Summary

Liquids takes the shapes of the container but have fixed volume. Hence apparatus has been devices to measure conveniently and precisely volume of a liquid.

This article describes the idea behind calibration of measuring cylinders and discuss some important apparatus used to measure volume. They apparatus includes:

Measuring Cylinder
Volumetric flasks
beakers
pipettes
burettes
user customized apparatus

Introduction

liquids have no definite shape but assumes the shape of the containers in which they are put in.

One of the methods that can be used to measure volume of a liquid is to pour the liquid into a container of uniform cross-section as shown in figure below.

The volume of the liquid is obtained from the formula:

Volume = cross-section area x height

i.e V = Ah

For the diagram above, area of the cross-section is given as l x b.

This is because the cross-section area of the prism is a rectangle.

Considering the space occupied by the liquid in the container as having shape of a rectangular prism, The volume of the liquid can thus be determined.

using the above diagram, the volume of the liquid in the container = l x b x h=lbh

Relationship between volume and height a liquid

if area of a container is not changing, then increase in volume of the liquid will be reflected in the increase of height of the liquid column.

In the following, we investigate the change how change of liquid height is affected by volume.

Apparatus

Rectangular container
A cylinder

procedure

Take two containers. P with a rectangular base and Q with a cylindrical base.
Container Q is uniformly calibrated as in figure below

pour some water into P and find it’s volume V.
Transfer the water from P to Q and record the height h of water in Q.
Repeat the above procedures for different values of V and record corresponding values of h as in the table below.

Volume V(cm³)	150	200	300	400	500	600	800
height h(cm)	0.97	1.30	1.95	2.60	2.35	3.90	5.20
(v/h)cm²	154.64	153.84	153.85	153.85	153.85	153.85	153.85

a table for Volume against height of a liquid in a uniform container

Draw the graph of V against h

In practice,measuring vessels are made of cylindrical form that have its height calibrated uniformly so that each level of height represents the volume putting in mind that the bottom surface area is fixed and cannot change.

Increase in height shows increase in volume and so the volume that is represented by a particular height can be conveniently indicated on each level of height so that it can always be read off directly without using the formula; V=BaseAarea X height.

Measuring Instruments marked as described above are called measuring cylinders and are commonly used in measuring liquid volumes.

Measuring cylinders are usually made of glass or transparent plastic and graduated incm³ or milliliters(ml).

Measuring cylinders of various capacities

other instruments that can be used to measure volumes includes:

Measuring flasks
pipettes
burettes
beakers

Measuring flasks

Also known as volumetric flasks.

It is commonly used in laboratories to transfer known volumes of liquids.

A volumetric flask is usually calibrated to contain a precise volume at a certain temperature and are used for precise dilutions and preparation of standard solutions. These flasks are usually pear-shaped, with a flat bottom, and made of glass or plastic.

Measuring flask of capacity 500ml with some chemical solution.

pipettes

A pipette is usually used to transport a measured volume of liquid.

It’s name comes from the word pipe because it has a pipe like shape. Mostly it transfers liquids of less than 250ml in volume.

Burettes

A burette is a long graduated glass tube with a tap at lower end and of a fixed capacity with a tapered capillary tube at the tap’s outlet. Typical burettes ranges from 50ml to 500ml in capacity.
stop-cock valve controls the flow of liquid from the burette so that a precise amount of liquid is fetched at any given moment.

The scale of a burette starts from zero at the top and increases downward to the maximum value.

In the diagram above, volume marking markings reads 20ml. This means 20ml of the liquid has been removed from the burette and so the volume left is (50-20)ml = 30ml.

Beaker

A beaker is a cylindrical container with flat bottom. It usually have a small spout (beak) to aid pouring.
Beakers are of various capacities and the largest can carry several litres of liquid.

Unlike a volumetric flask, beaker have a straight curved surface as opposed to sloping sides.

Beakers are usually made of glass (borosilicate glass), but can also be in metal (stainless steel or aluminum) or certain plastics, notably polythene or polypropylene.

Beakers are common lab apparatus.

How to use a measuring cylinder and beaker

When reading volumes, the reading should be taken with the eye positioned with the bottom of meniscus as in figure below.

Conclusion

In this article, we have described various instruments used to measure volumes and highlighted their special features . We have described how to calibrated a measuring cylinder using principles of regular prism. we have discussed some apparatus like beaker,volumetric flasks,pipette and burettes.

Tag: beakers

Measuring Volume of liquids