ChemLab - Chemistry 3/5 - Hot and Cold Reactions

0 ChemLab - Chemistry 3/5 - Hot and Cold Reactions - Procedure

Calorimetry 2: Hot and Cold Reactions

Overview

Getting Started

Techniques

Procedure

FAQ

Full Lab Manual

Introduction & Goals

Chemistry & Background

Key Questions

Prelab Problems

Safety

Procedure

In Your Write-up

Experiments Index

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Techniques
This week, you will use a coffee cup calorimeter to determine heats of reaction in solution, just as you did last week. Review the Techniques section of last week's experiment on the ChemLab website and review your lab notebook to recall key points. Be sure that your calorimeter is dry when you begin each experiment and that the volume of water or solution is measured accurately. Finally, remember that the most accurate way to determine

T is by plotting temperature vs. time and extrapolating.

Procedure
This week, you and your lab partner will work out the details of the procedure on your own. An outline of the measurements you will need to make is given below. The salts available in the lab are listed in the table given on the In Your Write-up page.

Decided on two salts to investigate
With your partner, choose one hot and one cold pack candidate, considering your results for Prelab Problem 2.

Calculate how much salt to use
For each of your chosen compounds, you will need to use an amount that will give a temperature change between 2.5 and 3 K. This calculation should be done before coming to lab, as part of your prelab write-up.

Determine the heat capacity of the calorimeter
Your value from last week is a good starting point. Confirm that value with at least one more measurement this week. HCl and NaOH solutions will be available at the concentrations used last week.

Determine the experimental H for the dissolution of each salt you have chosen
Use your solution calorimeter to measure the temperature change for each dissolving salt. Then calculate the enthalpy change and the molar enthalpy change for your two compounds. Compare to the literature values to see how you are doing. Repeat the determination at least once for each of your compounds. You should do a minimum of four runs.

Analyze your results
With your partner, be sure that you have a complete set of data and that you can address each of the discussion points listed on the In Your Write-up page.