How do you prepare a 25% v/v ethylenediamine solution in the laboratory?

Measure 50 mL of ethylenediamine using a graduated cylinder and transfer it to a 200-mL volumetric flask. Add deionized water until the solution reaches the calibration line on the flask. Add a magnetic stir bar and mix on a stir plate for one to two minutes until homogeneous. This produces 200 mL of the target solution.

What safety precautions are required when working with ethylenediamine?

Ethylenediamine is toxic, caustic, flammable, and corrosive, so all work must occur in a fume hood. Wear a lab coat, chemical splash goggles, and gloves as personal protective equipment. Store the prepared solution in a flammables cabinet until needed to prevent exposure and fire hazards.

What glassware and equipment should be set up at each student workstation?

Each pair of students needs two 10-mL graduated cylinders, beakers of various sizes (100, 400, 600, and 800 mL), a 500-mL filter flask, a Büchner funnel, a glass stirring rod, filter paper, and a rubber policeman. Additional supplies include lab tape, silicone tubing, disposable pipettes, and squeeze bottles of deionized water and acetone.

How should the ethylenediamine solution be stored after preparation?

Transfer the cooled solution to a labeled brown glass dispensing bottle with a 20 mL capacity pump. Store the bottle in a flammables cabinet until use. Proper storage prevents degradation, minimizes exposure hazards, and maintains solution integrity for laboratory experiments.

What waste disposal setup is needed before starting the experiment?

Label separate waste containers for organic, aqueous, and solid nickel waste according to your institution's disposal procedures. Place labeled containers in an approved waste collection area. This organization ensures proper segregation and safe handling of different waste types generated during the experiment.

Why is a volumetric flask used instead of a regular beaker for solution preparation?

A volumetric flask provides precise volume measurement with its calibrated mark, ensuring accurate concentration of the final solution. The narrow neck and flat bottom allow exact filling to the target volume, which is critical for preparing solutions with specific v/v percentages required in stoichiometric calculations.

Stoichiometry, Product Yield, and Limiting Reactants

Concepts Instructor Prep Student Protocol

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In chemical reactions, atoms — which are the building blocks of reactants — are rearranged to form new entities called products. The law of the conservation of masses states that matter can neither be created nor destroyed. Thus, for a chemical reaction in an isolated system, the mass remains constant.

The number of atoms on the reactant side equals that on the product side, and we see that the equation is balanced. This relationship between reactant and product quantities is known as stoichiometry.

Now, let's practice balancing a chemical equation. Here are the coefficients for carbon dioxide and nitrogen dioxide to help you get started. First, let's count the number of atoms on each side. Pay attention to both the coefficient, which indicates how many molecules are in the equation, and the subscript, which tells us how many atoms are in a molecule.

Then, multiply the coefficient and subscript values for each atom. Repeat for all elements. If an element is in several molecules, simply add the number of atoms in each molecule. Once this is complete for all elements, check to see if the reaction is balanced.

At its current state, the equation is not balanced. We see that there is one nitrogen on the reactant side, but four on the product side. To balance nitrogen, we need four reactant molecules, so we multiply all its elements by four. This balances carbon as well. There are two hydrogen atoms on the product side. Thus, we will make 14 H2O products. This makes 38 oxygen atoms on the product side, which requires 19 oxygen molecules on the reactant side. Finally, the equation is balanced.

The relationship between coefficients represents the relationship between the molar amounts. In this equation, one molecule of methane reacts with two molecules of oxygen to make one molecule of carbon dioxide and two molecules of water. The reaction stops when any reactant is completely consumed, limiting the amount of product that can be made. That reactant is called the limiting reactant.

The maximum possible amount of product, which is called the theoretical yield, depends on the amount of the limiting reactant. However, the actual product yield may differ based on side reactions, loss from purification steps, or human error. The percent yield tells us what percentage of the theoretical yield was obtained and is determined with this equation.

In this lab, you will react nickel chloride hexahydrate with ethylenediamine to synthesize a nickel coordination complex. Then, you will measure the amount produced, determine the limiting reactant of the reaction, and calculate the percent yield of the product.

At the end of this lab, students should know...

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.