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Using a Calorimeter to Determine the Molar Concentration of NaOH Due: February 2nd, 2018 Richard Tsai ID# 20739330 Partner: Nathan TA: Benson Section #001

Introduction: In the study of heat changes during chemical reactions, Calorimetry allows for heat transfer to occur in isolation within a calorimeter at constant pressure. Because no heat is lost or gained externally within an isolated system, we can accurately determine the temperature change in the calorimeter and acquaint that with the heat of reaction. The heat of reaction, q, is equivalent to the enthalpy change, ΔH, and this can be determined by using the equation q=mcΔT where: m is the mass of the substance (unknown) in grams, C is the specific heat capacity of the substance (amount of heat required to raise 1 gram of substance by 1 degree in Joules / K*g) and T being the temperature change (in K). Furthermore, in this experiment the calorimeter itself also retains some heat from the reaction, and therefore the specific heat capacity (C), must be determined. This equation is

q calorimeter =−qhotwater −q coldwater , and can be

seen as the hot water’s original heat – heat gained by cold water is equal to the calorimeter gain. The calorimeter constant (C) must be obtained to comply with accuracy of the results, as it cannot be assumed that all heat of reaction is transferred into the substance, and some is lost to the calorimeter. For determining the heat of solution of a salt, the neutralization of strong electrolytes results in a complete heat transfer from products to the result of H2O, but in the case of weak electrolytes, which only partially dissociate, the reaction occurs in 2 steps (dissociation/ionization, neutralization). The equation used to determine the ΔH soln= qrxn/n, with qrxn equal to the qrxn = -qcal – qsoln. Therefore, the molar enthalpy will just be the heat of reaction/moles of solute (Stathopulos, 2018).

Experimental Procedure: Experimental procedure used for this experiment is outlined in the CHEM 123L lab manual, experiment #2. All steps were followed without deviation (Stathopulos, 2018).

Experimental Observations: Part A Results:

Table #1: Heat of Dissolution of NaOH in a Calorimeter Time (s) Temperature (°C) 10 21.9 20 21.9 30 22.0 40 22.1 50 22.1 60 22.2 Table #2: Temperature of Water After Addition of NaOH Time (min) 2 3 4 5 6 7 8 9 10 11 12 13

Temperature of Soln (°C) 27.0 30.0 31.8 32.0 32.0 32.8 32.0 32.0 31.2 30.8 30.8 31.0

Time (min) 14 15 16 17 18 19 20 21 22 23 24

Mass of Empty Calorimeter: 45.67 g Mass of NaOH Pellets obtained: 10.02 g Initial Temperature of Water: 21.2 °C

Part B Results:

Table #3: Temperature Change of Heated Water

Temperature of Soln (°C) 30.8 31.9 30.8 30.8 31.0 31.0 30.8 30.8 30.2 30.2 30.1

Time (min) 1 2 3

Temperature (°C)

Time (min)

Temperature (°C)

61.0 4 63.7 65.1 5 63.5 65.1 Table #4: Temperature Change of Heated Water + Cold Water

Time (min) 0 1 2 3 4

Temperature (°C) 42.2 39.4 39.2 39.2 39.0

Time (min) 5 6 7 8 9

Temperature (°C) 38.0 38.0 38.2 38.1 38.1

Mass of Calorimeter (with 125ml Heated Water): 139.77 g Mass of Calorimeter (with 250 ml Water): 261.61 g Temperature of Initial Cool H2O: 18.8 °C

Part C Results: Time (s)

5 10 15 20 25 30 35 Time (s)

150 180 210 240 270 300 330 360

Table #5: Temperature Change of HCl + NaOH Temperature (°C) Time (s) Temperature (°C)

24.9 25.0 25.4 25.4 25.4 30.4 25.4

40 45 50 55 60 90 120

25.4 25.4 25.4 25.4 25.4 25.4 25.0

Table #6: Continued Temperature Change of HCl + NaOH Temperature (°C) Time (s) Temperature (°C)

