Experiment 3, Rate Law Determination PDF

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1 Experiment 3: Determination of the Rate Law for Two Chemical Reactions Abstract The purpose of this experiment was to determine the rate of reaction for both the iodination of acetone and the reaction taking place between crystal violet and NaOH utilizing the data collected both manually and via the Measurenet system. In part A, two portions of 2.0 mL of acetone, and HCl and 4.0mL of H2O were carefully measured out using a 10mL graduated cylinder and disposable glass pipette, then added to Erlenmeyer flasks. 2.0mL of I2 was then added and a timer started to record the time, in seconds, it took for the reaction to complete, indicated by the colour change of the solution from a yellow-brown tint to clear, and the time recorded. This process was repeated three more times, fluctuating the amount of each solution added, but always summing to 10mL total. The overall rate of reaction was determined to be Rate = 3.40x10-5M-1*s-1 [acetone]1[I2]0[HCl]1 being a second order reaction overall. In part B, crystal violet was added to a cuvette using a bottle top dispenser and the initial absorbance was recorded. 1.0mL of NaOH was then added and inverted as quickly as possible to ensure the best results and its absorbance was calculated and the process was completed a second time for trial 2. This reaction as determined to be a first order reaction, Rate=k’[CV+]1, from the graphs of the collected data. Both methods were effective in determining the overall reaction orders and rate law. Procedure For the experiment procedure, see lab manual (CH111 Laboratory Manual, Winter 2018) pages 52-54, no deviations were made. Wilfrid Laurier University Chemistry Department. Winter 2018. Experiment 3. Determination of the Rate Law for Two Chemical Reactions. Pages 52-54 in Chemistry 111 Lab Manual. Wilfrid Laurier University, ON, Canada. Results Table 1. Qualitative Observations of Part A and B of Determination of the Rate Law for Two Chemical Reactions. Experiment Component Part A

Solution Acetone

Hydrochloric acid

Iodine

Observations Before: Clear, colourless solution During: yellow tinted, translucent solution that slowly lost yellow colour After: Clear, colourless solution Before: Clear, colourless solution During: yellow tinted, translucent solution that slowly lost yellow colour After: Clear, colourless solution Before: Translucent, yellow-brown coloured solution During: yellow tinted, translucent solution that slowly lost yellow colour

2

Part B

Crystal Violet

Sodium hydroxide

After: Clear, colourless solution Before: translucent, bright blue coloured solution During: no observations can be made through colorimeter After: translucent, blue tinted solution Before: Clear, colourless solution During: no observations can be made through colorimeter After: translucent, blue tinted solution

Table 2. Determination of the Rate Law for the Iodination of Acetone. Experimen t

Trial

A

1 2 1 2 1 2 1 2

B C D

Volume of 4.0M acetone (mL) 2.0 2.0 4.0 4.0 2.0 2.0 2.0 2.0

Volume of 1.0M HCl (mL) 2.0 2.0 2.0 2.0 4.0 4.0 2.0 2.0

Volume of 0.0050M I2 / 0.050M KI (mL) 2.0 2.0 2.0 2.0 2.0 2.0 4.0 4.0

Volume Time of DI (s) H 2O (mL) 4.0 188.4 4.0 196.2 2.0 82.2 2.0 87.6 2.0 90.0 2.0 93.6 2.0 366.6 2.0 378.6

Temperature (oC)

21.2 21.2 21.2 21.2 21.1 21.1 21.1 21.1

Table 3. Quantitative Results for Determination of the Rate Law for Crystal Violet with Sodium Hydroxide. Trial 1 Time Absor(s) bance

Trial 2 LN (Absorbance )

0.9379 7 -0.06404 7 0.93611 -0.06602 7.5 0.9346 2 -0.06762 8 0.9328 6 -0.0695 8.5 0.9314 2 -0.07104 9 0.9296 5 -0.07295

1/ (Absorbance )

Time/s

1.066132

4.5

1.068251

5

1.069954

5.5

1.071972

6

1.07363

6.5

1.075674

7

6.5

Absorbance 0.9953 8 0.9931 3 0.9914 5 0.9896 1 0.9881 9 0.9864 5

LN (Absorbance )

1/ Absorbanc e

-0.00463

1.004641

-0.00689

1.006918

-0.00859

1.008624

-0.01044

1.010499

-0.01188

1.011951

-0.01364

1.013736

3 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20 20.5 21

0.9281 8 -0.07453 0.9265 -0.07634 0.9248 1 -0.07817 0.9232 9 -0.07981 0.9215 7 -0.08168 0.9198 8 -0.08351 0.9182 6 -0.08527 0.9166 9 -0.08699 0.9149 9 -0.08884 0.9134 3 -0.09055 0.91177 -0.09237 0.9101 7 -0.09412 0.9085 5 -0.09591 0.9069 4 -0.09768 0.9052 6 -0.09953 0.9036 6 -0.1013 0.9019 8 -0.10316 0.9006 1 -0.10468 0.8990 3 -0.10644 0.897 -0.1087 0.8952 9 -0.11061 0.8934 6 -0.11265 0.8916 6 -0.11467 0.8899 -0.11665

