Chemistry · Class 9-10 · Chapter 1 · The idea of chemistry
Care in the laboratory.
A laboratory is not a frightening place, it is a place with rules. Nearly every accident comes from one of three things: handling something you have not identified, hurrying, and not wearing the protection. All three can be headed off in advance, and heading them off is what this section is for.
1. The pictures on the bottle
Why is there a picture on a bottle of chemicals rather than a sentence? Because a picture can be read in a second, without knowing the language, in a hurry, and from across the room. The first piece of information is the shape: a red bordered diamond standing on its point means this bottle carries a chemical hazard, and the drawing inside says which one.
Tap the eight symbols one at a time. Each one comes with its meaning, an example, and what it asks you to do.
hazard symbolspick a symbol
What each picture is saying
Flammable. A flame. It catches fire easily. Examples: alcohol, ether, natural gas. What it asks: keep it away from flame and heat, always.
Explosive. An exploding bomb. A knock, a rub or heat can set off a violent explosion. Examples: TNT, nitroglycerine, organic peroxides.
Toxic. A skull and crossbones. Even a small amount does serious harm on the skin or breathed in. Examples: benzene, methanol.
Corrosive. A liquid eating into a hand and into a metal plate. On skin it burns, breathed in it damages. Examples: HCl, concentrated H₂SO₄, a solution of NaOH.
Irritant, or harmful. An exclamation mark. It irritates skin, eyes or airways. Examples: cement dust, a dilute acid. The least alarming looking symbol is the one most often ignored.
Health hazard. A burst inside a chest. Nothing may happen at the time, and over years it can cause cancer or damage the airways. Examples: benzene, toluene, xylene.
Harmful to the environment. A dead fish and a dead tree. It harms life in water and on land. Examples: heavy metals like lead, mercury and arsenic. What it asks: never pour it away anywhere convenient, and recover and reuse it where that can be done.
Radioactive. A three bladed mark called the trefoil. It gives off harmful radiation, and over time can cause cancer or disability. Examples: uranium, radium. Notice that it is not a diamond: the others are red bordered diamonds, and the trefoil is a separate international sign altogether, so the shape alone identifies it.
All eight. The best way to keep them is to match the picture to the harm: a flame means fire, a skull means poison, an eaten hand means a burn, a dead fish means the environment.
The symbols are drawn by hand, so they will not match a printed label exactly. The shape and the picture inside it are what to recognise.
check yourselfpick one answer
The picture on the bottle
A bottle carries a picture of liquid eating into a hand and a metal plate. What kind of substance is it, and what is an example?
Flammable is a flame, not an eaten hand. Ether really is flammable, but this is a different picture.
Right. A hand and a metal plate being eaten away means corrosive: a burn on skin, damage if breathed in. Concentrated H₂SO₄, HCl and a solution of NaOH are all examples.
Radioactive is the trefoil, a separate three bladed mark. It does not even sit inside a diamond.
Explosive is an exploding bomb. TNT is indeed explosive, but the picture in the question is about corrosion.
2. Learn the room first
The most useful thing to do on your first day in a laboratory is not an experiment. It is to look around the room and commit a few positions to memory: the fire extinguisher, the bucket of sand, the eyewash and the tap, the first aid box, the fume hood, and the way out. Because when one of them is needed there is no time left for looking.
There are ten points on the drawing below. Six of them are the things whose position you need to know. The other four are mistakes, the kind you can check yourself for before starting any piece of work. Find all ten.
the roomtap each point
What is where in a laboratory
1. The fire extinguisher. If there is a fire, this is where it comes from. On your first day, look and see where it is mounted.
2. The bucket of sand. For a small fire, and above all where water would not be safe, sand is thrown over it to cut the air off.
3. The eyewash and the tap. This is where you come if a chemical reaches your eyes or your skin, which is why the space around the sink has to stay clear. Do not block the way to it with bottles or bags.
4. The first aid box. You need to know where it is, and who opens it. Whatever happens, the first thing to do is tell your teacher, not to handle it yourself.
5. The fume hood. Work that gives off a volatile, foul smelling or poisonous gas does not belong on an open bench. It belongs inside the hood, which draws the air away and out.
6. The way out. Knowing in advance which way you would leave takes most of the panic out of leaving. Ask your teacher where your school expects everyone to gather, too.
7. Goggles pushed up on the forehead. Goggles on the forehead leave the eyes bare, and one splashed drop is enough. They stay over the eyes until the work is finished.
8. Loose hair. Long hair left loose can reach a burner flame or trail into a chemical. Tie it back. Very loose or hanging clothes carry the same risk.