25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0

390 420 450 480 510 540 570 600

25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0

Concentration of HCl: 1.0464 M Temperature of HCl initial: 20.1 °C Temperature of NaOH initial: 20.1 °C

Plot #1: Graphical Analysis of NaOH + HCl 34

32

Tf = 32.02 °C

ΔT=10.12 °C

Temperature in (C)

30

28

26

24

22

Ti=21.9 °C 20

0

200

400

600

800

1000

Time(s)

Results and Calculations: Part A

Calculating Molar Enthalpy for NaOH:

1200

1400

1600

q rxn=−(C cal +msol∗s sol )( ΔT ) q rxn=−(0+

260.02 sol∗4.184 J g∗K

)(10.12° C)

q rxn=−11009.8 J

ΔH =

qrxn n

ΔH =

−11009.8 J 0.2505 mol NaOH

ΔH =−43,951.25

J mol

The molar Enthalpy of the Solution without heat lost due to the calorimeter is -43,950 J/mol.

q rxn=−(C cal +msol∗s sol )( ΔT ) q rxn=−( 22.18+260.02 g∗4.184

J )(10.12 °C) gK

q rxn=−¿ 11234.25 J

ΔH =

qrxn n

ΔH =

−11234.25 J =−44,847.3024 J /mol 0.2505 mol NaOH

The molar Enthalpy of the Solution with heat lost due to the calorimeter is -44850 J/mol.

Part B Calculations and Results: Plot #2: Cool Water + Hot Water 70 Ti Heated Water: 64.60°C

60

ΔT Cold Water: 19.48 °C ΔT Hot Water: 26.32 °C

Temperature (C)

50

Tf Hot and Cold Water: 38.28°C

40

30

20

10

-6

-4

-2

0

0

2

Time (min)

4

6

8

10

Calculating the Heat Capacity of the Calorimeter: ∆ T cold water =19. 4 8 °C ∆ T hot water =−26 .82 °C

M cold water = M H +C − M H =261.61−139.77=121.84 g M H =M cal hot water− M cal= 139.77− 45.67 g=94.1 g

q cal=−q hotwater −q coldwater C cal∗ΔT cal=−(m ∗s∗ ΔT )HW −(m∗ s∗ ΔT )CW

(

C cal∗19.48 °C=− 94.1 g∗4.184

C cal∗19.48 ° C=10362.563 J −9930.49 J

C cal∗19.48 °C= 432.073 J C cal =¿ 22.18 J/°C

Calorimeter constant = 22.18 J/ °C

Specific heat retained of the Calorimeter Specific Heat =heat gained by calorimeter∗mΔT Specific Heat =

)(

J J ∗−26 . 3 2° C − 121.84∗4.184 ∗19. 4 8 ° C g∗K g∗K

431.073 J 45.67 g∗19.48 °C

Specific Heat =¿ 0.485 J/g °C

Specific Heat of the calorimeter is 0.485 J/°Cg

)

Results and Calculations: Part C Plot #3: NaOH + HCl Reaction Heat Curve 32

30

Temperature (°C)

28

26

Tf = 25.4 °C

24

ΔT = 5.3 °C

22

20 Ti = 20.1 °C 0 100

200

300

Time (s)

400

500

600

700

Calculating NaOH Molar Concentration n NaOH = n NaOH =

m NaOH M NaOH 10.02 g NaOH 39.99 g mol of NaOH

n NaOH =0.2506 mol

Molarity of NaOH = M NaOH =

M NaOH =

nNaOH V solution

0.2506 mol NaOH 0.250 L Water

Concentration of NaOH is 1.0024 mol/L

M NaOH =1.0024 mol/ L

q rxn=−(C cal +msol∗s sol )( ΔT ) q rxn=−( 0+250 g∗4.184

J )(5.3° C) gK

q rxn=−5543.8 J

q neutralization=−55.90

kJ mol

(Stathopulos, 2018)

