Enthalpy of solution ammonium chloride

Chem Lab

The Fundamentals of Calorimetry Student Name Date

Data
Activity 1
Data Table 1

Time

(min)

Trial 1

Temp. °C

Trial 2

Temp. °C

1

2

3

4

5

6

7

8

9

10

Trial 1

Trial 2

Initial temperature of cold water, Tc

Initial temperature of warm water, Th

Average temperature, Ta

Temperature at time 0 from graph, T0

Heat lost by water in J to calorimeter (Δq)

Heat capacity (C) of calorimeter in J/°C

Average Heat capacity (C) of calorimeter in J/°C

*Note that the Average Heat Capacity (C) calculated above is used in Activities 2 and 3.

1.

1. Create a spreadsheet and graph of the data from Data Table 1, plotting temperature vs. time, and use the Y intercept to find the temperature at time 0 when the two volumes of water are mixed.

a. Insert graph below.

Activities 2 and 3
Data Table 2

5g CaCl2

10g

CaCl2

15g

CaCl2

5g

NH4Cl

10g

NH4Cl

15g

NH4Cl

Mass of water (g)

Mass of salt (g)

Moles of salt

(g x mol/g)

Initial Temperature

(°C)

Ti

Final Temperature

(°C)

Tf

Change in Temperature (°C)

∆T = Tf - Ti

Heat absorbed by the solution (J)

qw = -[cw x mw x ∆T]

Heat Capacity of the Calorimeter (J/°C)

Heat absorbed by the calorimeter (J)

qc = -[C x ∆T]

Enthalpy of solution (J)

∆H = qw + qc

Enthalpy of solution (kJ)

*Note: 1 kJ = 1000 J

Enthalpy/mole of solution (kJ/mol)

∆H/moles of salt

2. Create a spreadsheet and graph for CaCl2 and NH4Cl, using the data from Data Table 2. Plot mass on the X axis and change in temperature on the Y axis for both graphs. The slope will be the change in temperature per gram of salt dissolved.

a. Insert graphs below.

3. What sort of relationship exists between the temperature change and the mass of the solid? Explain why that relationship exists.

4. How do the calculated molar heats of solution for calcium chloride compare to one another? How do the calculated molar heats of solution for ammonium chloride compare to one another?

5. The actual molar enthalpy of solution for calcium chloride is -81.3 kJ/mol, whereas the molar enthalpy of solution of ammonium chloride is 14.8 kJ/mol.

Calculate the average molar enthalpy of solution for each chemical based on your data, and then calculate the percentage error for each.

Percent error is (|Actual – Experimental|/Actual) * 100%

Activity 4
6. Based on the data and graphs for calcium chloride and ammonium chloride, determine which compound to use and what quantity of each compound will be needed to make a chemical hot pack and cold pack. Both packs should be calculated based on using 100 g (100 mL) of water. The hot pack should reach 60 °C, and the cold pack should go down to 3.0 °C from a room temperature of 25 °C.

Hot Pack: Compound needed to achieve 60 °C above room temperature:

Cold Pack: Compound needed to achieve 3.0 °C:

7. What were some potential sources of error in this investigation?

8. Suggest some ways in which the calorimeter or lab protocol could be improved to have lower percentage of errors.

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