9th Class Chemistry · Punjab Board · Complete learning guide

Chapter 13Laboratory and Practical Skills

Every topic, every MCQ and every exercise question, explained step by step in simple language. Written for the Punjab Board new-syllabus Chemistry book, English medium.

Start reading Try the 24 MCQs Take the self-test

What you will find inside

Part 1

Learn the chapter

6 topics with diagrams

Part 2

MCQs fully solved

24 MCQs with reasoning

Part 3

Short questions

42 exam-ready answers

Comprehensive questions

11 detailed long answers

Part 6

Revision & self-test

Key facts, key terms, test

On their own page:Chapter 13 MCQs Chapter 13 Short Questions Chapter 13 Long Questions

How to use this guide

Read Part 1 slowly. Do the worked examples yourself on paper, then compare.
Try each MCQ before opening its answer, then read why the wrong options are wrong.
Learn the short answers in your own words, then write the long answers from memory.
Finish with the self-test in Part 6. A wrong answer tells you which topic to read again.

Part 1of 6

Learn the Chapter

Read this first. Everything in the exercises comes from these topics.

1The chemistry laboratory and its rules
2Flammable and explosive hazards
3Corrosive and toxic hazards
4Reactive, radiation and asphyxiation hazards
5Hazard signs
6PPE, fire extinguisher and emergencies

Topic 1

The chemistry laboratory and its rules

A chemistry laboratory is a place where a student is trained to observe the physical and chemical characteristics of substances by following definite procedures. Before starting work, get familiar with the layout of the lab and the fittings on the tables and side shelves.

A school chemistry lab: know where the exits, fire extinguisher, emergency shower, eye wash and fume cupboard are.

General rules (from the book)

Conduct yourself in a responsible manner at all times; do not work alone.
Perform experiments in the presence of the lab instructor and staff.
Check all equipment before use and work out the potential hazards before beginning.
Observe appropriate safety precautions at all cost.
No crowding; stay at your own work place at a safe distance from others.
Do not bring any food items into the lab.
Never taste or smell any compound or gas. If you must smell a gas, waft the fumes towards your nose.

Wafting: wave the vapour towards your nose; never sniff directly.

Waste disposal

Do not pour chemicals down the drains and do not use the sewer for chemical waste. Keep sink traps and floor drains clean. Non-hazardous waste may go into the sewer or trash bin; acids and bases are first neutralised and then flushed to the sewer; hazardous waste is transported to a hazardous waste disposal site.

Misuse and mishandling of chemicals may create serious problems. Chemicals that can threaten safety include cleaning agents, disinfectants, solvents, paints, compressed gas cylinders, mineral acids and carcinogenic chemicals. Recognising the common hazards helps to identify and minimise them.

Hazard type	What it does	Examples (from the book)
Flammable	catches fire easily (flashpoint near room temperature)	ether, methylated spirit, benzene, acetone, petrol
Explosive	sudden release of pressure, gas and heat on shock	picric acid, 2,4-dinitrophenylhydrazine, benzoyl peroxide, nitrocellulose
Corrosive	attacks living tissue	mineral acids incl. HF, caustic alkalies, glacial acetic acid
Toxic	poisonous	mercury, benzene, chlorine, pesticides, ammonia, HCN
Reactive	violent reactions, fires, dangerous gases	calcium hydride, Na, Li, azides, picric acid, AlCl₃, benzoyl peroxide
Radiation	damages tissues and organs	alpha, beta and gamma sources, X-rays
Asphyxiation	suffocation by lack of oxygen	HCN, CO, N₂, Ar, He, CH₄, CO₂

Topic 2

Flammable and explosive hazards

Working in the laboratory requires great care, responsible behaviour and good attention, especially with delicate instruments, hazardous chemicals and open flames. Flammable and explosive chemicals not handled safely can cause burns, eye injuries, lung disease and suffocation.

Definition

Explosive chemicals

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

Definition

Flammable chemicals

Chemicals or mixtures which have a flashpoint around room temperature. Examples: ethers, methylated spirit, benzene, acetone, petrol.

Definition

Flashpoint

The lowest temperature at which a liquid gives enough vapour to catch fire from a flame or spark.

If you come across a chemical that you suspect may explode, do not attempt to move the container, to avoid shock. Explosives can damage people, windows and tables. Avoid using a hazardous chemical; look for an alternative.

