Topic 2: Laboratory techniques and safety

Subtopic:      Basic Chemistry Laboratory apparatus and their use

•There are many apparatus that are used for measuring purposes in the laboratory. These include:

•Pipettes

•Burettes

•Measuring cylinders

•Thermometers

•Weighing balances

•Syringes

•Stop watches

a) Pipette

A pipette is a narrow glass tube into which small amounts of liquid are sucked in for transfer to other containers.

A liquid in a pipette adheres to the side of the tube and forms a curved surface called a meniscus.

How to use a pipette

Activity 1

(i) Using your mouth or a pipette filler, suck a liquid from a container to the level above the pipette mark then stop using a finger.

N.B: If sucking is done with your mouth make sure that you control the liquid in such a way that no liquid enters your mouth.

(ii)Regulate the volume of the liquid by gently releasing a finger till the base of the liquid is exactly at the mark on the pipette.

(iii)    Make sure that the pipette is straight  and the eye is directed to the meniscus of the liquid, at a right angle with the pipette (see figure 1.2)

Apparatus for measuring of volumes (Measuring Syringe)

b) Measuring syringe

Alternatively, in the absence of pipette, a medical syringe can be used to measure volumes of liquids. It is cheaply sold in medical shops.

Activity 2

i)  Press down the piston of the syringe to zero mark.

ii)  Insert/dip the syringe into the liquid to be drawn, followed by pulling up the piston to suck the liquid up to the desired mark.

iii) To pour the liquid into another container, slowly press down the piston to empty the liquid.

c) Burette

A burette is a long cylindrical graduated tube with a stop cork near its bottom end. It is commonly used for measuring and dispensing known amounts of liquids during titration. Figure 1.4 shows an example of a burette.

How to use a burette

Activity 3

i.       Always rinse with a solution to be used.

ii.      Fill the burette to the mark.

iii.      Make sure that the nozzle part is filled with the solution.

iv.     To record the volume, make sure that you read at the bottom part of the meniscus as is it is shown in figure 1.5.

 

Equipment for measuring mass (Triple beam balance) cont.

How to use triple beam balance

Activity 4

Step 1

Calibrate the scale by sliding all three sliding masses to the right hand side of the beams. Twist the zero adjustment knob (zeroing screw) until the balance pointer lines up with the fixed zero mark, as shown in figure 1.7.

Step 2

Place the object to be weighed on top of the pan (measurement tray); this will make the pointer to move upward above zero mark. See   Fig 1.8.

Step 3

Slide 100 g beam mass one notch at a time until the pointer drop to or down the zero mark (Make sure the mass is locked in the particular notch). If the pointer lines up with zero mark, record the mass as the mass of your object. If it drops down the zero mark, move it back to the left hand side just one notch.

 For example, if your object weighs 373.3 g, the pointer will drop down the zero mark on the fourth notch when moving 100 g beam mass. Move the mass back to the 3rd notch (ie 300 g). This will make the pointer to move back and point above zero mark.

Step 4

Slide the 10-gram beam mass right one notch at a time.  When the pointer drops below zero mark, move the mass one notch to your left hand side (or right hand side of the beam).

For above example, the pointer will drop down the zero mark on the 8th notch and so you will be supposed to slide it back one notch to 7^thnotch (70 g).

Step 5

Slide the 1-gram beam mass slowly across the front beam. (Note: there are no notches on this beam so keep an eye on the pointer while sliding the mass). Stop sliding when the pointer lines up with zero mark. Considering above example, the pointer will line up at 3.3g. See Fig.1.9.

Heat Sources (Bunsen burner)

Parts of Bunsen burner

Barrel (Chimney)

The barrel is a vertical metal cylinder that is mounted to a base and is the main body of a Bunsen burner. When the burner is activated, flame emerge from the top of the barrel.

Gas inlet

Gas inlet is a metal piece that protrudes from the side of the Bunsen burner at the bottom. When its end is connected to a rubber tube the gas passes from its source to the barrel.

Collar

The collar is a short, hollow cylinder that encircles the lower part of the barrel. Its function is to open or close the air holes. When the air holes are closed, a luminous flame is produced. Half-open or full open air-holes produce a nearly invisible, blue-coloured flame commonly called non-luminous

How to use the Bunsen burner

Activity 6

i)  Connect the rubber tube of a Bunsen burner to the gas tap

ii)  Rotate the collar to close the air holes of the Bunsen burner.

iii) Light a match and immediately open the gas tap and light the gas at the tip of the barrel. A yellow flame will be observed

iv) To get the blue flame, rotate the collar in order to leave the air holes open. This gives a hotter, non-sooty flame suitable for heating purposes

Charcoal burner

In absence of a Bunsen burner, spirit burner, charcoal burner, gas stove, kerosene stove and moto poa stove can be used as heat sources.

Other heat source

                  - Kerosene stoves

                                       -Spirit lamp

 Electric hot plate

Summary

Laboratory is a place for carrying scientific experiments. For experiments to be properly done they need special apparatus and equipment. There are apparatus and equipment for measuring volumes, lengths, temperatures and masses. Also there are apparatus and equipment used as heat sources.  Some equipment and apparatus are delicate and hence, they need to be handled carefully. Proper measuring is needed in order to obtain accurate scientific data. However, in some laboratories there may be no equipment or apparatus for specific purpose. In this case, is improvisation is important.

Resources

South Carolina University and MoEVTZr (2010), Chemistry for Secondary Schools, Form 1&2, Oxford University press Tanzania Ltd, Dar es Salaam.