WORKING WITH LIQUIDS IN LABORATORY

Author: Mr Lam

A lot of chemicals in the laboratory is in liquid form, e.g. acid, water and ethanol.

We need to know or control the volume of the liquids we used.

Therefore, we need to measure the liquid volume precisely. This powerpoint is to show the general procedures in handling liquids

Measuring volume

The equipment you should choose to measure out liquids depends on:

1. Volume to be dispensed2. The accuracy requirement3. The number of times the job must

be repeated.

Examples of measuring equipment

Method Best volume range Accuracy

Usefulness for repetitive

measurment

Pasteur Pipette 1.5mL Low Convenient

Conical Flask/Beaker 25-5000mL Very low Convenient

Measuring cylinder 5-2000mL Medium Convenient

Volumetric flask 5-2000mL High Convenient

Burette 1-100mL High Convenient

Glass Pipette 1-100mL High Convenient

Syringe 0.5-20μL Medium Convenient

Microsyringe 0.5-50μL High Convenient

WeighingAny (depends on accuracy of

balance)Very High Inconvenient

Other considerationsSome special liquids may cause problems

1. High-viscosity liquids are difficult to dispense: need more time for the liquid to transfer (Honey)

2. Organic solvents may evaporate rapidly, making measurements inaccurate: work quickly, seal containers quickly (acetone, ethanol)

3. Solutions prone to frothing are difficult to measure and dispense: avoid forming bubbles, do not transfer quickly (soap solution)

How to hold a Pasteur pipette

Different types of pipettes

Graduated pipette reading from zero to shoulder

Graduated pipette, reading from maximum to tip

Bulb (volumetric) pipette

How to fit pipette filler

Conical Flasks and Beakers

The markings on the these containers are not accurate. They should only be used for measuring volume of solutions, liquids where accuracy is unimportant.

beaker

Conical Flask

Reliable equipment for measuring volume

Burette PipetteVolumetric flask

Microsyringe