1.077377

7.5

1.079331

8

1.081303

8.5

1.083083

9

1.085105

9.5

1.087098

10

1.089016

10.5

1.090881

11

1.092908

11.5

1.094775 1.096768

12 12.5

1.098696

13

1.100655

13.5

1.102609

14

1.104655

14.5

1.106611

15

1.108672

15.5

1.110359

16

1.11231

16.5

1.114827

17

1.116957

17.5

1.119244 1.121504 1.123722

0.9849 4 0.9826 9 0.9813 1 0.9801 5 0.9786 4

-0.01517

1.01529

-0.01746

1.017615

-0.01887

1.019046

-0.02005

1.020252

-0.02159

1.021826

0.9769 0.9745 4 0.9732 2

-0.02337

1.023646

-0.02579

1.026125

-0.02715

1.027517

0.9714 0.9683 5 0.9677 0.9661 6

-0.02902

1.029442

-0.03216 -0.03283

1.032684 1.033378

-0.03443

1.035025

-0.03532

1.035947

-0.03649

1.037161

-0.03809

1.038821

-0.04017

1.040984

-0.04003

1.040843

-0.04299

1.043929

-0.04498

1.046003

-0.04708

1.048207

-0.04989

1.05116

18

0.9653 0.9641 7 0.9626 3 0.9606 3 0.9607 6 0.9579 2 0.9560 2 0.9540 1 0.9513 3 0.9500 8

-0.05121

1.052543

18.5 19

0.9483 0.9463

-0.05308 -0.05514

1.054519 1.056691

4

21.5 22 22.5 23 23.5 24 24.5

Time (s) 25.5 26 26.5 27 27.5 28 28.5 29 29.5 30 30.5 31

0.8882 5 0.8866 1 0.8849 3 0.8832 6 0.8816 1 0.8799 4 0.8783 4 Trial 1 Absorbance 0.8750 8 0.8734 5 0.8718 7 0.8697 5 0.8684 3 0.8676 5 0.8657 3 0.8640 9 0.8625 3 0.8610 7 0.8567 2 0.8596 7

Questions- Part A

5 0.9445 1 0.9428 2 0.9405 7 0.9389 6 0.9373 9 0.9356 4 0.9339 7 Trial 2

-0.1185

1.125809

19.5

-0.05709

1.05875

-0.12035

1.127892

20

-0.05888

1.060648

-0.12225

1.130033

20.5

-0.06127

1.063185

-0.12414

1.132169

21

-0.06298

1.065008

-0.12601

1.134288

21.5

-0.06466

1.066792

-0.1279

1.136441

22

-0.06652

1.068787

-0.12972

1.138511

22.5

-0.06831

1.070698

LN (Absorbance )

1/ (Absorbance )

LN (Absorbance )

1/ Absorbanc e

Time/s

-0.13344

1.142753

23.5

-0.07172

1.074356

-0.1353

1.144885

24

-0.07369

1.076473

-0.13711

1.14696

24.5

-0.07577

1.078714

-0.13955

1.149756

25

-0.07767

1.080766

-0.14107

1.151503

25.5

-0.07954

1.08279

-0.14197

1.152538

26

-0.14418

1.155095

26.5

-0.14608

1.157287

27

-0.14789

1.15938

27.5

-0.14958

1.161346

28

-0.15464

1.167243

28.5

0.92211 0.9205 8 0.9186 2 0.9168 2 0.9152 6 0.9135 5

-0.08109

1.084469

-0.08275

1.086272

-0.08488

1.088589

-0.08684

1.090727

-0.08855

1.092586

-0.09042

1.094631

-0.15121

1.163237

29

0.91178 -0.09236

1.096756

Absorbance 0.9307 9 0.9289 6 0.9270 3 0.9252 7 0.9235 4

5 1. Calculating the initial concentrations of acetone, I2 and HCl for each of the four experiments.

2. Calculating the rate of reaction for each of the four experiments using the average time of the two trials.

6 Table 4. Summary of the calculations in question 2. Experimen t A B C D

[Acetone] (M) 0.80 1.60 0.80 0.80

[I2] (M)

[HCl] (M)

0.001 0.001 0.001 0.002

0.20 0.20 0.40 0.20

Average Time (s) 192.3 84.9 91.8 372.6

Rate (M/s) 5.02x10-6 1.18 x10-5 1.09 x10-5 5.37 x10-6

7 3. Calculating the reaction orders m, n and p.

8 4. The overall rate law of the iodination of acetone is Rate = k [acetone]1[I2]0[HCl]1 and means that the overall reaction order would be 2nd order, since the Overall Reaction Order = m+n+p. 5. Calculating the rate constant for each experiment and determining the average rate constant of the reaction.