Safety instructions

Obtain prior approval from your teacher.
Always use the smallest quantity of the chemical.
Always conduct the experiment in a fume hood.
Remove all other chemicals and apparatus around you.
Inform other people working with you.
Always wear safety spectacles, gloves and a lab coat.
Keep flammable compounds away from heat sources.
Pour flammable liquids very carefully.
Properly dispose of any hazardous waste.
Do not store flammable liquids in a refrigerator.

Why not the fridge?

An ordinary refrigerator has sparks inside (thermostat switch, light). Vapour of a flammable liquid collects in the closed box and a spark can set off an explosion; only special spark-proof refrigerators may hold flammables.

Topic 3

Corrosive and toxic hazards

Definition

Corrosive chemicals

Chemicals that 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 (NaOH, KOH), glacial acetic acid. Whenever you work with corrosive chemicals, wear splash goggles instead of safety glasses and use a face shield.

Safety precautions

Use corrosive chemicals in a fume cupboard to avoid breathing corrosive vapours.
While mixing concentrated acids with water, always add acid slowly to water and not vice versa.
Ensure an eye wash and emergency shower are available.
Wash the affected area with soap and water and seek medical attention in an emergency.

Add acid to water, slowly, with stirring; never water to acid.

Diluting a concentrated acid releases a lot of heat. If water is poured into acid, the first drops boil instantly on the acid surface and spit hot acid out. Acid added slowly to a large volume of water is diluted at once and the heat spreads through the water.

Toxic chemicals

Definition

Toxic chemical

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

Safety instructions

Wear gloves, masks or other protective devices.
Keep the work area well ventilated.
Keep toxic chemicals in their original container.
Do not work alone.
Wash your hands with soap and water after finishing.
Always work in a fume hood, because toxic vapours can form during an experiment.
Seek immediate medical aid if you think you have been exposed to a poisonous substance.

Topic 4

Reactive, radiation and asphyxiation hazards

Reactive chemicals

The reactivity of chemicals is vital for producing many chemicals, medicines and food products. When reactions are not performed properly they may cause fires and explosions, or give off dangerous gases, damaging life and property. Examples: calcium hydride, Na, Li, azides, picric acid, AlCl₃, benzoyl peroxide.

Safety instructions

Handle reactive chemicals with utmost care; segregate them from other chemicals in storage.
Take measures before reacting them; use a shield and heavy gloves.
Minimise the quantity used.
Shield glass equipment by wrapping it with tape.
Carefully dispose of every dangerous material after use.

Note

Sodium and lithium are stored under kerosene oil, away from water and air.

Radiation hazards

A high dose of radiation can damage tissues and organs and cause vomiting, radiation burns, hair loss and radiation syndrome. Alpha and beta emitters do extreme damage when inhaled or injected; gamma rays cause external injuries; medical X-rays are ionising radiation that can affect living tissues.

Safety instructions

Keep radioactive sources shielded.
Avoid prolonged exposure.
Stay inside: walls and ceilings protect you from radiation fall-out.
Never operate radiation equipment without sufficient training.
Wear protective clothing and a face mask.
Avoid contact of the material with bare skin.
Monitor exposure with badges.

Asphyxiation hazards

Definition

Asphyxiation hazard

A hazard in which a gas or vapour can cause unconsciousness or death through suffocation.

A sufficient level of oxygen is essential for normal breathing. The exposed person has no warning and cannot realise that the oxygen level has become low; they may feel rapid breathing, rapid heart rate, nausea and convulsions. Examples: hydrogen cyanide, carbon monoxide, nitrogen, argon, helium, methane and carbon dioxide.

Simple asphyxiants	Chemical asphyxiants
push oxygen out of the air (dilute it)	stop the body using oxygen
N₂, Ar, He, CH₄, CO₂	CO (blocks haemoglobin), HCN (blocks cells)

Safety instructions

Store and use asphyxiants in well-ventilated areas.
Wear a full lab coat, glasses, gloves, long trousers and closed-toed shoes.
Dispose of waste strictly according to instructions.
If exposed, wash the exposed part with running water and seek medical attention.
If inhaled, move the patient out of the contaminated area and call a trained person.

Topic 5

Hazard signs

A chemistry laboratory is a strict area where rigorous rules must be practised to avoid a deadly accident; the danger may spread to the whole area. Proper warning signs ought to be posted so that every person entering understands and acts accordingly.

Signs and symbols are posted in different areas of the lab and on bottles of hazardous chemicals. They indicate that specific precautions must be observed. If you see such signs, be alert and take extra care.

Fig 13.1 (redrawn): warning signs on yellow triangles.

