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Chem 223 > Lab 12 Chemical Kinetics: Studying a first order reaction > Flashcards

Lab 12 Chemical Kinetics: Studying a first order reaction Flashcards

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1
Q

if you miss recording the time of the color fading what do you do?

A
  • add a few drops of NaOH in excess until the solution is a bright pink
    -     record     the new buret reading
  • record the time that the color fades
  • draw a single line through the data with the missing time. Do not erase

this will work once (maybe twice)
more than twice will require you to start the experiment over.

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2
Q

Procedure

Step 1.

prepare a water bath by filling a trough approx 1/3 full with ____
Carboys of RT water are in the lab….. DO NOT WASTE
place a ________ in the bottom of the trough

A
  • prepare a water bath by filling a trough approx 1/3 full with water
  • Carboys of RT water are in the lab….. DO NOT WASTE
  • place a sheet of white paper in the bottom of the trough
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3
Q

how is the rate of reaction expressed?

A

expressed in terms of change in concentration of reactant or product per unit time.

		e.g. molarity/sec  or  molarity/hr
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4
Q

is the rate of reaction a positive or negative value

A

always expressed as a positive value

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5
Q

Review example data. **Pay attention to all the notes. **

A
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6
Q

procedure

Step 6:
- fill the buret to just above the ____ mL mark with the NaOH stock solution

A
  • fill the buret to just above the 20.0 mL mark with the NaOH stock solution
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7
Q

procedure

Step 7:
- .____ by briefly opening the stopcock and allowing a small amount of the NaOH stock solution to drain into the waste beaker

A

expel any air from the buret tip by briefly opening the stopcock and allowing a small amount of the NaOH stock solution to drain into the waste beaker

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8
Q

what are the safety considerations for Tert-butyl chloride

A

flammable liquid

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9
Q

What is the nuance of adding excess NaOH?

A
  • NaOH is added until the solution just turns a persistent faint pink
  • excess NaOH is then added and the solution turns a brighter pink. let’s say 12 drops.
  • the darker the pink….. the greater the excess of NaOH and the longer the reaction must run in order to consume the excess NaOH
  • because the rate of a reaction decreases over time, if the same amount of excess NaOH (12 drops) is added after each successive data point, the time required to consume the excess NaOH will steadily increase.
  • Therefore slowly decrease the number of drps of excess NaOH added after each successive data point
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10
Q

What do you do after you have collected your data?

A

**1. drain the contents of the buret into the Erienmeyer flask
2. rinse the buret with TWO 20 mL portions of tap water AND TWO 20 mL portions of DI water by allowing the water to drain through the tip into the Erienmeyer flask

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11
Q

the first order rate law can be integrated with respect to time to give:

A
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12
Q

4-5 minutes after the pink color has completely disappeared what do you do?

A
  1. while carefully swirling the solution, slowly add NaOH from the buret until the solution turns a persistent pink color
  2. add **several **drops in excess and re-stopper the flask. Your solution should be a brighter pink color.
  3. record the buret reading +/-0.1 mL
  4. Continue to swirl the solution, record the time (to the nearest second) when the pink color just completely disappears
  5. Repeat this cycle (steps 1-4) until a minimum of 10 data sets have been collected
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13
Q

After having the TA add t-BuCl and starting your timer what do you do?

A

After ~5 minutes (~ means about)

  1. while carefully swirling the solution, slowly add NaOh from the buret until the solution just turns a persistent pink color (make sure the tip of the buret is over the mouth of the Erlenmeyer flask)
  2. add 10-15 drops in excess and re-stopper the flask. your solution should be a brighter pink color.
  3. Record the buret reading in the second line under the column ‘buret reading’ +/-0.1 mL
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14
Q

how many graphs do you have to submit?

A

1
ln[t-BuCl]t vs time(sec)
(the t after the ] is tiny)

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15
Q

the rate of ____ must be determined experimentally

A

the rate of reaction must be determined experimentally

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16
Q

procedure

Step 4:
- using a 100/150 mL beaker, obtain 50 mL ____ solution from the stock. DO NOT TAKE EXTRA

A
  • using a 100/150 mL beaker, obtain 50 mL NaOH solution from the stock. DO NOT TAKE EXTRA
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17
Q

Procedure

Step 2:
- add 100 mL of the 55:50 water:isopropyl alcohol mixture to a ____ 250 mL Erlenmeyer flask from the dispensette

A
  • add 100 mL of the 55:50 water:isopropyl alcohol mixture to a clean dry 250 mL Erlenmeyer flask from the dispensette
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18
Q

after adding 5 drops to the flask what do you do?

A
  1. have the TA add 1.00 mL of pure t-BuCl to the flask. Start your timer. This is t=0
  2. Re-stopper the flask
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19
Q

what is the objective of this lab?

A

determine the first order rate constant for the hydrolysis of tertiary-butyl chloride, t-BuCl

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20
Q

any excess reagents and the contents of the Erlenmeyer flask goes into the ____ waste container

A

any excess reagents and the contents of the Erlenmeyer flask goes into the ORGANIC waste container

21
Q

After recording the buret reading in the second line under ‘buret reading’ what do you do?

