How do you prepare a 0.5 M iron (III) nitrate solution in the lab?

Measure 50.5 g of iron nitrate nonahydrate and place it in a 250-mL Erlenmeyer flask using a powder funnel. Add 175 mL of deionized water and stir until homogeneous. Add another 75 mL of deionized water and continue stirring until the solution appears homogeneous again. Transfer the final solution into a labeled polyethylene bottle and store it capped at the back of the instructor's hood.

What personal protective equipment is required before preparing iron (III) nitrate solution?

Wear a lab coat, chemical splash goggles, and gloves before handling iron (III) nitrate nonahydrate. These items protect against chemical exposure and splashes during the preparation of the 0.5 M solution. Always ensure appropriate safety equipment is in place before beginning any chemical preparation work.

What equipment should be set up at each student workstation?

Each workstation requires a hotplate, support rod with medium 3-prong clamp and thermometer clamp, gas pressure sensor device, 20-mL volumetric pipette, pipette controller, beaker assortment (50-mL, 100-mL, three 400-mL, and one 600-mL), Büchner flask, thermometer, rubber stopper, syringe, and stopcock. A 125-mL wash bottle filled with deionized water should also be available at each station.

Why is the iron (III) nitrate solution stirred during preparation?

Stirring ensures the iron nitrate nonahydrate powder dissolves completely and the solution becomes homogeneous. The mixture is stirred after adding the initial 175 mL of water, and again after adding the final 75 mL of water. Continuous stirring on a stir plate promotes uniform distribution of solute throughout the solvent.

What central materials and equipment should be prepared before the lab begins?

Fill an insulated cooler with crushed or chipped ice and place it centrally. Set up a labeled waste container for aqueous iron solutions in the hood. Place a 1-L bottle of 3 wt% hydrogen peroxide in the central hood. Ensure gas pressure sensor devices are charged and working before distribution. Confirm all vacuum sources have silicone tubing attached.

How should the prepared iron (III) nitrate solution be stored?

Transfer the homogeneous solution into a labeled 250-mL polyethylene bottle and cap it tightly. Store the capped bottle at the back of the instructor's hood until just before the lab begins. This storage method protects the solution from contamination and maintains its stability until use.

What glassware and measuring tools are needed for solution preparation?

Use a top-loading balance to measure 50.5 g of iron nitrate nonahydrate, a graduated cylinder to measure deionized water volumes, a 250-mL Erlenmeyer flask for mixing, and a powder funnel for transferring the solid. A stir bar and stir plate facilitate homogenization. A 250-mL polyethylene bottle stores the final solution.

Temperature Dependence

Concepts Instructor Prep Student Protocol

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The measure of how fast a reaction proceeds is called the reaction rate. The rate of a chemical reaction is defined by the rate law, which describes the relationship between the speed of the reaction and the reactant concentrations. In this equation, k is the rate constant, A and B are the two reactants, and m and n are their respective reaction orders.

The rate constant converts the relationship to the proper units of rate, moles per liter per second. Thus, the rate constant has different units, depending on the overall order of the reaction. However, the rate constant holds more significance than simply unit conversion. The rate constant is related to the minimum amount of energy required for a chemical reaction to occur - called the activation energy.

In a reaction, the reactants are at an initial state of potential energy. As the reaction proceeds, it must overcome a certain potential energy, the activation energy, before reaching its final state. The net energy of the reaction is the difference between the initial and final states. This difference can be negative, meaning that the reaction releases energy, or positive, meaning that it absorbs energy.

If there is not enough energy available to overcome the activation energy, the reaction will not proceed. In some cases, energy can be supplied in the form of heat. This provides additional energy to overcome the barrier to activation, and the reaction can proceed. A catalyst may also be added, which provides an alternative lower activation energy pathway between the reactants and products.

Catalysts are not consumed in the reaction and, therefore, do not affect the net energy of the reaction. The activation energy is determined experimentally, and it is related to the reaction constant k by the Arrhenius equation where A is the pre-exponential or frequency factor, R is the universal gas constant, and T is the absolute temperature at which the reaction occurs.

From this equation, we know that increasing the reaction temperature or decreasing the activation energy increases the rate constant. Going back to the rate law equation, it follows that a higher rate constant results in a higher reaction rate. This makes sense because as temperature increases, molecules move faster and collide more frequently, resulting in an increased fraction of molecules with higher energy than the activation energy.

In this lab, you will learn how to measure the activation energy of a reaction experimentally using the decomposition of hydrogen peroxide as the model reaction.

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

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What is the reaction rate, and what factors affect it?

The reaction rate is a measure of the speed of a chemical reaction, and it is described as the change in concentrations over time. Reaction rate is affected by the concentration of the reactants, the temperature, pressure, and the state of matter of the reactants.

What is a reaction's rate law?

A reaction’s rate law is an experimentally determined relationship between the concentration of the reactants raised to their reaction order times the reaction rate constant, k. The constant k is temperature-dependent.

What is the activation energy of a reaction?

The activation energy of a reaction is the amount of energy required for a chemical reaction to occur. If a chemical reaction does not meet this threshold of energy, it will not take place.

How are the reaction rate constant and activation energy of a reaction related?

The reaction rate constant, k, and activation energy of a chemical reaction are related by the Arrhenius equation. This equation states that the rate constant is dependent on the temperature and activation energy of a chemical reaction.

What is a catalyst?

A catalyst facilitates a chemical reaction by lowering the activation energy required. The catalyst is not consumed by the chemical reaction. Catalysts increase the rate of a reaction but do not affect the yield of the reaction.