Fig 13.1 (redrawn): mandatory (blue) and prohibition (red) signs.

Shape and colour	Meaning	Examples
Yellow triangle, black border	warning: a hazard is present	flammable, toxic, corrosive, radiation, explosive, asphyxiation, hot surface, biohazard
Blue circle	mandatory: you must do this	wear lab coat, gloves, face mask; wash hands
Red circle with a bar	prohibition: do not do this	no admittance except authorised personnel
Signal word "Danger"	severe hazard	highly flammable, risk of asphyxiation
Signal word "Warning" / "Caution"	less severe hazard; take care	corrosive, general caution

Topic 6

PPE, fire extinguisher and emergencies

Definition

Personal protective equipment (PPE)

Equipment made available to students to face any emergency in the lab and to reduce exposure to hazardous chemicals: lab coat, protective glasses, face shields, apron, boots and hearing protection.

PPE: what to wear and what each item protects.

Lab activity	PPE needed
Any practical	lab coat, safety glasses, closed shoes
Diluting acids, using alkalies	splash goggles, face shield, gloves, apron
Heating, flames	lab coat (cotton), goggles, hair tied back
Toxic or volatile chemicals	fume cupboard, gloves, mask
Noisy machines (grinders, compressors)	hearing protection

Fire extinguisher and emergency shower

Laboratories 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 placed, and a training session should teach them to use it without panic or harm. Similarly an emergency shower must be available, and everyone must know its location and working.

Using an extinguisher: Pull, Aim, Squeeze, Sweep.

Fire of	Use	Never use
Paper, wood, cloth	water, foam, dry powder	—
Flammable liquids (petrol, alcohol)	CO₂, foam, dry powder, fire blanket	water (spreads burning liquid)
Electrical equipment	switch off, then CO₂ or dry powder	water
Reactive metals (Na, K)	dry sand	water, CO₂

Emergency situations

Students should know what to do in an emergency or if a person is affected. Periodic drills should be held with compulsory participation, and students should practise, not just hear lectures. During drills, fire-fighting equipment must be checked.

In an emergency

Stay calm and do not panic.
Alert people in the area to evacuate.
In case of fire, close doors to confine the fire; use the fire extinguisher.
In a chemical emergency, adopt the safety procedures of section 13.1.
Call and assist emergency staff.

Remember

If clothes catch fire: stop, drop and roll, or use the emergency shower / fire blanket. Chemical in the eye: eye wash for at least 15 minutes.

End of Part 1Next: Part 2 · MCQs fully solved ↓

Part 2of 6

MCQs Fully Solved

Try each one first: tap an option to check it, then read the reasoning and why the others are wrong.

Only the mcqs on one page →

A note about the questions

The wording follows published solved exercises and every answer was re-checked by hand, so the wording or the order of options may differ slightly from your print.

Answered 0 of 24 · Correct 0

Set A: Textbook exercise 8 MCQs

The multiple-choice questions at the end of Chapter 13 in your book, in the book's option order.

Q13.1Lab Rules and Conduct

Safety in the chemistry laboratory is:

Q13.2Lab Rules and Conduct

Accidents often result from:

Q13.3Hazard Signs

The label "Warning" on a chemical bottle signifies:

Q13.4Hazard Signs

The label "Corrosive" on a chemical bottle indicates:

Q13.5Corrosive and Toxic Hazards

Example of highly toxic chemical:

Q13.6Reactive, Radiation and Asphyxiation Hazards

Example of self-reactive chemical:

Q13.7Corrosive and Toxic Hazards

When diluting an acid with water:

Q13.8PPE and Emergencies

What should you do in case of a fire drill in the lab.?

Set B: More MCQs from this chapter 16 MCQs

Extra questions on the same ideas, of the kind set in board papers and class tests.

QB1Lab Rules and Conduct

If it is necessary to smell a gas in the laboratory, you should:

QB2Corrosive and Toxic Hazards

A fume cupboard (fume hood) is used for:

QB3Flammable and Explosive Hazards

Flammable chemicals are those which have a flashpoint:

QB4Flammable and Explosive Hazards

Which of these is a flammable compound?

QB5Corrosive and Toxic Hazards

When working with corrosive chemicals one should wear:

QB6Reactive, Radiation and Asphyxiation Hazards

Which of the following is an asphyxiant?

QB7Reactive, Radiation and Asphyxiation Hazards

Exposure to radiation is monitored by wearing:

QB8Corrosive and Toxic Hazards

Acid and alkali waste is disposed of by:

QB9Flammable and Explosive Hazards

Which of these is an explosive chemical named in the book?