9 Questions- Part B

Absorbance v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 1 1 0.9 0.8

R² = 0.97

Absorbance

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0

50

100

150

200

250

300

350

400

450

Time (s)

1. Figure 1. Absorbance versus Time Graph of Crystal Violet Reaction with Sodium Hydroxide for Trial 1.

LN(Absorbance) v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 1 0 0 -0.2

50 100 f(x) = − 0 x − 0.04 R² = 1

150

200

250

300

350

400

450

-0.4 ln (Absorbance)

-0.6 -0.8 -1 -1.2 -1.4 -1.6

Time (s)

Figure 2. Natural Logarithm of Absorbance versus Time Graph of Crystal Violet Reaction with Sodium Hydroxide for Trial 1.

10

1/(Absorbance) v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 1 5 4.5 4

f(x) = 0.01 x + 0.69 R² = 0.97

3.5

1/Absorbance

3 2.5 2 1.5 1 0.5 0 0

50

100

150

200

250

300

350

400

450

Time (s)

Figure 3. 1/(Absorbance) v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 1.

Absorbance v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 2 1.2 1

Absorbance

0.8

f(x) = − 0 x + 0.9 R² = 0.96

0.6 0.4 0.2 0 0

50

100

150

200

250

300

350

400

450

Time (s)

Figure 4. Absorbance versus Time Graph of Crystal Violet Reaction with Sodium Hydroxide for Trial 2.

11

LN(Absorbance) v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 2 0 -0.2

0 f(x) = −50 0 x + 0.01 100 R² = 1

150

200

250

300

350

400

450

-0.4

ln(Absorbance)

-0.6 -0.8 -1 -1.2 -1.4 -1.6

Time (s)

Figure 5. Natural Logarithm of Absorbance versus Time Graph of Crystal Violet Reaction with Sodium Hydroxide for Trial 2.

1/(Absorbance) v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 2 4.5 4 f(x) = 0.01 x + 0.65 R² = 0.97

3.5

1/Absorbance

3 2.5 2 1.5 1 0.5 0

0

50

100

150

200

250

300

350

400

450

Time (s)

Figure 6. 1/(Absorbance) v. Time of Crystal Violet Reaction with Sodium Hydroxide for Trial 2.

12 2. Based on the R2 values depicted on the graphs, the graph plotted on LN[Absorbance] v. Time(s) is the most linear as the R2 values for both trials is exactly 1 and observably linear. 3. The reaction order with respect to crystal violet is first order because the graph depicting the natural logarithm is the most linear. This is indicative of a first order reaction because first order reactions are depicted linearly on ln(A) versus time graphs (in which they share linear relationship) which is the case for this reaction. Making the overall rate of reaction, Rate=k’[CV+]1. Discussion In the experiment, the data both collected manually and from the Measurenet system was used to determine the rate law of both reactions in the experiment, iodination of acetone, in part A, and the Crystal Violet reaction with Sodium hydroxide, in part B. Part A of the experiment, iodination of acetone, was determined to be a success as acetone and iodine were successfully converted to iodopropanone in the presence of the acid catalyst, HCl. The rate law of the reaction was determined using the method of initial rates. To calculate this, the volume of each of the four solutions added to the reaction, (see Table 2.). Increasing the amount of HCl or iodine present in the solution were the only solutions that make considerable difference to the rate of reaction. Since, HCl is the catalyst in the reaction, increasing the amount in the reaction decreases the rate of reaction and total amount of time the reaction takes to complete. Increasing the amount of iodine present, the rate of reaction increases, increasing the amount of time to complete the reaction. The overall rate order was determined to be 2nd order and the overall rate law being Rate = 3.40x10-5M-1*s-1 [acetone]1[I2]0[HCl]1. In part B of the experiment, the reaction between crystal violet and sodium hydroxide, was successful as the reaction order was calculated using the kinetic results from the Measurenet system (see Table 3.). The kinetics, the absorbance of light by the contents of the cuvette in the colorimeter, of the reaction between crystal violet and sodium hydroxide were recorded via the Measurenet. The order of reaction, with respect to crystal violet, was determined to be first order from observing the most linear graph of the plotted data, making the rate of reaction, Rate=k’[CV+]1. Since the most linear graph was determined to be plotted as “ln[Absorbance] v. Time (s)”, and the first order reaction graphs have a linear relationship on this scale, the reaction order can be concluded as first order. A source of error for part A of the experiment could be the use of graduated cylinders and disposable glass pipettes to measure out the volumes of each solution added. If the incorrect volumes of the solutions are added, the rate of reaction could be influenced and could eventually lead to miscalculations. To prevent this error for occurring, implementation of a micropipette to measure out correct volumes of the solutions and ensure the most accurate results possible.

13

Conclusion The objective of the experiment was to determine, from experimental data, the rate laws and overall reaction orders of two reactions taking place in this experiment. The iodination of acetone was determined to have an overall rate law equalling Rate = 3.40x10-5M-1*s-1 [acetone]1[I2]0[HCl]1 and therefore being a second order reaction. The reaction between crystal violet and sodium hydroxide was determined to be a first order reaction from the data collected via the Measurenet system measuring absorbance.

14 Work Cited Wilfrid Laurier University Chemistry Department. Winter 2018. Experiment 3. Determination of the Rate Law for Two Chemical Reactions. Pages 52-54 in Chemistry 111 Lab Manual. Wilfrid Laurier University, ON, Canada....