−5543.8 J n NaOH = −55.90 kJ /mol n NaOH =0.09917352 mol NaOH

M NaOH =

nNaOH V solution

M NaOH =

0.09917 mol NaOH 0.1 L

M NaOH =0.9917 mol/ L

Concentration of NaOH = 0.9917 mol/L

q rxn=−(C cal +msol∗s sol )( ΔT ) g∗4.184 J J + 250 ( 22.18 ) ( 5.3 °C ) °C gK

q rxn=−

q rxn=−5661.354 −5 661 .354 J n NaOH = −55.90 kJ /mol n NaOH =0.1013 mol NaOH

M NaOH =

0.1013 mol NaOH =1.013 mol / L 0.1 L

The concentration of NaOH is 1.013 mol/L

Summarized Results: Part A A B B C C C

Table #7: Calculated Results Calculated: Calorimeter Constant Molar Enthalpy of NaOH Not Used Molar Enthalpy of NaOH Used Calorimeter Constant (C) N/A Specific Heat of Calorimeter N/A Molar Concentration of NaOH (M) N/A Molar Concentration of NaOH (M) Not Used Molar Concentration of NaOH (M) Used

Result -43,950 J/mol -44,850 J/mol 22.18 J/°C 0.4850 J/°Cg 1.002 mol/L 0.9917 mol/L 1.013 mol/L

Discussion: Within this experiment, the results were close to theoretical ideal standards. With the calorimeter considered, the molar enthalpy of -44850 kJ/mol NaOH was very close to the desired -44510 kJ/mol NaOH (2). This is a perfect example of which why it is crucial to remember that the

specific heat of the calorimeter is vital to obtain an accurate answer. Some inaccuracies in this experiment include calorimeter leakage, external substances within the chemicals, and assumptions relying on rounding off, such as saying that 1ml of solution is equivalent to 1g, when in reality the density of NaOH and HCl are not exactly 1.00 g/ml but between the 1.0-1.1 g/ml range. Calorimeter spillage would cause the Molarity of the solution to become less accurate, and external substances within the chemicals would absorb extra heat or make the chemical harder to heat up by increasing its specific heat capacity. However, with all it’s inaccuracies, our obtained range of between 0.9917M and 1.013M for NaOH were extremely close to the 1.00M stated in the Lab Manual, and this solidifies that a calorimeter is extremely accurate for liquid substance and chemical reactions requiring heat. Although the calorimeter itself is a great container for isolating chemical reactions, the thermometer proved to be fairly inaccurate as it couldn’t accurately display the temperatures /s as fast as the reaction proceeded, which resulted in a inaccurately presented graph.

Conclusion: In this experiment, we accomplished the purpose of determining the molar concentration of NaOH using a neutralization reaction within a calorimeter. By calculating the molar enthalpy and

taking the heat lost due to the calorimeter into account, we were able to accurately determine the heat released by the NaOH in the neutralization reaction and dividing by the theoretical value of H2O at -55.9 kJ/mol would give us the final molar concentration of NaOH. We obtained values of -43,960 J/mol for molar enthalpy of NaOH without the calorimeter’s heat taken into account, and -44,850 J/mol after taking the Calorimeter’s specific heat into account. Furthermore, we determined the calorimeter constant to be 22.18 J/°C, and the specific heat of it to be 0.4850 J/°Cg. Finally, the Molarity of NaOH was determined to be 1.002 mol/L using only Mass of NaOH and Volume of water, 0.9917 mol/L without taking the calorimeter into account, and finally 1.013 mol/L with the calorimeter considered. These results are precise but are not accurate as they are still a bit off from the desired molarity, and therefore- are not reliable. The fallibility in this experiment is mostly due to the thermometer’s inaccuracy to display temperature at an instantaneous rate, however that being said, this experiment was a complete success and requires little to no improvements.

References:

Stathopulos, S., Chem 123L Laboratory Manual, Winter 2018 Edition ; U of W Department of Chemistry, Ontario, 2018

(2) Petrucci, R. et al., General Chemistry: Principles and Modern Applications, 10th ed. ; Pearson Canada Inc., Ontario, 2011....