Heat of solution lab report answers

Design a Hot Pack or a Cold Pack [footnoteRef:1] [1: Adapted from ChemCollective.org: http://chemcollective.org/activities/autograded/117 by Allan Wilcox, PhD. This lab requires use of a computer with internet access.]

Objectives
· Explain how calorimetry is used to measure heat transfer from a chemical process.

· Measure the heat absorbed or released when salts are dissolved in water.

· Determine the enthalpy of solution for MgSO4, K2SO4, KNO3 and NH4NO3.

· Design and test a hot pack or a cold pack.

Background Information
The process that occurs when an ionic compound (a salt) dissolves in water can release or absorb heat (heat energy is measured in units of joules). The amount of heat released or absorbed when a salt dissolves depends on the difference between crystal lattice energy and the energy gained by solvation of ions from the solid salt.

For example, when sodium hydroxide is dissolved in water, heat is released and the process is exothermic. When ammonium nitrate is dissolved in water, heat is absorbed, and the process is endothermic.

The ability of a salt to release or absorb energy upon solution is called the enthalpy of solution formation, Hsoln. It is important to realize that the enthalpy of solution formation, Hsoln. is not energy from a chemical reaction (HRxn) because there is no chemical change when an ionic compound (a salt) dissolves in water.

Calorimetry
A calorimeter is used to measure the quantity of heat flow from one object (the system) to another (the surroundings). A basic calorimeter is very easy to construct - all that is needed is a couple of Styrofoam coffee cups, a lid, a thermometer, and a way to mix contents of the calorimeter to insure complete reaction and transfer of heat. In this virtual lab, an insulated “Foam Cup” is used to measure the heat transferred when different salts (the system) dissolve into water (the surroundings).

The system (salt) releases heat energy to the surroundings, the water when the system is exothermic. If the mass and the temperature change of the water is known, the specific heat capacity of the water can be used to determine the amount of heat energy transferred. The amount of heat energy absorbed or released by the water (qwater) is calculated by multiplying the mass of water (m) by the specific heat (Cs) of water and the change in temperature of water (T) using the “MCAT” equation:

qwater = mCsT Equation 1

As noted above, heat can released (exothermic) or absorbed (endothermic) when an ionic compound (a salt) dissolves in water. The heat energy released when a salt dissolves (qsoln is exothermic) will be absorbed by the water (qwater) so the water will increase in temperature. Following thermochemistry sign conventions:

qwater = -qsoln Equation 2

The heat energy absorbed when a different salt dissolves (qsoln is endothermic) will be released by the water (qwater) so the water will decrease in temperature. Following thermochemistry sign conventions:

-qwater = qsoln Equation 3

The enthalpy of solution formation, Hsoln is the amount of energy transferred per mole of compound when an ionic compound (a salt) dissolves in water. The enthalpy of solution formation (Hsoln) depends the amount of heat transferred and on the number moles of salt:

Hsoln = Equation 4

Part 1: Determine the heat of solution.
In this experiment you will determine enthalpy of solution formation, Hsoln for four different salts:

MgSO4, K2SO4, KNO3 and NH4NO3.

Procedure
Record details of each step, observations, data, calculations, and results directly into your lab notebook as you do your work.

1. Open the VIRTUAL LAB: Hot/Cold Pack Problem - Part 1: Determine Heat of Solution at: http://chemcollective.org/activities/autograded/117

2. In your lab notebook, prepare a Data Table with the following columns or rows. Complete the table using your collected information from the simulation.

Formula of Salt

Mass of Salt

Initial Temperature

Final Temperature

Temperature Change (T)

3. From the Stockroom, place the following onto the workbench.

· 50 ml graduated cylinder

· Foam Cup 0.2 L (under “Other”)

· 3.0 L carboy of distilled water

· MgSO4

4. Transfer 50.0 mL of DI water to the 50 ml graduated cylinder.

The temperature of water in the graduated cylinder is shown on the left, in the Information box. Record this temperature as the initial temperature of the water to best given precision.

5. Transfer 3 – 5 g of the MgSO4 into the Foam Cup. Record the weight of MgSO4 to best given precision.

6. Click on the graduated cylinder and then drag it onto the Foam Cup. (When you release the mouse, the graduated cylinder will be tipped to show that it is in pour mode.) Enter "50" in the transfer bar and then click pour.

7. Record the highest temperature in the Foam Cup (Final Temperature).

8. Process the Data (Show calculations in your lab notebook)

a) Calculate the amount of heat absorbed by the water.

qwater = mCsT

· Calculate mass (m) from the volume of the solution and the density of water (1.00 g/mL)

· Cs = 4.184 J/g°C.

b) Calculate moles of MgSO4 Used.

c) Calculate the Hsoln of MgSO4.

Note: The autograding features for this assignment are not currently working with the html5 version virtual lab. Your instructor will check your calculation manually.

9. Clear the workbench and repeat Steps 2 – 8 for K2SO4, KNO3 and NH4NO3.

Hot/Cold Pack Problem - Part 2: Design a Hot Pack or a Cold Pack.
10. Open the link: second part at the bottom of the web page: ( http://chemcollective.org/activities/autograded/118 ).

11. Design and test a Hot or a Cold Pack as specified. Details of the Hot/Cold Pack are randomized – each student designs a different Hot/Cold Pack. Follow the instructions below.

12. Calculated the change in temperature from the temperatures given.

T = Tfinal – Tinitial

13. Calculate the heat needed (qwater) to change the temperature.

qwater = mCsT

14. Calculate the moles of ionic compound (salt) needed from Hsoln.

Hsoln =

15. Calculate the grams of salt needed from the moles of salt and molar mass.

16. Subtract the grams of salt needed from the total mass specified (salt plus water) to find the mass of water.

17. Enter your values on the website and Check.

18. If you get an error message, double check your calculations.

19. Currently, “NOTE: THE AUTOGRADING FEATURES FOR THIS ASSIGNMENT ARE NOT CURRENTLY WORKING WITH THE HTML5 VERSION VIRTUAL LAB. THE ANSWERS WILL DIFFER FROM THE RESULTS IN THE LAB.”

20. So if your answer is close submit your data and results for checking by your instructor.

21. If you get the message “Your answer is CORRECT. Good Job.”, print the page and submit as part of your lab report.

Finished Lab Report – Submit on Canvas

Prepare your finished lab report according to the instructions below. Your report should contain the sections below in the exact order they are listed. You should prepare your reports with word processing software. Reports must be typed in 12-point New Times Roman font and spaced 1.5 lines. Reports must be converted to a single pdf file and submitted on Canvas.

Title Information

Experiment title, your name, Date experiment conducted, “Chem 210, Cañada College”.

Section I) The results pages from chemcollective.org.

1. Part 1: Determine the heat of solution.

2. Part 2: Design a Hot Pack/Cold Pack.

Section II) Provide answers to post lab questions in this section.

1. Explain why heat is released and the process is exothermic when magnesium sulfate is dissolved in water.

2. When 5.50 g of Ba(s) is added to 100.00 g of water in a coffee cup calorimeter, the reaction shown below occurs and the temperature of the water rises from 22.00 °C to 61.16 °C. Assume no heat escapes the calorimeter and the specific heat capacity of water is 4.184 J/(g°C). Calculate Hrxn. Show all your work with unit conversion and correct number of significant figures.

Ba(s) + 2H2O(l)  Ba(OH)2(aq) + H2(g) Hreaction = ?

3. Describe the principles of chemistry you learned from this lab.