Investigating the Heat Associated with Dissolving Ionic Salts in Water Draft 2002 tjg

http://www.chem.iastate.edu/ChemEdGroup/GREENBOWE/sections/projectfolder/flashfiles/thermochem/heat_soln.html

The computer will simulate a calorimetry experiment involving dissolving various ionic salts in water. The following compounds should be available for testing: ammonium nitrate, sodium nitrate, calcium nitrate, magnesium nitrate, sodium chloride, calcium chloride, ammonium chloride, magnesium chloride. Work in pairs and choose two compounds to test. One of your compounds should cause an increase in temperature of the solution, the other compound should cause a decrease in the temperature of the solution.

Write a specific question that you can answer as a result of performing your calorimetry experiment.

Part IA. Design and carry out an experiment to determine the change in enthalpy, 食 (kJ), for the dissolving process for (write the formula of the compound) ___________________________.

In your experiment, what is the dependent variable? ______________________________

What is the independent variable(s)? __________________________________________.

Write an equation that describes the dissolving process for the salt. Classify this process as endothermic, exothermic, or neither.

List the assumptions and or information that you need to make in order to do the calculations.

In your experiment, identify the system ______________ and the surroundings _________________.

In your experiment, what gains heat? ________________________________

What loses heat? _______________________________________________-

Calculations

The heat of reaction, q_rxn for dissolving ____________ in water is ________________.

The change in enthalpy, 食, for dissolving ____________ in water is ________________.

Part IB. Design and carry out an experiment to determine the change in enthalpy, 食 (kJ), for the dissolving process for (write the formula of the compound) ___________________________.

Write an equation that describes the dissolving process for the salt. Classify this process as endothermic, exothermic, or neither.

In your experiment, identify the system ______________ and the surroundings _________________.

In your experiment, what gains heat? ________________________________

What loses heat? _______________________________________________-

Write an equation that relates the heat absorbed to the heat transferred.

.Calculations

The change in enthalpy, 食, for dissolving ____________ in water is ________________.

Part II. Design and carry out a series of experiments that investigates whether or not the amount of compound dissolved in water has any effect on how much the temperature of the solution will change. In your experiment, identify the dependent and independent variables. Make a graph that illustrates a relationship between your variables.

Share your results with your classmates by placing your results on the board.

Questions. Dissolving Ionic Salts in Water (Computer Exercise)

1. Is dissolving an ionic salt in water a chemical or physical process? Explain.

2. Does doubling the amount of substance that dissolves in water correspond to a doubling of a temperature change in the solution?

3. What is the difference between the heat of reaction, qrxn, and the enthalpy of reaction, 食rxn?

4. Can you make a prediction about which ionic compounds will cause an increase or decrease in the temperature of the solution when they dissolve in water?

5. What causes the changes in temperature that you observed to occur (how does it happen)? Draw a diagram at the molecular level that illustrates what is happening. In each case, identify the system and surrounding.