Kin lab - 2 - lab report PDF

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Carleton University CHEM1002A

Experiment 3 Lab Report: Chemical Kinetics (Kin)

Procedure Part 1: Effect of Thiosulphate concentration 1. 45 mL of 0.20 M sodium thiosulphate was measured using the graduated cylinder, and then placed into a 125 mL Erlenmeyer flask. 2. 5.0 mL of 2 M HCl was then added to the Erlenmeyer flask containing the sodium thiosulphate solution and start timing immediately. 3. The flask was then swirled and placed on a paper marked with a cross. 4. Record the time it took for the cross under the Erlenmeyer flask to disappear when viewing from above the flask as solid sulfur began to precipitate. 5. The experiment was then repeated using 40, 30, 20 and 10 mL of 0.20 M sodium thiosulphate solution. For each trial, make up the volume to 45 mL using distilled water before adding 5 mL of 2 M HCl. The time it took the cross to disappear for each trial was then recorded. Part 2: Effect of HCl concentration 1. Add 40 mL of 0.20 M sodium thiosulphate into a 125 mL Erlenmeyer flask. 2. 9 mL of distilled water was then added to the Erlenmeyer flask before adding 1 mL of the 2 M HCL, making a total volume of 50 mL. 3. Swirl the flask containing the mixture and place it on the paper marked with a cross. 4. Record the time it took for the cross under the Erlenmeyer flask to disappear similar to the timing procedure of Step 4 in Part 1. 5. Experiment was then repeated 3 more times using increasing volumes of HCl (1 mL, 2mL 5 mL and 10 mL) while keeping the volume of sodium thiosulphate at a constant (40 mL). For each trial, the volume of distilled water used was adjusted to ensure the total volume was 50 mL. Part 3: Effect of temperature 1. 5 mL of 2 M HCL was combined with 35 mL of distilled water at room temperature before added to the Erlenmeyer flask containing 10 mL 0.20 M sodium thiosulphate. 2. The final temperature of the mixture was measured and the time it took for the cross to disappear was recorded (see Step 4 of Part 1). 3. To determine the effect of temperature on the reaction, this experiment was repeated 4 additional times with distilled water at various temperature. The volume of sodium thiosulphate and HCl (and dH2O) mixture was kept at a constant (10 mL sodium thiosulphate, 35 mL d dH2O, and 5 mL HCl). 4. For each additional trial, 5.0 mL of 2 M HCl was added to 35 mL of distilled water at various temperature (initially 21.5 °C, then 34°C, 40 °C, 46°C, and 53 °C). 5. The time it took for the solutions to turn opaque (disappearance of the cross) for each trial was recorded.

Calculation Effect of thiosulphate concentration Thiosulphate (mL) 45

Distilled water (mL) 0

HCl (mL)

Time (s)

[HCl] M

1/time (s-1)

[S2O3] M

5

20

0.20

0.0500

0.18

40

5

5

24

0.20

0.0417

0.16

30

15

5

34

0.20

0.0294

0.12

20

25

5

60

0.20

0.0167

0.08

10

35

5

110

0.20

0.0091

0.04

Initial concentration of thiosulphate for 45 mL (total volume is 50 mL =0.050L) Trial 2 (Sodium thiosulphate = 40 mL) Concentration = #moles /Volume (L) n=C x V =0.2 M x 0.040L= 0.008 mol =0.008mol / 0.050L=0.16 M

Trial 4 (Sodium thiosulphate = 20 mL) Concentration = #moles /Volume (L) n=C x V =0.2 M x 0.020L= 0.004 mol =0.004mol / 0.050L=0.08 M

Trial 3 (Sodium thiosulphate = 30 mL) Concentration = #moles /Volume (L) n=C x V =0.2 M x 0.030L= 0.006 mol =0.006mol / 0.050L=0.12 M

Trial 5 (Sodium thiosulphate = 10 mL) Concentration = #moles /Volume (L) n=C x V =0.2 M x 0.010L= 0.002 mol =0.002mol / 0.050L=0.04 M

Concentration of HCl =2M x 0.005 L= 0.010 mol =0.010 mol / 0.05 L= 0.20 M The concentration of HCl is 0.20 M and will be constant for this part of the experiment.