9. An open bottle. An open bottle lets vapour out, spills everything if it goes over, and if the stoppers get swapped it can mix two chemicals. Put the stopper back as soon as you have poured, and never return what you did not use to the bottle.
10. A burner left alight. If you are not using it, put the burner out, and close the gas tap before you leave the bench. If anything flammable is nearby, move that away from the flame first.
All ten. Six of them are positions to remember: extinguisher, sand, eyewash, first aid box, fume hood and the way out. The other four are habits, and you can check yourself for all four before you start anything.
The room is a hand drawn model. In your own school laboratory these things will be somewhere else, so go and look at your own room.
3. Before you start
Protective equipment is not a formality. Each piece has a definite job, and each one protects a different part of you. Pick out the ones you would need from the list below. One thing in the list is not protective equipment at all.
put it ontap to put it on
What you do not start without
The apron. It protects your body and your clothes when an acid or an alkali splashes. It comes off before you leave the room, because whatever splashed is on it.
Gloves. They keep corrosive and poisonous chemicals off your hands. Do not touch your face, your eyes or your phone with a gloved hand, because that is how the chemical gets there.
Safety goggles. They save your eyes from a single splashed drop, and damage to an eye is one of the injuries that does not come back. Pushed up on the forehead they do nothing at all.
The mask. It filters some of a poisonous or foul smelling gas. Even so, work with a volatile chemical belongs in the fume hood, not on an open bench with a mask on.
Hair tied back. Not a piece of equipment, and still on the list. Long hair left loose can reach a burner flame or trail into a chemical. Very loose or hanging clothes are the same risk.
Headphones. This is not protective equipment; it is the opposite. With headphones on you cannot hear a warning or an instruction, so the risk goes up. Safety equipment is a definite list, not whatever feels sensible.
All six seen, and five of them are real. The apron for the body, gloves for the hands, goggles for the eyes, the mask for breathing, and tied hair for the flame. The sixth protects nothing.
4. Ten habits
The rules do not stick when they are read as a long list, and they do stick when each one has to be judged right or wrong. Sort the ten habits below into two boxes.
sort themchip, then bin
Right or wrong
Pick up a chip, then drop it in a bin.
Right. Next one.
Not there. Ask: does this open a route for something to reach your body or the air?
All in place. The most dangerous of the ten is pouring water into acid: the water can boil at once and throw acid out with it. The rule in one line: acid into water, slowly, stirring.
5. One bench, two ways
The last habit is the easiest and the most often skipped: look at your own bench once before you start. Drag the handle. The same room, the same bench, the same person, and five things different.
before and afterdrag the handle, find five
One bench, two ways
The five: goggles on the forehead or over the eyes, hair loose or tied, no apron or an apron, the bottle open or stoppered, the burner alight or out. You can check yourself for all five, before you start, in about ten seconds.
The drawing is a hand drawn model, not a picture of any particular laboratory.
check yourselfpick one answer
The three bladed mark
What is the international sign for radioactivity called?
The red bordered diamonds are the GHS symbols, and the radiation sign is not one of that family. Its shape alone sets it apart, which is the point of it.
Right. The three bladed mark is the trefoil. The other chemical hazard symbols are red bordered diamonds standing on a point; the trefoil is a separate international sign altogether.
The biohazard sign also has three parts and does look a little similar, but it stands for a biological hazard such as an infectious organism, not for radiation.
Crossed bones belong to the skull symbol, which means poison. There are no bones in the radiation sign.
6. And whatever happens
Almost all of the above is about preventing an accident. If one happens anyway, the most important thing to do is a single item short enough to memorise: tell your teacher at once. It is the accident hidden because it seemed small that turns into the large one. A spill, broken glass, something on your skin, a smell of gas: the first move is to say so.
The second thing to do is to do today, before anything happens: ask your teacher what the rules of your own laboratory are. Where everything is kept, who does what if something goes wrong, and where everyone gathers if the room has to be cleared. These differ from school to school, and the only way to know is to ask.
The previous section said how a question gets answered. This one gives the condition under which that search can be done safely. Neither is much use without the other, and this is exactly where the chapter ends.
check yourselfpick one answer
A bottle with no label
There is a bottle on the bench with no label on it and a clear liquid inside. What is the right thing to do?
Never smell or taste a chemical: that is the rule, and it is firmest of all for something unidentified. If it is poisonous or volatile, one breath is enough.
A great many things look clear. Concentrated acid, alcohol and ether are all colourless. There is no identifying a chemical by looking at it.
Right. No label means it is unidentified, and there is no handling an unidentified chemical. Saying so is the only safe move, and what happens next is the teacher's decision.
An unidentified chemical does not go down the sink. Some react with whatever is already in the drain, and some damage the environment directly. How to dispose of it is also the teacher's call.