Kinetics Lab Discussion

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In your discussion you should make a conclusion and then explain how your experimental results and observations support your conclusion. The points below should help you identify the information you have available from this experiment to support your conclusion. Finish completed lab report by the due date. Be sure to include the following:

    1. a. Purpose. Based upon the introduction in the attached files, what are you trying to find with your experiment?
    2. b. Claim. Based upon the purpose of your experiment, what claim can you make using your experimental evidence?
    3. c. Table(s) of your results. Include expected, experimental, and % error as appropriate.
    4. d. Discussion of your results.
      1. Explain how your experimental results support your claims. Be sure to include graphs that show how you determined k’ and m for Equation 3. Then show how you used the class data to find k, n, and m in Equation 1. Be sure to include:
        • (1)Balanced chemical reactions.
        • (2)The final rate equation with experimentally determined values.
    5. e. Supporting references.

#NOTE: the data sheet will be sent when the work is assigned.

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Experiment 3: Kinetics Question: How do we determine reaction rates? Goals 1. Students understand the concept of the rate of a chemical reaction. 2. Students can determine the rate of a reaction from experimental concentration and time data. 3. Students can determine reaction order based on experimental data. 4. Students can formulate a rate equation and calculate the rate constant from experimental data. Objectives 1. Students can use measure volumes of liquids accurately. 2. Students use a spectrometer to monitor reaction progress. Introduction Background: Phenolphthalein is an indicator used for acid- base titrations. The chemical formula for phenolphthalein is C,H,O, and it is abbreviated used here as H,Ind. The structure for phenolphthalein in an acidic solution is shown in Figure 2. When the pH of a solution changes phenolphthalein can change to the base form shown in Figure 3. This base form, Ind”, is pink in color. In a basic solution the Ind’ form slowly changes to a third form of phenolphthalein IndOH”, shown in Figure 4. OH -10 ОН. OH 0-1 Figure 2. Acid Form - H,Ind, Colorless Figure 3. Base Form - Ind?, Colored Figure 4. Product - IndoH', Colorless You will be studying the rate of this reaction shown in Reaction 1, the change between the colored form Inand the colorless form InOH?. Reaction 1: Ind2- + OH- → IndOH3- You will be studying the rate of this reaction shown in Reaction 1, the change between the colored form In’ and the colorless form InOH?. Reaction 1: Ind2- + OH- IndOH3- Because Ind", the base form, is colored, you can determine the concentration of Ind using a spectrometer. This allows you to follow the concentration of one reactant verses time so that you can determine the rate law for Reaction 1. Integrated Rate Equations: Two Reactants Since there are two reactants in this system, the rate equation for Reaction 1 is a bit complicated. The rate law will be: rate of reaction = k[Ind- Equation 1: 2] M[OH-]" It is possible to simplify Equation 1 by designing the experimental conditions so that the concentration of the hydroxide ion is constant. This is done by using a much higher hydroxide concentration, so that even when the reaction is complete the hydroxide concentration is essentially unchanged. If the hydroxide concentration is constant, we can define a new rate constant k'in Equation 2. This new rate constant is also known as a pseudo rate constant or conditional rate constant: Equation 2: k’ = k[OH-]" This lets us rewrite the rate equation as Equation 3: Equation 3: rate of reaction = k’[Ind2- מן Since Equation 3 only depends upon the concentration of one reactant it is much easier to determine k' and m. Since Ind is colored, we can follow the concentration of the reactant in Equation 3 by measuring the amount of light absorbed by the sample. The change in the absorption with time can be used to find the values of k'and m for Equation 3. For this Experiment, each group will be assigned a different concentration of hydroxide to use for the kinetic study to find k’ and m for that concentration of hydroxide. Then the data for different hydroxide concentrations from each group will be pooled to determine the overall rate law, Equation 1, for the reaction of phenolphthalein according to Reaction 1. The purpose of this experiment is to determine the overall rate law for Reaction 1. Equipment 1. Spectronic 20 spectrophotometers and cuvets 2. Transfer pipets 3. Volumetric flasks 4. Stop watch 5. Disposable Beral pipet 6. Buret Reagents 1.0.15% Phenolphthalein in ethanol 2. 0.300 M Sodium hydroxide Resources 1. “Kinetics of the Fading of Phenolphthalein in Alkaline Solution” by Lois Nicholson, J. Chem. Ed., 66(9), pp725-6. 2. CRC Handbook of Chemistry and Physics - You may use any edition 3. NIOSH Pocket Guide to Chemical Hazards (NPG) - http://www.cdc.gov/niosh/npg/ 4. SIRI MSDS Database - http://siri.org/msds/index.php 5. Chemistry Laboratory Information Profiles, CD-ROM or http://www.acs.org/content/acs/en/about/governance/committ ees/chemicalsafety/safetypractices/clips-list.html 6. Comprehensive Guide to Chemical Resistant Best Gloves - http://www.chemrest.com/ 7. Wikipedia; Phenolphthalein - http://en.wikipedia.org/wiki/Phenolphthalein Safety and Pre-Lab Before starting the experiment, complete the Safety and Pre-Lab template. Procedure You will be using a Spectronic 20 (Spec 20) to measure the absorbance of the basic phenolphthalein reaction solution at the times of measurement. The relationship between absorbance and concentration is shown below in Figure 5. Procedure You will be using a Spectronic 20 (Spec 20) to measure the absorbance of the basic phenolphthalein reaction solution at the times of measurement. The relationship between absorbance and concentration is shown below in Figure 5. 1 0.9 0.8 0.7 y = 330000x 0.6 Absorption (A) 0.5 0.4 0.3 0.2 0.1 0 0.0E+00 5.0E-07 1.0E-06 1.5E-06 2.0E-06 2.5E-06 3.0E-06 3.5E-06 Concentration (M) Figure 5. Absorption of Ind2 at 550 nm in 1.00 cm cell using data experimentally determined by Dr. K. Lukacs of Bryn Mawr College. Kinetic Studies As a group, run four replicates of the following experiment. 1. Prepare 50.00 mL of the [OH) assigned to your group. a. Add 0.300 M NaOH from the buret. Measure the required amount to the nearest 0.1 mL b. Add water to the mark on the volumetric flask. c. Cap the volumetric flask and thoroughly mix the solution by inverting the flask several times. d. Measure and record the temperature of the solution. 2. Obtain a device capable of measuring time to the nearest second. 3. Setup the spectrophotometer a. Set the wavelength to 550 nm. b. Zero the spectrophotometer. c. Blank the spectrophotometer using a cuvet filled with deionized water. 4. Clean the cuvet. a. Wash with soap and water b. Rinse with water c. Rinse with the sample 4. Clean the cuvet. a. Wash with soap and water b. Rinse with water c. Rinse with the sample d. Wipe the outside with a Kimwipe. DO NOT USE ANY OTHER TYPE OF PAPER TOWEL AS IT MAY DAMAGE THE CUVET. e. Handle carefully to avoid fingerprints. 5. Prepare sample solution a. Obtain a clean, dry, 50 mL beaker. b. Measure 7 mL of your sodium hydroxide solution with a graduated cylinder c. Add 7 mL of your sodium hydroxide solution to the beaker. d. Add a single drop of 0.15% phenolphthalein in ethanol to the beaker e. Swirl the solution to mix f. Add solution to the cuvet g. Place the cuvet in the spectrophotometer 6. Start your timer and quickly take your first reading - If the absorbance is greater than 0.6, wait for it to drop to 0.6 before taking your first reading. 7. Make and record readings of absorbance every 30 seconds for five minutes. 8. Discard the phenolphthalein/NaOH solution in the sink and rinse the cuvet with deionized water when you are finished with your measurements. Do not put the cuvet in your drawer.
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Explanation & Answer

