Chapter 13: Laboratory and Practical SkillsLong Questions with Answers

Explosive chemicals

Chemicals that cause a sudden release of pressure, gas and heat when they experience a sudden shock: picric acid, 2,4-dinitrophenylhydrazine, benzoyl peroxide, nitrocellulose.

Hazards: burns, eye injuries, lung disease and suffocation; flying glass and damage to people, windows and tables.

Precautions: do not move a container you suspect may explode; get the teacher's approval; use the smallest quantity in a fume hood; remove other chemicals; inform others; wear spectacles, gloves and lab coat; keep away from heat; dispose of the waste properly.

Toxic chemicals

A toxic chemical is a poisonous material capable of causing serious health problems: mercury, benzene, chlorine, pesticides, ammonia, hydrogen cyanide.

Hazards: they enter the body by breathing, swallowing or through the skin; they cause headaches, breathing problems, damage to the nervous system, liver and kidneys, cancer (benzene) or death (cyanide).

Precautions: wear gloves and masks; ventilate; keep in the original container; do not work alone; wash hands after use; always work in a fume hood; seek immediate medical aid after exposure.

Why they are needed

A chemistry laboratory is a strict area where rigorous rules must be practised to avoid a deadly accident. A dangerous situation may arise not only for those working there but for the whole area. Proper warning signs ought to be posted so that everyone entering understands and acts accordingly.

Their importance

Toxic chemicals

Mercury, benzene, chlorine, pesticides, ammonia, hydrogen cyanide; also hydrogen sulphide, nitrogen dioxide, carbon monoxide and potassium cyanide.

Effects of a toxic gas in the lab

What to do

Stop the source if safe (close the valve or cap the bottle), switch on fume cupboards and open windows, evacuate everyone upwind, help affected people into fresh air and get medical aid.

1. Stay calm and warn others

Stay calm and do not panic. Alert people in the area and keep everyone away from the spill.

2. Remove sources of ignition and shock

Turn off flames, gas and electrical equipment nearby. Do not move containers or strike the spilled material: shock can set off an explosive.

3. Look after the student

Remove contaminated clothing; wash the skin with plenty of running water (emergency shower) for at least 15 minutes; use the eye wash if the eyes are affected; then seek medical attention.

4. Deal with the spill

Wearing splash goggles, face shield, gloves and apron, ventilate the area; let the teacher contain the spill with a spill kit (an acid is covered with sodium bicarbonate to neutralise it; an explosive is kept wet and not swept dry). Collect the waste for the hazardous waste site.

5. Call for help

Call and assist emergency staff; if a fire or explosion risk grows, evacuate and close doors.

Why chlorine is so dangerous

Chlorine is a toxic, greenish-yellow gas, heavier than air, so it stays near the ground and spreads into houses. It attacks the eyes and lungs and can kill.

Before transport

During transport

If a leak happens

Policy

Strict laws and inspections for transport of hazardous chemicals, public awareness campaigns, and storing large quantities away from residential areas.

Before work

During work

After work

Appropriate safety precautions must be observed at all cost.

Definition

Corrosive chemicals attack living tissues when they come in contact with them. They can be solids, liquids or gases, and attack skin, eyes, the respiratory tract and the intestine.

Examples

Mineral acids including HF, caustic alkalies, glacial acetic acid.

Precautions

Reactive hazards

Reactions not properly performed may cause fires, explosions and dangerous gases. Examples: calcium hydride, Na, Li, azides, picric acid, AlCl₃, benzoyl peroxide. Safety: handle with utmost care, segregate in storage, use a shield and heavy gloves, minimise quantities, tape glass equipment, dispose carefully.

Radiation hazards

High doses damage tissues and organs, causing vomiting, radiation burns, hair loss and radiation syndrome. Alpha/beta emitters are worst inside the body; gamma rays injure from outside. Safety: shield sources, limit exposure time, trained operators only, protective clothing and mask, no skin contact, monitor with badges.

Asphyxiation hazards

A gas or vapour causes unconsciousness or death through suffocation: HCN, CO, N₂, Ar, He, CH₄, CO₂. The person gets no warning. Safety: well-ventilated areas, full lab coat and protective clothing, proper waste disposal, move a victim to fresh air and call trained help.

Definition

Personal protective equipment should be made available to students to face any emergency in the lab; it also reduces exposure to hazardous chemicals. It includes lab coat, protective glasses, face shields, apron, boots and hearing protection.

What each item protects

Choosing PPE

Fire extinguisher

Labs using materials likely to catch fire must have a portable fire extinguisher, which can quickly control a small fire. All students should know where it is, and be trained to use it properly without panic or harm.

Emergency shower

Its location and working must be told to everybody in the lab: it washes off chemical splashes and puts out burning clothes. An eye wash rinses chemicals from the eyes.

Handling an emergency

Periodic drills with compulsory participation prepare students to do this, and check that the equipment works.