QB10Corrosive and Toxic Hazards

Which of these is a toxic chemical?

QB11Hazard Signs

A hazard sign showing a skull and crossbones means:

QB12Hazard Signs

A hazard sign showing liquid dripping from test tubes onto a hand and a surface means:

QB13PPE and Emergencies

A fire caused by an electrical short circuit should be put out with:

QB14Reactive, Radiation and Asphyxiation Hazards

Sodium metal is stored:

QB15PPE and Emergencies

Which item of PPE protects the eyes from chemical splashes?

QB16PPE and Emergencies

In an emergency in the laboratory, the first thing to do is:

End of Part 2Next: Part 3 · Short questions ↓

Part 3of 6

Short Questions

Exam-ready answers. Learn the meaning, then write them in your own words.

Only the short questions on one page →

Set A: Textbook exercise short questions 8 questions

The short questions at the end of the chapter in your book.

Short Q 13.1

Name some corrosive chemicals.

Answer

Mineral acids including HF (also concentrated H₂SO₄, HCl, HNO₃), caustic alkalies (NaOH, KOH) and glacial acetic acid. They attack skin, eyes and the respiratory tract.

Short Q 13.2

What type of safety precautions are adopted to avoid damage due to explosive chemicals?

Answer

Do not move a container suspected to explode (avoid shock).
Obtain prior approval from the teacher; use the smallest quantity.
Work in a fume hood behind a shield; remove other chemicals and apparatus.
Inform others; wear safety spectacles, gloves and a lab coat.
Keep away from heat; dispose of the waste properly.

Short Q 13.3

What type of damages can reactive chemicals cause?

Answer

When reactions are not properly performed, reactive chemicals may cause fires and explosions, and may evolve dangerous gases. These can cause extreme damage to life and property: burns, injuries from flying glass, poisoning, damage to the lab.

Short Q 13.4

Indicate two safety instructions which are required to avoid radiation.

Answer

Keep radioactive sources shielded and avoid prolonged exposure.
Monitor exposure with badges and wear protective clothing; avoid contact with bare skin.

Short Q 13.5

Which chemicals can cause suffocation?

Answer

Asphyxiants: hydrogen cyanide, carbon monoxide, nitrogen, argon, helium, methane and carbon dioxide. N₂, Ar, He, CH₄ and CO₂ push out oxygen; CO and HCN stop the body using oxygen.

Short Q 13.6

Why are signs and symbols posted in the lab and on chemical bottles?

Answer

To let people know the hazardous nature of the area or chemical, so that every person entering understands and acts accordingly; they indicate that specific precautions must be observed. Symbols are understood at a glance, even without reading.

Short Q 13.7

How should a fire caused by chemicals be handled?

Answer

Stay calm; alert others and evacuate those near.
Turn off gas and electricity; remove other flammables if safe.
Smother a small fire in a beaker with a lid or fire blanket.
Use the right extinguisher: CO₂ or dry powder for flammable liquids, dry sand for sodium/potassium; never water on burning oil or reactive metals.
If it spreads, close doors to confine it, leave and call the fire brigade.

Short Q 13.8

Why are emergency drills important to face emergency situations?

Answer

Drills let students practise the actions to take in an emergency, not just hear about them. In a real emergency people act from practice: they stay calm, know the exits, the extinguisher and shower locations, and leave in order. During drills, fire-fighting and other equipment is also checked to be in working order.

Set B: More short questions 34 questions

The book's in-text exercises first, then short questions on every topic of the chapter (SLO-based), as asked in board papers.

Practice exercise questions (in text)

SQ 13.1

Why are flammable liquids not stored in a refrigerator?

Answer

An ordinary refrigerator has sparks inside (thermostat switch, light switch, motor). Vapours of flammable liquids collect in the closed cabinet and can be ignited by a spark, causing an explosion. Only special spark-proof (laboratory-safe) refrigerators may be used.

SQ 13.2

Can you wear contact lenses in the lab?

Answer

It is best not to. Vapours and splashes can get trapped behind a lens and damage the eye, and lenses are hard to remove quickly to rinse the eye. If they must be worn, always wear sealed safety goggles over them and tell the teacher.

SQ 13.3

Under which circumstances are explosive chemicals likely to explode?

Answer

On sudden shock, friction or impact (dropping, moving the container), on heating or near flames and sparks, and when some of them dry out (picric acid is far more dangerous when dry) or grow old (peroxides).

