 25% v/v Ethylenediamine in Deionized Water

Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.

• To set up for this lab experiment, wear the appropriate personal protective equipment, including a lab coat, chemical splash goggles, and gloves. Note: Ethylenediamine is toxic, caustic, flammable, and corrosive. This solution must be prepared and used in a fume hood.
• Prepare 200 mL of a 25% v/v solution of ethylenediamine in deionized water. Pour about 50 mL into a 250-mL beaker.
• Place a powder funnel in a 50-mL graduated cylinder and measure 50 mL of ethylenediamine.
• Transfer the ethylenediamine to a 200-mL volumetric flask. Add deionized water to the flask until the solution level reaches the line.
• Add a magnetic stir bar to the flask, then place it on a stir plate, and mix the solution for approximately one to two minutes until it is homogeneous. Turn off the stir plate when finished.
• Label a brown glass dispensing bottle ‘25% v/v ethylenediamine’. Remove the dispensing pump and use a funnel to transfer the ethylenediamine solution to the bottle.
• Reconnect the glass dispensing pump with a 20 mL capacity to the bottle.
• Retrieve the stir bar with a magnetic wand and set both on a paper towel to absorb the excess liquid. Store the bottle in a flammables cabinet until it is needed.
• When finished, thoroughly clean the volumetric flask, graduated cylinder, funnel, and stir bar, using your lab standard practices. Store the ethylenediamine in its approved storage location.
2. Preparation of the Laboratory
• Fill out labels for organic, aqueous, and solid nickel waste containers according to the waste disposal procedures of your institution. Place the labeled containers in an approved waste collection area.
• Ensure that the following glassware and equipment are available at each workstation (we suggest that students work in pairs):  2    10-mL graduated cylinders 1    100-mL beaker 1    400-mL beaker 1    600-mL beaker 1    800-mL beaker 1    500-mL filter flask 1    Glass stirring rod 1    Büchner funnel (40-mL/83-mm) 1    Filter adapter (size 4) 1    Neoprene stopper (size 15) 1    Rubber policeman 1    Roll of lab tape with pen/marker Silicone tubing
• Set out packages of circular filter paper and disposable 1-mL plastic pipettes so that each workstation has access to them.
• Place at least 3 L of ice in an insulated cooler with a scoop and set out paper towels as needed.
• Obtain a container of nickel chloride hexahydrate and set it by the analytical balances. Verify that the balances have a sufficient supply of weighing boats, clean spatulas, and laboratory wipes.
• Fill five 100-mL polyethylene bottles with acetone. Place a squeeze bottle of deionized water and a bottle of acetone at each workstation.
• Label five tall-form beakers with ‘25% v/v ethylenediamine’. Bring the labeled beakers and five watch glasses to the hood with the ethylenediamine solution.
• When a student group is ready, use the glass pump to dispense 20 mL of ethylenediamine into a labeled beaker. Cover the beaker and carefully hand it to the students.