CHEM 2204

Chemical Laboratory Techniques

Browsing Posts published in February, 2016

DUE: Lab 3

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Practical Assessment 1 will include assessing the following techniques:

  • Technique #2 – Use of a Pipette
  • Technique #4 – Weighing
  • Technique #5 – Use of a Bottle-Top Dispenser
  • Technique #6 – Gravity Filtration, Vacuum Filtration
  • Technique #9 – Rotary Evaporator

On the day of the assessment, you will draw two techniques that you will be assessed on. However, you should prepare for ALL the above listed techniques. In order to be well prepared for your first practical assessment, spend some time to review the techniques we covered. Go to the laboratory page and download the schedule, preparation documents and marking schemes. Come a little bit early and wait outside the lab.

Good luck!

Please check the data for your set.

Set A site data
Set B site data

Using the built-in functions of your SHARP calculator, determine:

  1. Mean or Average, x
  2. Standard deviation, sx
  3. Relative standard deviation, RSD = (sx /x)· 100

for the following set of data: 95, 80, 80, 75, 75, 75, 50

Screen Display
Put calculator in statistic mode 0.
Input 95
(95 M+)
1.
Input 80 two times
(80 M+)
2.

(M+)
3.
Input a number, 75, three times
(75 STO 3 M+)
4.
Input a number, 50, once
(50 M+)
5.
Screen Display
To display Mean
(RCL 4)
75.71428571
To display Standard Deviation
(RCL 5)
13.3630621
To display Relative Standard Deviation
(RCL 5 / RCL 4 * 100)
17.6493273

Therefore, for our data, we can write 75.7 ± 13.4 or 75.7 ± 17.6%

Question: “What should I do if I entered (and stored) a wrong data point on my calculator ? I don’t want to re-enter everything!”
Solution (How to correct after realizing one has stored an incorrect value):
(Courtesy of Vicky Tsui, CENV graduate)

  1. Continue entering the rest of the data points
  2. After that’s done, scroll up with the “up arrow” on the calculator to find the incorrect data value
    • The calculator will scroll through a series of “X=” and the corresponding “N=” entries (i.e. X1=___, N1=___, X2=___, N2=___, etc.)
    • The “X=” fields represent the data points entered, while “N=” denotes the frequency of the corresponding data value (X)
      (for the purpose of the lab, N would equal 1 (default)…. unless if you want to specify the N number of times that a value is repeated)
  3. Once the calculator is displaying the incorrect value, “X= ____” , input the desired correction value and press “M+” to store this number in its place

DONE 😀 (proceed to find the mean, SD, etc.)

To clear data set

Start over!

DUE: Lab 2

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