SQ 13.4

How will you dispose of acid and alkali waste after the experiment is finished?

Answer

Acids and bases are first neutralised, then flushed to the sewer with plenty of water. Hazardous waste is sent to a hazardous waste disposal site, never poured straight down the drain.

SQ 13.5

What message does the warning sign "Caution" convey?

Answer

Take care: there is a possible hazard here which could cause minor or moderate injury if you are careless. It is a lower level than "Danger".

SQ 13.6

Name some explosive chemicals.

Answer

Picric acid, 2,4-dinitrophenylhydrazine, benzoyl peroxide and nitrocellulose.

SQ 13.7

Should emergency drills be compulsory or optional?

Answer

Compulsory. The book says periodic drills should be held with compulsory participation. An emergency affects everyone, and one untrained person can block exits or panic others.

Lab rules and waste

SQ 13.8

What is a chemistry laboratory?

Answer

A place where a student is trained to observe the physical and chemical characteristics of substances by following definite procedures.

SQ 13.9

Why should students not work alone in the lab?

Answer

If an accident happens, no one would be there to help or call for help. Experiments should be done in the presence of the instructor and lab staff.

SQ 13.10

Why is food not allowed in the lab?

Answer

Food can pick up traces of toxic or corrosive chemicals from benches and hands and be swallowed.

SQ 13.11

How should a gas be smelled in the lab?

Answer

Never smell directly. Waft the fumes or vapours towards your nose with your hand, from a distance.

Wafting.

SQ 13.12

Name chemicals that can create safety problems in a lab.

Answer

Cleaning agents, disinfectants, solvents, paints, compressed gas cylinders, mineral acids and carcinogenic chemicals.

SQ 13.13

How is non-hazardous and hazardous lab waste disposed of?

Answer

Non-hazardous waste: sewer or trash bin. Acids and bases: neutralised, then sewer. Hazardous waste: transported to a hazardous waste disposal site.

Chemical hazards

SQ 13.14

What are flammable chemicals? Give examples.

Answer

Chemicals or mixtures which have a flashpoint around room temperature: ethers, methylated spirit, benzene, acetone, petrol.

SQ 13.15

What are explosive chemicals?

Answer

Chemicals that cause a sudden release of pressure, gas and heat when they experience a sudden shock.

SQ 13.16

What are corrosive chemicals?

Answer

Chemicals that attack living tissues when they come in contact with them; solids, liquids or gases that attack skin, eyes, respiratory tract and intestine.

SQ 13.17

Why should acid be added to water and not water to acid?

Answer

Dilution gives out a lot of heat. Water added to concentrated acid boils at once and spatters hot acid; acid added slowly to water is diluted immediately and the heat spreads safely.

Acid into water.

SQ 13.18

What is a toxic chemical? Give examples.

Answer

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

SQ 13.19

Why should toxic chemicals be kept in their original containers?

Answer

The original container carries the correct name and hazard label, and is made of a material that suits the chemical; transferring it risks spills and mix-ups.

SQ 13.20

Give examples of reactive chemicals.

Answer

Calcium hydride, sodium, lithium, azides, picric acid, AlCl₃, benzoyl peroxide.

SQ 13.21

Why is glass equipment wrapped with tape when using reactive chemicals?

Answer

If the reaction becomes violent and the glass breaks, the tape holds the pieces so that flying glass does not injure anyone.

SQ 13.22

What are the effects of a high dose of radiation?

Answer

Damage to tissues and organs, vomiting, radiation burns, hair loss and radiation syndrome.

SQ 13.23

Which radiations are most harmful inside and outside the body?

Answer

Alpha and beta emitters do extreme damage when inhaled or injected; gamma rays cause external injuries because they pass through the body.

SQ 13.24

What is an asphyxiation hazard?

Answer

A hazard in which a gas or vapour can cause unconsciousness or death through suffocation. The victim gets no warning of low oxygen.

SQ 13.25

What are the symptoms of low oxygen?

Answer

Rapid breathing, rapid heart rate, nausea and convulsions, then unconsciousness.

Hazard signs

SQ 13.26

What does a yellow triangle with a black border mean?

Answer

A warning sign: a hazard is present (the picture inside shows which: flame, skull, trefoil, corroding hand...).

Warning signs.

SQ 13.27

What is the difference between "Danger" and "Warning" on a label?

Answer

"Danger" marks the more severe hazards (e.g. highly flammable, risk of asphyxiation); "Warning" marks less severe hazards (e.g. corrosive to skin, harmful).

