Lesson 2: How to Write an Experimental Part in a Chemistry Lab Report
This
is the second lesson of this course. You can access previous posts of the
course here, Free
Course or Lesson
1 if you have not read them.
The
experimental part in a chemistry lab report is the easiest part to write. However,
if a student does not know what it entails then it is nerve-wracking. So, when
writing this part, your sentences should be in past tense and passive voice. In addition, sometimes you may be required to
list chemicals and instruments you used. In some circumstances, you can just mention
them in prose form. For these reasons, you should always follow the
instructions given by your institution.
Avoid
using personal pronouns such as ‘I’, ‘WE’ etcetera, for example, “We added 5mL
of sodium hydroxide.” Circumvent using these words like the plague if you want
to score high marks in your chemistry lab report. An excellent procedure part
should contain actual steps you carried out in the laboratory, not procedures
in a lab manual.
If
in the lab manual, it is indicated to add two 2ml of 0.1M of sodium hydroxide
(NaOH), but you added 1ml instead of 2ml. In this case, write 1ml of sodium
hydroxide in your lab report. Everything should be in your own words. If you
directly use statements or sentences from your lab manual then you should use
your lab manual as your reference and in-text cites them according to the
provided guidelines. The example below is an extract from a particular lab
manual. Assuming everything was carried out as in the lab manual, I will show
you how to write a good experimental procedure section using this extract.
A lab extract: Titrations of Saturated
Calcium Iodate in Potassium Iodate Solution
(1)
Put about 35mL of 1M HCl into a clean beaker and label it as ‘1M HCl’.
(2)
Obtain about 40mL of Ca (IO3-) 2 in KIO3 in a
clean labeled beaker.
(3)
Prepare a buret for performing titration by rinsing and filling it with the Na2S2O3
standard solution. Record your buret reading.
(4)
Obtain about 200mL of the 0.24M of KI solution in a 400mL of the beaker.
(5)
Obtain a clean, dry 250mL Erlenmeyer flask and add the following:
- Using 50mL graduated cylinder, add 50mL of the KI solution you obtained in the previous step.
- Use a 10mL volumetric pipette to add 10mL of the Ca(IO3)2 in KIO3 solution to KI solution in the Erlenmeyer flask.
- Using a 10mL graduated cylinder, add 10Ml of 1M HCl to the Ca(IO3)2 and KI solution in the Erlenmeyer flask. The solution should be brown at this point.
(6)
Titrate carefully with Na2S2O3 until the
solution turns yellow. When the solution is yellow perform the following:
- Add 10 drops of 1% starch indicator.
- Continue the titration until the solution just turns colorless.
(7)
Record your final buret reading in a table. Repeat steps 4 to 6 twice. Your
readings should be in the range of + or – 0.50mL.
This how to represent the above procedures in your
lab report, assuming there was no change of procedures during lab session:
35ml
of 1M of HCl was placed in a clean beaker and labeled as ‘1M HCL’. 40ml of
calcium iodate in potassium iodate (KIO3) solution was obtained and
placed in a clean labeled beaker. The buret was rinsed and filled with sodium
thiosulfate, followed by recording its initial volume. Consequently, 200ml of
0.240M of KI was obtained and poured into a 400 mL beaker. In addition, a
clean, dry 250mL Erlenmeyer flask was obtained and 50ml of KI was added into it
using a 50mL graduated cylinder. Besides, 10mL of Ca(IO3)2
solution was added to KI solution in a 250mL Erlenmeyer flask using 10.00mL
graduated pipette. Finally, 10mL of HCl was added to the solutions of KI and
Ca(IO3)2 in a 250Ml Erlenmeyer flask using 10.00mL
graduated cylinder. After adding all the solutions, the final of the solutions
in a 250mL was brown. The solution was carefully titrated with sodium thiosulfate
until it turned yellow. When the solution turned yellow, 10 drops of 1% starch
indicator were added to the solution and titration was continued until the
solution turned colorless. Final buret reading was recorded and the process
repeated once more.
As you can see in this example, there is no use
of personal pronouns. Additionally, all sentences are in past tense and there
is a follow in this section. Also, I mentioned the chemicals and apparatus used
in prose form. Therefore, this allows anybody to follow the procedures and
repeat the experiment.
When you are required to
list the materials used in the experiment, you will list them first, following
by discussing them as in the example above. This could have been your list:
- Beaker, 250mL and 400mL
- 10.00mL pipette
- 0.240M of potassium iodide solution
- 250mL Erlenmeyer flasks
- Buret
- Graduated cylinders
- Calcium iodate in KIO3
- 0.0500M sodium thiosulfate
- 1M HCl
- 1% starch solution
Final remarks:
In
your experimental lab section, you should use past tense and avoid using
personal pronouns. You must always follow the instructions provided. Besides,
only include what you did during lab session not what is in the lab procedures.
Comment below if you have any question regarding this lesson.
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