A
  1. Continue to swirl the solution, record the time (to the nearest second) when the pink color just completely disappears
  2. The time is recorded in the second line under the column ‘time expired’. DO NOT STOP THE TIMER. RECORD THE TOTAL ELAPSED TIME SINCE THE t-BuCl WAS ADDED.
22
Q

think about what is happening in the flask….

A
  • t-BuCl is added to the flask
  • the t-BuCl starts reacting with the water to produce HCl
  • every 1 mol t-BuCl produces 1 mol HCl (see screenshot)
  • we add NaOH until there is an excess of NaOh, the solutions turns pink
  • as the t-BuCl continues to react, more HCl is produced
  • the HCl consumes the excess NaOH
  • when the NaOH is completely consumed, the solution turns colorless
  • the moles NaOH consumed = the moles of HCl produced = moles of t-BuCl reacted
23
Q

what needs to be submitted next week?

A

… Report Sheet (2 pages:fb)
slope of line and R^2 reported 3 sig figs.
k and t1/2 reported to 2 sig figs. (after the t the 1/2 is small)

… Separate calculations page show the calculation of …
	[t-BuCl]0	 (0 is small)					(3 sig figs)
	[t-BuCl]t for first 2 data points past t=0	(3 sig figs)
	t1/2 (small 1/2 after t)
	[t-BuCl]t and Ratet at 1000 sec 		(2 sig figs) (both t's are small)

… Graph: Excel-generated

	Units and significant figures are important.
24
Q

what must the graph include?

A
  • a title
  • scale, labels and units for the x- and y-axes
  • the best-fit straight line
  • the equation for the line (12 pt font)
  • linear correlation coefficient, R^2 (12 pt font)
25
Q

how do you find the initial concentration of t-BuCl?

A
26
Q

what are the safety considerations for sodium hydroxide 0.250 M

A
  • corrosive to skin
  • can cause series eye damage
  • you must wear goggles at all times
27
Q

What do you add to where the red arrow is pointing?

A

Add 5 drops of phenolphthalein to the Erlenmeyer flask
containing the t-BuCl.

28
Q

the equation (in screenshot) has the form of a ____ line equation

A

the equation has the form of a straight line equation

29
Q

what do you need to do before you leave lab?

A

make sure:
- all equipment has been returned to its proper place
- all waste has been placed in the proper container
- your lab area is clean
- the TA has initialed your lab report sheet

30
Q

review the graph

A
31
Q

A plot of ln[t-BuCl]t vs time will yield a ________ plot where the slope is −k.

A

A plot of ln[t-BuCl]t vs time will yield a** straight line** plot where the slope is −k.

32
Q

what is the calculation to find the concentration of t-BuCl at time t

A
33
Q

the study of the rates of chemical reactions and the mechanisms by which reactants are converted to products

A

Chemical Kinetics

34
Q

nothing but ____ goes down the drain

A

nothing but soapy water goes down the drain

35
Q

what are the safety considerations for Phenolphthalein indicator

A
  • flammable liquid
  • acute toxicity from ingestion
36
Q

procedure

Step 3:
- ____ the flask and place in the water bath

A
  • stopper the flask and place in the water bath
37
Q

expressed in terms of change in concentration of reactant or product per unit time.
e.g. molarity/sec or molarity/hr

A

rate of reaction

38
Q

what is Chemical kinetics?

A

the study of the rates of chemical reactions and the mechanisms by which reactants are converted to products

39
Q

the graph must….

A
  • be created using excel
  • be scaled to a minimum of 4 in tall by 6 in wide
40
Q

after assembling the apparatus what do you do?

A
  1. Record the temperature of the water bath.
    +/-0.1 oC (that o is supposed to be degree symbol)
  2. Record the molarity of the NaOH stock solution.
    Located on the reagent bottle.
  3. Record the initial volume of NaOH in the buret. +/-0.1 mL
    First line in column heading “buret reading”.
41
Q

what are the safety considerations for isopropanol?

A
  • pure liquid
  • highly flammable
  • using 50% water solution can cause minor skin irritation
42
Q

Assemble the apparatus as seen in screenshot

do not remove the ____ from the water bath during the experiment

A

Assemble the apparatus as seen in screenshot

do not remove the flask from the water bath during the experiment

43
Q

Procedure

Step 5:
- Obtain a clean 50 mL ____ and ring stand/clamp
- ____ the buret by adding 5 mL of the NaOH stock solution and allow it to drain through the tip into a waste beaker
- ____ for a second rinse

A
  • Obtain a clean 50 mL buret and ring stand/clamp
  • Rinse the buret by adding 5 mL of the NaOH stock solution and allow it to drain through the tip into a waste beaker
  • Repeat for a second rinse
44
Q

a reaction which occurs with water, HOH

A

hydrolysis

45
Q

hydrolysis

A

a reaction which occurs with water, HOH

46
Q

in our experiment, tert-butyl chloride reacts with water to produce ____

A

tert-butyl alcohol and hydrochloric acid

(see screenshot)

47
Q

the rate of reaction can be expressed in terms of ____

A

the change in concentration of t-BuCl with time

(see screenshot)

48
Q

what is k

A

rate constant

49
Q

knowing that the reaction is first order, what cooresponding rate law can be written?

A

Chem 223 (6 decks)

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