2b.Lab Assignment Enthalpy of Salts PDF

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Lab Assignment Enthalpy of Salts Purpose The purpose of this lab is to determine the relative q and ∆H values of varying salts to determine relative endothermicity and exothermicity. Group Data Keep all data below. Once you have at least two good trials for a given salt, enter your selected trials (at least 2 per salt) on the group data entry page online. Be sure to select the correct section and lab location. Table 1. Determination of heat and enthalpy of solvation. Trial

Salt

Mass of Salt (g)

Mass of Water (g)

Volume of Water (mL)

Ti (°C)

Tf (°C)

Type of Reaction (endo/exo)

qrxn (J)

ΔH (KJ/mol)

1

CaCl2

1.083

23.967

25.00

18.2

23.3

exo

-534.53

-54.78

2

CaCl2

1.003

24.029

25.00

18.3

23.0

exo

-492.25

-50.45

1

BaCl2

1.010

23.600

25.00

17.8

18.2

exo

-41.19

-8.49

2

BaCl2

1.003

24.461

25.00

17.6

17.9

exo

-31.96

-6.64

1

NaNO3

1.002

24.107

25.00

17.4

15.6

endo

189.10

16.04

2

NaNO3

1.001

24.156

25.00

17.3

15.5

endo

189.46

16.07

Section Data Collect the data from your section and calculate the values to complete the table below. Table 2. Enthalpy of salts. Formula Weight Salt (g/mol)

Type of Reaction (endo/exo)

qrxn (J)

ΔH (KJ/mol)

NH4Cl

53.49

endo

263.65

13.97

KCl

74.55

endo

219.35

16.11

BaCl2

208.23

exo

-38.09

-7.86

NaNO3

84.995

endo

187.64

15.97

KNO3

101.10

endo

253.05

25.24

CaCl2

110.99

exo

-507.67

-54.74

NH4NO3

80.05

endo

280.24

22.18

MgSO4

120.63

exo

-606.61

-72.11

MgCl2

203.30

exo

-57.36

-10.48

Note: Use average qrxn and ΔH values from your section.

Part II Observations  The solution is initially an opaque white solution  Once solution is placed in water, the solution inside the Erlenmeyer flask gradually becomes clear and translucent over time  Presume that the heat from the surrounding water causes the solution to turn clear  After the flask is pulled out of the surrounding heated water, the solution inside the Erlenmeyer flask recrystallized into an opaque white crystalline solid. o The crystals form a fracturing pattern or a lattice pattern.

Complete the following tables for your endothermic and exothermic salts. These are meant to help you recognize patterns. Look at your data above and rank the salts. List the first, second, and third salts for each in the boxes below. For example, if NH 4Cl has the highest value for qrxn and KCl is second, then write "NH 4Cl" under highest and "KCl" under second for that row. Table 3. Salt rankings. Highest

Second

Third

EXOTHERMIC Rankings

Average qrxn

MgSO4

CaCl2

MgCl2

Average ΔH

MgSO4

CaCl2

MgCl2

ENDOTHERMIC Rankings

Average qrxn

NH4NO3

NH4Cl

KNO3

Average ΔH

KNO3

NH4NO3

KCl

Calculations Include at least one example of each calculation required for the Enthalpy of Salts In-Lab Assignment. You do not need to include an example for the calculation of averages. Calculating CaCl2 -q(rxn): (1.083g CaCl2 + 23.967g H2O)*(4.184 J/g°C)*(23.3°C-18.2°C) = 534.526J Calculating CaCl2 ∆H rxn: moles of CaCl2 = (1.083 g CaCl2 / 110.99 g/mol CaCl2) = 0.00975 mol CaCl2; (-534.526J/0.00975 mol)*(1/1000) = 54.78 kJ/mol...