Page 54 - Physics

Physics for Secondary Schools

In using a burette the following steps are Common laboratory pipettes are calibrated
to be followed: with 20 cm , 25 cm or 50 cm . The 20 cm 3
3
3
3
1. Pour the liquid into the burette and pipette is used to measure 20 ml of liquid
make sure that it does not pass the while the 25 cm and 50 cm pipettes are
3
3
0 mark at the top. Note down this used to measure 25 ml and 50 ml of liquid,
volume, say V . respectively. This shows that pipettes are
1
2. Note down the value of the amount of specifi cally made for transferring small
liquid you require to use, say V and amounts of liquids from one container to
add it to V to get V . another.
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2
3. Open the tap and let the liquid run
until the level of the liquid reaches V 2. Acti vity 2.5
4. Subtracting V from V gives V. Aim: To measure the volume
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2
of water using a pipette.
Measurement of volume using a pipette Materials: Pipette, beaker, measuring

A pipette is a glass or plastic tube, usually cylinder and water
open on both ends. A pipette is shown in Procedure
Figure 2.31. It is used to transfer a known 1. Pour 100 ml of water into a beaker.
amount of liquid from one container to
another. The liquid is sucked into it until 2. Transfer 25 ml of water from the
beaker to a measuring cylinder using
it reaches the level of the mark shown. a pipette.

3. Observe the meniscus of the water
25 ml in the cylinder.

4. Record the volume of water in the
Figure 2.31: A pipette measuring cylinder.

Sometimes a fl exible rubber bulb is
placed at one end of the pipette to aid Question
in sucking the liquid from a container, How does the original volume of water
shown in Figure 2.32. in the pipette differ with the volume
of water in the measuring cylinder?
Explain.

The volume of water transferred into the
measuring cylinder equals the volume of
the pipette. This is because the volume of

Figure 2.32: A rubber bulb with a pipette a liquid does not change, irrespective of
the apparatus used.

48
Student’s Book Form One

Physics Form 1 Final.indd 48 16/10/2024 20:55