Kindly see attached file with the requested lab report.Note that in table 5 I’ve corrected this result with the real one according to your previous calculations. I have no idea why you suddenly changed from 0.002 to 0.0012 in the uploaded pdf file, and if 0.002 was already too low, 0.0012 is even lower ;)

REACTION KINETICS
ACID BASE REACTION OF PHENOLPHTHALEINE
(NAME)
(COURSE)
(DATE)

1. Purpose of the experiment
The purpose of this experiment is the evaluation of the reaction kinetics of the fast acidbase reaction between a pH indicator (phenolphthalein) and hydroxyl anions. In this regard, the
reaction kinetics is evaluated by measuring the variation of the concentration of phenolphthalein
with time by evaluating the color change through absorbance readings. The obtained data are
then used to calculate the rate of reaction, the reaction order, the reaction rate’s equation and the
reaction rate constant.

2. Claims
The absorbance of the solution decreases as the reaction goes on. Such decrease in the
absorbance is related to the decrease in the concentration of Ind2- by the reaction Ind2- + OH- →
IndOH3-.
The reaction rate’s equation can be expressed as
v = k * [Ind2-] * [OH-]

3. Experimental procedure


50 mL of a 0.15 M NaOH solution were prepared from the dilution of a 0.300 M NaOH
stock solution



The spectrophotometer was set to monitor the absorbance of the solution at 550 nm.
Absorbance recordings were zeroed and blanked against a distilled water solution, such
that any absorbance measured is related to the concentration of Ind2- in the solution



A chronometer was used to record the time using a 1 s scale unit



The cuvet was washed thoroughly with soap and water and sequentially rinsed with
distilled water and the phenolphthalein sample



The outside faces of the cuvet were wiped with a Kimwipe, carefully handling it to avoid
any fingerprints



7 ml of the 0.15 M NaOH solution were transferred to a clean, dry, 50 mL beaker



1 drop of a 0.15% phenolphthalein was added to the beaker and the mixture was rapidly
shaken



Approximately 1 mL of the mixture were transferred to the cuvet



The cuvet was placed in the spectrophotometer, and the resulting absorbance of the
solution was monitored every 10 seconds during 5 minutes



...


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