Effect of thiosulphate concentration 0.06 0.05

1 / tme

0.04 0.03 0.02 0.01 0

0

1

2

3

4

5

6

7

[S2O3]

Figure 1: Linear relatonship between Concentraton of thiosulphate vs 1/tme

Effect of HCl concentration Thiosulphate (mL) 40

Distilled water (mL) 9

HCl (mL)

Time (s)

1/time (s-1)

[HCl] M

[S2O3] M

1

37

0.02702

0.04

0.16

40

8

2

27

0.03704

0.08

0.16

40

5

5

10

0.10000

0.20

0.16

40

0

10

5

0.20000

0.40

0.16

The total volume is 50mL = 0.050 L Concentration of thiosulphate (40 mL) =0.2M x 0.040L= 0.008 mol =0.008 mol / 0.050 L= 0.16 M The concentration of thiosulphate is 0.16 M and will be constant for this part of the experiment. Trial 4: HCl = 10 mL = 0.010L [HCl] (10 mL) = 2M x 0.010L= 0.020 mol = 0.020 mol/0.050L= 0.400 M

Trial 2: HCl = 2 mL = 0.002L [HCl] (2 mL) = 2M x 0.002L= 0.004 mol = 0.004 mol/0.050L= 0.080 M Trial 3: HCl = 5 mL = 0.005L [HCl] (5 mL) = 2M x 0.005L= 0.010 mol = 0.010 mol/0.050L= 0.200 M

Effect of HCl concentration 0.25

0.2

1 / tme

0.15

0.1

0.05

0 0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

[HCl]

Figure 2: Linear relatonship between Concentraton of HCl vs 1/tme

Effect of Temperature Thiosulphate (mL)

Distilled water (mL)

HCl (mL)

Temperature (C°)

Temperature (K)

Time (s)

ln(1/time)

1/temp

10

35

5

21.5

294.5

93

-4.5326

3.3956 x 10-3

10

35

5

34

307.15

48

-3.8712

3.2557 x 10-3

10

35

5

40

313.15

38

-3.6376

3.1934 x 10-3

10

35

5

46

319.15

28

-3.3322

3.1333 x 10-3

10

35

5

53

326.15

20

-2.9957

3.0661 x 10-3

Effect of Temperature 0

0 f(x) = − 0 x + 0

1 / temp

0

0

0

0

-4.8

-4.6

-4.4

-4.2

-4

-3.8

-3.6

-3.4

-3.2

-3

ln (1/tme)

Figure 3: Linear relatonship between ln (1/tme) vs 1/temp

0 -2.8

From figure 1 and 2 we can see that [S2O3] versus 1/t and [HCl] versus 1/t are both linear, therefore we can conclude that the order of reaction of [S2O3] and [HCl] are 1 m=n=1 therefore, the overall order of reaction: Overall order of reaction = m + n = 1 + 1 = 2 To calculate the activation energy (Ea) for the reaction: From figure 3, it is found that the slope of the figure: Slope = -0.0002 Slope = -Ea/R Ea = -Slope x R = 0.0002 x 8.314 J/K mol = 1.66 x 10-6 KJ/mol Conclusion To sum up this experiment, we found that the reaction order with respect to [S2O3] is 1 as the rate of reaction double when the concentration of thiosulphate doubles. Similarly, the reaction order with respect to [HCl] is also 1 as the rate of reaction would change proportionally to the change of its concentration. Therefore, the overall order for the reaction is 2 (as both reactants have reaction order of 1). The calculated activation energy for the reaction is 1.66 x 10-6 KJ/mol....