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VCE Vet Laboratory Skills study materials
VCE Vet Laboratory Skills study resources

VCE Vet Laboratory Skills practice questions

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Question 1Workplace safety and occupational health procedures in the laboratory

In a school laboratory, which document should a student consult first to find the correct handling precautions for a chemical before using it?

  1. The laboratory's equipment inventory
  2. The class timetable for the week
  3. The previous year's examination paper
  4. The chemical's safety data sheet Correct answer.

Explanation

A safety data sheet is the standard source of information on a chemical's hazards, safe handling, storage, spill response and first aid. Students should read it before using an unfamiliar substance so that controls are in place beforehand. Timetables, inventories and past papers contain no hazard information.

Question 2Workplace safety and occupational health procedures in the laboratory

Which item of personal protective equipment is required whenever there is a risk of splashes to the eyes in the laboratory?

  1. A hair tie or hair net
  2. Safety spectacles or goggles Correct answer.
  3. A laboratory coat only
  4. Closed-toe shoes only

Explanation

Eye protection such as safety spectacles or goggles is the control that guards against chemical splashes, flying particles and biological aerosols reaching the eyes. A coat, shoes and hair ties protect other parts of the body or control contamination but leave the eyes exposed. Eye protection should be worn whenever the risk assessment identifies a splash hazard.

Question 3Workplace safety and occupational health procedures in the laboratory

A student notices a small chemical spill on the bench during a practical class. What is the most appropriate first action?

  1. Stop work and alert the teacher or supervisor Correct answer.
  2. Wipe the spill up with a paper towel and continue
  3. Leave the room without telling anyone
  4. Dilute the spill with water and keep working

Explanation

The first step in any spill is to stop work, warn people nearby and notify the supervisor so the hazard can be assessed and the correct clean-up procedure chosen. Cleaning up without advice risks exposure to an unknown substance or an incompatible reaction. Leaving silently means others remain at risk.

Question 4Workplace safety and occupational health procedures in the laboratory

Which practice best reduces the risk of inhaling chemical vapours while working at a laboratory bench?

  1. Opening nearby windows and closing the fume cupboard
  2. Pointing the container towards your face to see inside
  3. Carrying out the procedure in a fume cupboard Correct answer.
  4. Working quickly so vapours do not build up

Explanation

A fume cupboard captures and removes vapours, gases and aerosols at the point where they are generated, preventing them entering the breathing zone. Working faster does not reduce the amount of vapour released. Looking into a container and relying on windows alone do not provide reliable local exhaust ventilation.

Question 5Workplace safety and occupational health procedures in the laboratory

Why is eating and drinking prohibited in a laboratory?

  1. It makes the benches dirty and harder to clean
  2. It uses up time that should be spent on practicals
  3. It distracts other students from their work
  4. Food can become contaminated with hazardous substances Correct answer.

Explanation

Hazardous chemicals and microorganisms can settle on food, hands and surfaces, so eating or drinking in the laboratory creates a route of ingestion exposure. The rule protects health rather than tidiness or time. Distraction and mess are secondary concerns, not the reason for the prohibition.

Question 6Workplace safety and occupational health procedures in the laboratory

What is the correct way to smell a chemical in the laboratory when the procedure requires it?

  1. Heat the container first, then sniff the opening
  2. Waft the vapour gently towards your nose Correct answer.
  3. Inhale deeply with your face close to the opening
  4. Place your nose directly over the container

Explanation

Wafting moves a small, diluted amount of vapour towards the nose so that an odour can be detected without a large exposure. Putting the face close to the container, inhaling deeply or heating the substance can deliver a concentrated dose and cause harm. Wafting is the standard technique taught for odour detection.

Question 7Workplace safety and occupational health procedures in the laboratory

Which of the following is a correct procedure for washing hands after a laboratory session?

  1. Wash with soap and water and dry with a clean towel Correct answer.
  2. Wipe hands on the laboratory coat
  3. Rinse briefly with cold water only
  4. Use a solvent such as ethanol to remove residues

Explanation

Thorough handwashing with soap and water removes chemical residues and microorganisms from the skin, and drying with a clean towel prevents recontamination. A brief cold rinse is not effective at removing many substances. Solvents damage skin and can increase absorption, and clothing transfers contamination.

Question 8Workplace safety and occupational health procedures in the laboratory

A beaker of hot liquid is being carried across the laboratory. Which action best reduces the risk of a burn?

  1. Carry it with both hands and warn others nearby Correct answer.
  2. Carry it quickly to shorten the exposure time
  3. Hold the beaker by the rim with the fingers
  4. Fill the beaker to the brim so it is not carried twice

Explanation

Using both hands gives a secure grip and warning others lets them move clear, reducing the chance of a collision and spill of hot liquid. Moving quickly increases the risk of tripping, overfilling makes spills likely, and holding the rim puts fingers close to the hot content.