SQ 13.28

What do blue circular signs mean?

Answer

Mandatory signs: you must do what they show, e.g. lab coats must be worn, wear face mask, wear gloves, sanitise hands here.

Mandatory and prohibition signs.

SQ 13.29

What does a red circle with a diagonal bar mean?

Answer

A prohibition: do not do this, e.g. "No admittance, authorised personnel only".

PPE and emergencies

SQ 13.30

What is PPE? Name some items.

Answer

Personal protective equipment, made available to students to face emergencies and reduce exposure to hazardous chemicals: lab coat, protective glasses, face shields, apron, boots and hearing protection.

SQ 13.31

Why should students know the location of the fire extinguisher?

Answer

So that a small fire can be controlled quickly before it spreads; in an emergency there is no time to search.

SQ 13.32

What is an emergency shower used for?

Answer

To wash off a large chemical splash on the body or to put out burning clothes.

SQ 13.33

Write the steps of using a fire extinguisher.

Answer

PASS: Pull the pin, Aim at the base of the fire, Squeeze the handle, Sweep from side to side.

PASS.

SQ 13.34

Write the five steps to cope with an emergency in the lab.

Answer

Stay calm and do not panic.
Alert people to evacuate.
In a fire, close doors and use the extinguisher.
In a chemical emergency, follow the safety procedures.
Call and assist emergency staff.

End of Part 3Next: Part 4 · Constructed response ↓

Part 4of 6

Constructed Response Questions

These test whether you really understand. Give a reason every time.

CRQ 13.1

How will you handle an emergency situation caused by fire due to short circuiting?

Answer

Stay calm and alert everyone to move away from the fire.
Switch off the main electric supply first (the mains switch or circuit breaker).
Never use water: it conducts electricity and can electrocute you.
Use a CO₂ or dry powder extinguisher, using PASS: pull, aim at the base, squeeze, sweep.
Turn off the gas supply and move flammable chemicals away if safe.
If the fire spreads, close the doors to confine it, evacuate and call the fire brigade (1122 in Punjab).

Using an extinguisher.

CRQ 13.2

What type of reactions should be carried out in a fume cupboard?

Answer

Reactions that give toxic gases: H₂S, Cl₂, NO₂, SO₂, HCN, NH₃.
Work with corrosive chemicals that give corrosive vapours (concentrated HCl, HNO₃).
Work with volatile flammable or toxic solvents (ether, benzene, chloroform).
Reactions with explosive or reactive chemicals, behind the sash as a shield.

The fan of the fume cupboard draws the vapours away from the worker and out of the building.

CRQ 13.3

Put forward at least two suggestions to improve safety in the lab.

Answer

Compulsory PPE: no student starts work without lab coat and goggles; goggles kept at every bench.
Regular, compulsory drills and training in using the extinguisher, shower and eye wash.
Clear hazard signs and labels on every area and bottle; a chart of signs on the wall.
Safe storage: flammables in a fire-proof cabinet, acids apart from bases, reactive metals under oil.
Smaller quantities and safer alternatives; working fume cupboards and good ventilation.

CRQ 13.4

Can you identify the warning symbols posted for radiation and asphyxiant chemicals?

Answer

Radiation: a black trefoil (a small circle with three blades around it) on a yellow triangle or square, usually labelled "Radiation hazard".

Asphyxiation: a yellow triangle with a person collapsing/kneeling, holding the throat, with "Danger: risk of asphyxiation".

Radiation and asphyxiation signs among the warning signs.

CRQ 13.5

Why can a sudden shock cause some chemicals to explode?

Answer

Explosive chemicals such as picric acid, benzoyl peroxide and nitrocellulose are unstable: their molecules contain weak bonds and plenty of oxygen-rich groups (–NO₂, –O–O–) close to fuel atoms (C, H).

A sudden shock or friction gives a small spot enough energy to break a few weak bonds. The decomposition is highly exothermic, so the heat breaks neighbouring molecules, and the reaction spreads through the whole sample in a fraction of a second.

Large volumes of hot gas (CO₂, N₂, H₂O) are formed almost instantly from a solid, so pressure, gas and heat are released suddenly: an explosion.

End of Part 4Next: Part 5 · Comprehensive questions ↓

Part 5of 6

Comprehensive (Long) Questions

Long answers, explained in full with headings. Learn the structure: definition, explanation, diagram or table, example.

