Chemistry 1st Paper · Classes 11-12 · Chapter 1 · 1.3

Techniques to Keep the Laboratory, Equipment and Glass Apparatus Clean.

After the experiment a reagent bottle sits on the table, a scrap of filter paper blocks the sink, and drops of water cling to the burette. None of these is a small slip. The rules for keeping a lab clean are short, and each has a reason behind it.

1. The lab, its glass and who looks after it

A school or college chemistry lab usually has two rows of long tables. Each has student desks and a shelf for reagent bottles, plus a water pipe, a basin and a gas pipe for the Bunsen burners. Chemicals live in their own cupboards or shelves. Glassware, and metal and plastic apparatus, each go in separate cupboards too.

The pipette, burette and conical flask are made of pyrex glass, so heat does not break them easily. After washing a burette, pipette, conical flask or funnel, drops of water sticking to the glass tell you it is not clean yet.

The lab is run by the lab assistant, the demonstrator and the chemistry teacher in charge. Even so, every student must leave the lab clean after using it.

2. Where waste and bottles go

During an experiment, broken glass tube, used filter paper and torn paper must never go into the water sink. Put them in the dustbin kept at its fixed place in the lab.

After use, a reagent bottle goes back to its place on the shelf and does not stay on the table. At the end of the experiment, clean the glass tubes you used, leave them on the stand to dry, then arrange them on the table.

See first where each thing goes, and what follows when it goes in the wrong place.

Now put them all in their places in one go.

3. The chemical balance

The Class 11-12 experiments use various glassware, the chemical balance, the Bunsen burner and the thermometer. Career-oriented chemistry adds a pressure canning machine, cans and a cream machine.

The chemical balance weighs pure chemicals accurately. It is a valuable instrument, so learn the method from your teacher before you use it.

Three jobs after using it: wipe the pan with tissue paper or flannel cloth, put the weights back in their places in the weight box, and close the door of the balance box.

4. Washing glassware

An experiment starts with clean glassware. Dirty or opaque glassware cannot be used for a chemical experiment. Usually a wash in tap water is enough.

For oily matter, especially in a burette stopcock, use the chromic acid mixture (K₂Cr₂O₇ and concentrated H₂SO₄) kept in a bottle. Handle it carefully, with gloved hands. Ammonia solution is also used to clean glass apparatus.

To clean a test tube, hold it in your left hand under the tap and work the brush with your right.

Solutions of coloured substances such as iron salts, copper salts, KMnO₄ and K₂Cr₂O₇ stick to the inside of a test tube if left, and take a long time to clean later. So wash it right after use.

Glass tells you itself whether it is clean. Run water down three burettes, then wash each to suit its dirt.

Now test the book's rule on four short cases. The first is about a burette.

The second is about a coloured solution.

The third is about the burette stopcock.

The last is about the balance pan.

Short facts blur together when read once. Answer each of these eight cards in your head, then turn it over.

5. Check yourself

The first question is in the exam's style.

For the second, recall the book's rule.

Think the last one through before you choose.

The whole note on seven cards.

Source: Chemistry 1st Paper, Classes 11-12 (NCTB), Chapter 1 “Safe Use of the Laboratory”, section 1.3.