Important rules and practices for F.6 Chemistry
Please keep this paper in theFile Holder of your Practical Report.
General discipline:
In the Chemistry Laboratory, you should
1. wear in white laboratory garn.
2. obey the laboratory regulations issued by the school.
3. hand in laboratory report the day after practical work.
4. keep all report in a file holder uniformly. Name and/or group member,
number of experiment, date of experiment must be specified clearly
on the first page of your report. Single-lined paper sold by the
school is strongly recommended. Inside the report, clear layout of
data/observation, full calculation steps and clear and satisfactory
discussion are important. Do not mind the dirts resulted during
the practical unless they are too large.
5. Attach the manual at the end of your report.
6. Record all readings in your data section in ink immediately. Do not
use correction oil. You should cross out any unwanted matter.
7. Read the manual carefully and consider the planning of the laboratory
work.
Safety precaution
1. The mouth of apparatus should not point to anybody.
2. Wear goggles or ordinary glasses. Contact lens are not recommended.
3. Note any hazardous possibilities.
Basic Technique
1. To clean an apparatus : It is a good practice to clean all glass-wares
at the end of a practical. You will find that it is easy to clean
the glass-wares in the next practical time.
If you are required to clean a piece of glass-ware, You should
(a) clean it by tap water, use a brush if necessary.
(b) rinse it by distilled water twice.
2. De-ionized water is usually used instead of distilled water.
3. To dry an apparatus: If a piece of apparatus has been cleaned before use.
It should be dry after several days and you are safe to use it.
If you are required to dry a piece of wet apparatus such as a
conical flask, there are two convenient and fast methods:
(a) rinse it by using a minimum amount of propanone (acetone),
then dry it by using a hair-dryer.
(b) place it in an oven for about 10 minutes.
4. Use of balance
The following procedures must be obeyed in using any kind of balance.
(1) Clean the pan if there are dirts by using dry and clean cloth; tissue
is not recommended.
(2) Set the balance reading to zero.
(3) Place your chemicals (in a dry, cool suitable container) softly on
the pan.
(5) Weigh the weighing bottle (paper) with chemicals. Record your
reading immediately on your report in ink.
(6) Transfer all the chemicals from the weighing bottle into a suitable
apparatus, e.g. a beaker.
(7) Weigh the weighing bottle again. Record your reading immediately.
(4) Set the balance reading to zero after the removal of your sample.
In the case of using a triple beam balance, it is faster to find the mass
In the following way (e.g. to weigh an object of 252.3 g):
(i) by moving the heaviest weigh (=100 g) you should find that its mass
is between 200 g and 300 g.
(ii) by moving the middle weigh (=10 g, you should find that its mass
is between 250 g and 260 g.
(iii) by moving the lightest weigh (= 1 g), you should find the reading
252.3 g
In the case of using an electronic balance, you should note that whetherthe
balanced is switched on. With the sample on the top-pan, turn the suitable knob
so that the fixeddark level points exactly the middle of the floating light
zone. digits on the left hand side of the light zone gives youthe digits before
decimal point; the floating digits on the right hand side gives you the digits
after the decimal point.
5. To weigh a chemicals:
(a) Rough weighing -- If you are required to weigh a chemicals of accuracy
0.1g or larger in mass, triple beam balance (its accuracy is up to
0.01 g but its precision is only 0.1 g) should be used (Do not
use electronic Top-pan balance). In most cases, a piece of clean
paper is employed to contain the chemicals.
Note: Amount of chemicals required Accepted range of mass
1 g 0.9 g - 1.1 g
2 g 1.8 g - 2.2 g
5 g 4.8 g - 5.2 g
Briefly saying, the accuracy is only 1 decimal place and the range
is 10 % - 20 % of 1 g.
(b) Precise weighing -- it is expressed as "weigh accurately" in the manual.
Use a clean weighing bottle as the container for chemicals. A piece
of clean paper may be used in some cases. You are required to weigh
a chemicals of accuracy up to 2 decimal places.
e.g. Amount of chemicals required Accepted range of mass
0.6 g 0.55 g - 0.60 g
1.0 g 0.95 g - 1.05 g
2.0 g 1.90 g - 2.10 g
5.0 g 4.90 g - 5.10 g
The school electronic top-pan balance reads only 2 decimal places.
6. To dissolve a solid: glass rod is recommended for stirring. Gentle
heating is sometimes required to speed up the dissolution.
7. Total transfer of a solution from a beaker into a conical flask
Use a glass rod to help transfer (avoid sputting). Rinse the beaker by
distilled water from a washing bottle. Washing bottle are restricted
to contain distilled water only. Transfer the washing water into the
conical flask. Rinse the beaker twice.
8. Make up a definite volume of solution by using
a volumetric flask.
(a) Transfer a solution into the V-flask.
(b) Add the washing water into the V-flask ifany.
(c) Add distilled water from a washing bottle.
(d) Swirl the mixture several times.
(e)By the use of a clean dropper, add distilled water to the V-flask until the meniscus of the solution just reaches the graduated line.
(f)Press the stopper by a thumb. Turn the V-flask up side down and then upside for 10 - 15 times. The solution is now ready for use.
9. To fill a burette with a standardized solution
[Similar procedure for filling a pipette with a standardized or unknown
solution]
(a) Clean the burette by tap water and brush if necessary.
(b) Rinse the burette by distilled water twice.
(c) Rinse the clean burette by the standardized solution twice.
Minimum amount of the solution should be used.
You are recommended to add liquid into the burette by using beaker rather
than with the aid of a filter funnel.
10. Use of pipette.
Refer to the no.9 about burette.
A pipette filler should be used to take liquid from a container into the
pipette.
11. The use of indicator solution.
3 - 5 drops are recommended if the amount of it is not specified.
The use of excessive indicator result in the difficulty of determining
the end point.
12. The titration
(a) Take the initial reading of the burette and record it immediately.
The accuracy of the reading should be up to 2 decimal places, e.g.
2.30 cm3
20.04 cm3
Try to estimate the second digit.
(b) Left hand should be used to turn the knob of the burette.
(c) The first cm 3 of solution should be abandoned (To expel air bubbles
in the burette).
(d) Occasional swirling is necessary during titration.
(e) It is safe to add titrant in a fast rate if the colour change at
the portion where the titrant added occupies a small space, or
lasts for a short time. Otherwise, you should add titrant several
drops each time; or even one drop at a time. At the end point, the
colour change is almost permanent.
(f) Record the final reading immediately on your report. Accuracy of
two decimal places is required.
(g) Usually three runs should be carried out and you should get two
concordant results.
12. Maximum volume of liquid inside an apparatus under heating -- do not
exceed one-half of the apparatus.
13. Do not heat any apparatus which is used to measure volume of liquid
accurately. E.g. volumetric flask, cylinder,...
END OF FIRST PART (Updated in May, 2000)