Only the long questions on one page →

Set A: Textbook comprehensive questions 6 questions

The long questions at the end of the chapter in your book.

Long Q 13.1

Explain the hazards due to explosive and toxic chemicals.

Answer

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.

Explosive and toxic warning signs.

Long Q 13.2

Write down five common safety instructions which are used to avoid all types of hazards.

Answer

Never work alone; work in the presence of the teacher and follow the instructions exactly.
Always wear PPE: lab coat, safety goggles, gloves and closed shoes.
Use the smallest quantity of any chemical, and use a fume cupboard for anything that gives vapours.
Read the label and hazard sign before using a chemical; keep chemicals in labelled original containers.
Never taste or smell chemicals directly; no food or drink in the lab; wash hands after work.
Dispose of waste properly: neutralise acids and bases; hazardous waste to the proper site; never down the drain.
Know the emergency equipment: fire extinguisher, shower, eye wash, exits.

Long Q 13.3

Explain the importance of warning signs and symbols to avoid any accident in the lab.

Answer

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

Instant message: a picture is understood at a glance by anyone, even a visitor, without reading.
Tell the precaution: each sign shows what to do (wear goggles) or what not to do (no entry).
Mark the level of danger: "Danger" for severe hazards, "Warning" or "Caution" for less severe.
Locate equipment: signs show exits, extinguishers, showers and eye wash.
Help in emergencies: fire-fighters know which chemicals are inside.

Warning signs.

Mandatory and prohibition signs.

Long Q 13.4

Name some toxic chemicals. Describe the effects of a toxic gas spreading in the lab.

Answer

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

Eyes, nose and throat sting and water (chlorine, ammonia).
Coughing, choking, difficulty in breathing; lung damage and fluid in the lungs at higher doses.
Headache, dizziness, nausea; with CO or HCN, the body cannot use oxygen, leading to unconsciousness and death.
The gas spreads to the whole building and nearby people; panic may cause more injuries.
Some gases are colourless and odourless (CO), so people do not notice them.

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.

Long Q 13.5

A student has spilled a corrosive and explosive chemical due to an accident. Which emergency measures will you take to tackle the situation?

Answer

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.

Long Q 13.6

(Investigative) A few decades ago, a tanker carrying poisonous chlorine gas leaked and the gas spread over a large area in Lahore. The accident killed a few persons as well as animals. Give some concrete proposals to avoid such an accident in future.

Answer

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

Tankers must be tested and certified regularly; valves and pressure gauges checked before every trip.
Drivers specially trained in hazardous materials and emergency action.
Clear hazard signs (toxic gas, UN number) on the tanker so rescuers know what it carries.

During transport

Use fixed routes away from crowded areas; travel at night or off-peak; speed limits and escort vehicles.
GPS tracking and leak sensors that alert the authorities.

If a leak happens

Rescue 1122 and fire brigade trained and equipped (gas masks, protective suits); water sprays can knock down chlorine gas.
Warn people to move upwind and to higher ground (chlorine sinks), stay indoors with windows closed, cover the nose with a wet cloth.
Hospitals near routes prepared to treat chlorine poisoning.

Policy

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

Set B: More important long questions 5 questions

Long questions often set in board papers from this chapter, answered in the same full style.

Imp. LQ 1

Describe the general rules for working safely in a chemistry laboratory.

Answer

Before work

Get familiar with the layout of the laboratory and the fittings on tables and shelves; know where exits, extinguisher, shower and eye wash are.
Check equipment before use and work out the potential hazards of the experiment.

Know the lab layout.

During work

Behave responsibly; do not work alone; work in the presence of the instructor.
No crowding; keep to your place at a safe distance from others.
No food items in the lab.
Never taste or smell any compound or gas; waft the vapours if smelling is necessary.
Wear PPE: lab coat, goggles, gloves.

After work

Do not pour chemicals down the drain. Neutralise acids and bases before sewer disposal; send hazardous waste to the disposal site.
Keep sinks and drains clean; wash your hands.

Appropriate safety precautions must be observed at all cost.

Imp. LQ 2

Describe corrosive hazards and the precautions to be taken while handling corrosive chemicals.

Answer

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

Wear splash goggles instead of safety glasses, and a face shield.
Use corrosive chemicals in a fume cupboard.
Add acid slowly to water, never water to acid.
Ensure an eye wash and emergency shower are available.
Wash an affected area with soap and water; seek medical attention.

Acid into water.

The corrosive sign among the warning signs.

