# CHEMISTRY

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Solvent Extraction, Pre-lab page 2

(e) How would the results differ if you added sodium *p*-toluate instead of *p*-toluic acid to the

two-layer mixture of diethyl ether and water?

4. How many milliliters of 3.0 M HCl would be required to neutralize 30. mL of 0.50 M

NaOH? (**Show your work**). (hint: this is a general chemistry question! Remember that the

acid HCl and the base NaOH react in a 1:1 molar ratio. The number of moles of acid need to

equal the number of moles of base to effect complete neutralization).

5. Briefly explain how you will isolate *p*-toluic acid after it is extracted it into NaOH solution.

6. Write the equation for the chemical reaction of the toluate ion that will occur when you

add HCl solution to the NaOH extract in part 3.

SN1 Reaction: A Kinetic study

**Post-Laboratory Questions **(attach your responses on a separate sheet)

1. From the experimental data, prepare a table of the following values. Record all calculated

results to the proper number of significant figures. Note that V and V¥ are the ** total **volumes of

NaOH solution delivered; they are not burette readings (unless, of course, your initial buret

reading was 0.00 mL). Base your calculations on the actual value of V¥ that you measured in lab

– **not the theoretical value**! Time, t, is the elapsed time in seconds (its OK to use minutes if you

prefer). Use Equation 10 to calculate the values of *k*.

** t (sec) V (mL) V/V**¥

**¥**

*(1 – V/V***¥**

*) ln(1 – V/V*

*)*

*k*2. Prepare a graph of ln(1 – V/V¥*) *versus time, t. Using a computer program or a graphing

calculator, determine the best straight line through your data points. (See the supplement to this

lab for detailed instructions on how to determine best fit if you are unfamiliar with this process).

**This graph should be properly labeled and drawn to scale**. Do the data support the SN1

mechanism? Briefly explain.

3. Calculate the value of k from the slope of the line from the graph in 2.

4. Using the values of k which you determined above (in question #1), calculate the average

value of *k, *and estimate its uncertainty. One way to estimate its uncertainty is to

(1) calculate an average value of *k*

(2) calculate the absolute value of the deviation of each value from the average value

(3) calculate the average of these deviations.

Prepare a table which shows the deviation for each datum, and report the average value of *k *and

the average deviation. It may be convenient for you to include these data in the table you prepare

for post-lab question #1, above.

Note: What you are doing here is a standard statistical way of measuring *reproducibility*.

Theoretically, the value of k should be the same for all trials. In practice, however, you almost

certainly will observe some variation in the calculated values of k. The average deviation is a

way of expressing in a single number how much variability you have in your data. Low average

deviations mean your numbers are all close together; high average deviation means you have a

lot of “noise” or “scatter” in your data.

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**Pre-Laboratory Assignment **SN1 Reaction: A Kinetic Study

Name ________________________________________________________________

*Note: you may wish to copy this pre-lab before you submit it. (The results of pre-lab question*

*#2 will be helpful for your lab calculations)*.

1. Describe briefly the hazards associated with the reaction mixture and the safety precautions

you must take when performing the experiment.

2. Assume that you use 1.00 mL of 2-chloro-2-methylpropane. Calculate the following

quantities. **Be sure to show your calculations; you will NOT receive credit if work is not**

**shown!**

a. the number of moles of 2-chloro-2-methylpropane used. The density of the liquid is

0.851 g/mL.

b. the number of moles of HCl produced by complete solvolysis of 1.00 mL of 2-chloro-2-

methylpropane.

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SN1 Reaction: A Kinetic Study, Pre-lab page 2

c. the volume in milliliters of 0.350 M NaOH required to neutralize the HCl produced by

complete solvolysis of 1.00 mL of 2-chloro-2-methylpropane. (This is referred to as V¥ in your

lab manual).

d. the volume in milliliters of 0.350M NaOH required to neutralize the HCI produced when

solvolysis of 1.00 mL of 2-chloro-2-methylpropane is 50% complete. (This is referred to

as V50% in your lab manual; the volume of base consumed when the reaction is 50%

complete).

Note: you may wish to record the values of V¥ and V50% separately before you turn in your

pre-laboratory assignment; you will need these values during the experiment.

Studying SN1 Reactions:

Nucleophilic Substitution at

Saturated Carbon