Imp. LQ 3

Describe reactive, radiation and asphyxiation hazards with their safety instructions.

Answer

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.

Radiation and asphyxiation signs.

Imp. LQ 4

What is personal protective equipment? Describe the PPE needed for different laboratory activities.

Answer

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.

PPE items.

What each item protects

Item	Protects
Lab coat / apron	skin and clothes from splashes and flames
Safety glasses / splash goggles	eyes
Face shield	whole face (corrosives, reactive chemicals)
Gloves	hands from corrosive, toxic and hot materials
Boots / closed shoes	feet from spills and broken glass
Mask	lungs from dust and vapour
Hearing protection	ears from loud machines

Choosing PPE

Activity	PPE
Any practical	lab coat, glasses, closed shoes
Diluting acids	splash goggles, face shield, gloves, apron
Toxic vapours	fume cupboard, mask, gloves
Radioactive sources	protective clothing, gloves, badge

Imp. LQ 5

Why must students know the location of the fire extinguisher and emergency shower? How should an emergency be handled?

Answer

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.

PASS: Pull, Aim, Squeeze, Sweep.

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.

Locate the nearest extinguisher and shower.

Handling an emergency

Stay calm and do not panic.
Alert people in the area to evacuate.
In case of fire, close doors to confine it; use the extinguisher.
In a chemical emergency, follow the safety procedures for that hazard.
Call and assist emergency staff.

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

End of Part 5Next: Part 6 · Revision & self-test ↓

Part 6of 6

Revision, Practice and Self-Test

Use this the night before the test.

One-page key facts

Flammable

flashpoint near room temperature: ether, acetone, petrol, benzene

Explosive

sudden pressure, gas, heat on shock: picric acid, benzoyl peroxide

Corrosive

attacks living tissue: HF and mineral acids, caustic alkalies

Toxic

poisonous: Hg, benzene, Cl₂, NH₃, HCN, pesticides

Reactive

CaH₂, Na, Li, azides, AlCl₃

Asphyxiants

HCN, CO, N₂, Ar, He, CH₄, CO₂

Diluting acid

add acid to water, slowly, stirring

Smelling

waft, never sniff; never taste

Acid/base waste

neutralise, then sewer

Signal words

Danger = severe; Warning / Caution = less severe

Extinguisher

PASS: Pull, Aim, Squeeze, Sweep

Electrical fire

switch off; CO₂ or dry powder, never water

Key definitions 7 terms

Explosive chemicals

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

Flammable chemicals

Chemicals or mixtures which have a flashpoint around room temperature. Examples: ethers, methylated spirit, benzene, acetone, petrol.

Flashpoint

The lowest temperature at which a liquid gives enough vapour to catch fire from a flame or spark.

Corrosive chemicals

Chemicals that 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.

Toxic chemical

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

Asphyxiation hazard

A hazard in which a gas or vapour can cause unconsciousness or death through suffocation.

Personal protective equipment (PPE)

Equipment made available to students to face any emergency in the lab and to reduce exposure to hazardous chemicals: lab coat, protective glasses, face shields, apron, boots and hearing protection.

Common mistakes to avoid

Adding water to acid.
Sniffing a gas directly instead of wafting.
Storing flammable liquids in an ordinary refrigerator.
Using water on an electrical, oil or sodium fire.
Wearing ordinary glasses instead of splash goggles with corrosives.
Moving a container suspected to explode.
Pouring acids or bases straight down the drain.
Running or carrying chemicals during a fire drill.

Extra practice tap a question to see its answer

Whose responsibility is lab safety?Show answer
Shared by everyone
What does "Warning" on a bottle mean?Show answer
Less serious injury possible
What does "Corrosive" mean?Show answer
Destroys living tissue on contact
Highly toxic: ethanol or potassium cyanide?Show answer
Potassium cyanide
Self-reactive chemical?Show answer
Picric acid
Acid to water or water to acid?Show answer
Acid to water
First action in a fire drill?Show answer
Close gas valves, switch off equipment
How to smell a gas?Show answer
Waft it towards the nose
Sign with skull and crossbones?Show answer
Toxic
Where is sodium stored?Show answer
Under kerosene oil
How is radiation exposure monitored?Show answer
With badges
Blue circular signs mean?Show answer
Mandatory: you must do this

Final self-test

Final self-test: all 24 MCQs, no answers

Give yourself 25 minutes. Pick one option for each question, then submit to see your score and which questions to revise. Any question you get wrong tells you which topic to read again.

End of Part 6Back to Part 1 ↑