Question 9Workplace safety and occupational health procedures in the laboratory

What does a hazard pictogram showing a flame indicate about a chemical?

  1. It is flammable and can ignite readily Correct answer.
  2. It is an oxidising agent that releases oxygen
  3. It is corrosive to skin and metals
  4. It is toxic if inhaled or swallowed

Explanation

The flame pictogram marks flammable substances, which can ignite when exposed to a spark, flame or heat source. Corrosive and toxic hazards use different pictograms. The oxidising pictogram shows a flame over a circle, which is distinct from the plain flame symbol.

Question 10Workplace safety and occupational health procedures in the laboratory

A student with long hair is about to use a Bunsen burner. Which control is most directly aimed at preventing the hair from catching fire?

  1. Light the burner before tying the hair back
  2. Stand further from the bench while the burner is lit
  3. Tie the hair back securely before lighting the burner Correct answer.
  4. Wear a laboratory coat over the hair

Explanation

Tying long hair back keeps it away from the flame, which is the direct control for the ignition hazard. Moving away from the bench reduces the ability to work safely and does not secure the hair. A coat does not cover the head, and lighting first creates the hazard before the control is applied.

Question 11Workplace safety and occupational health procedures in the laboratory

Which statement correctly describes the purpose of a risk assessment before a practical activity?

  1. It provides a timetable for completing each step
  2. It records accidents that have already occurred
  3. It lists the chemicals that the school has in stock
  4. It identifies hazards and records controls before work begins Correct answer.

Explanation

A risk assessment is completed before work starts and identifies hazards, who may be harmed, the likelihood and severity of harm, and the controls that will reduce the risk. Accident records and chemical inventories are separate documents. A schedule of steps is a procedure, not a risk assessment.

Question 12Workplace safety and occupational health procedures in the laboratory

A glass bottle of reagent has cracked and liquid is leaking onto the shelf. What is the safest sequence of actions?

  1. Pick up the bottle with bare hands and move it to the sink
  2. Warn others, tell the supervisor, then follow the spill procedure Correct answer.
  3. Rinse the shelf with water and return the bottle to storage
  4. Add absorbent material immediately and place the bottle in a bin

Explanation

Warning others and informing the supervisor ensures the hazard is assessed and the correct spill procedure and protective equipment are used. Handling a leaking bottle with bare hands or improvising clean-up risks exposure and injury. Rinsing with water may spread the substance or cause a reaction.

Question 13Workplace safety and occupational health procedures in the laboratory

Which action is appropriate when a chemical splashes into a student's eye?

  1. Rub the eye with a tissue to remove the chemical
  2. Close the eye tightly until the stinging stops
  3. Flush the eye with water at the eyewash station and seek help Correct answer.
  4. Apply eye drops from the first aid kit and continue

Explanation

Immediate and prolonged flushing with clean water at an eyewash station dilutes and removes the chemical, and help is then sought for further treatment. Rubbing the eye can cause abrasion and spread the substance. Eye drops are not a substitute for flushing, and keeping the eye closed traps the chemical against the tissue.

Question 14Workplace safety and occupational health procedures in the laboratory

Why should broken glass be swept up with a dustpan and brush rather than picked up by hand?

  1. Sweeping is the only method allowed by law
  2. Glass fragments damage the broom bristles
  3. Sharp fragments can cut skin and cause infection Correct answer.
  4. Glass is too heavy to lift by hand safely

Explanation

Using a dustpan and brush keeps hands away from sharp edges, reducing the risk of cuts and possible infection or contamination of the wound. The concern is injury to the person, not damage to equipment. Weight and legal restriction are not the reasons for this practice.

Question 15Workplace safety and occupational health procedures in the laboratory

A student needs to move a large winchester of concentrated acid from a low shelf to the bench. Which approach best reduces the risk of injury?

  1. Carry it against the chest with both arms
  2. Lift it quickly by the neck to reduce handling time
  3. Roll the bottle along the bench edge to the work area
  4. Use a bottle carrier and ask for help if it is heavy Correct answer.

Explanation

A bottle carrier gives a secure grip and contains any leakage, and asking for help prevents strain and dropping when the container is heavy. Carrying against the chest risks spills onto the body. Rolling the bottle and lifting by the neck give poor control and can cause breakage or spillage.

Question 16Workplace safety and occupational health procedures in the laboratory

Which of the following correctly describes how compressed gas cylinders should be secured in the laboratory?

  1. Stored loose in a cupboard with the valve open
  2. Laid horizontally on the floor beneath the bench
  3. Upright and fastened with a chain or strap to a fixed support Correct answer.
  4. Leaned against a wall without restraint

Explanation

Cylinders should stand upright and be restrained by a chain or strap so they cannot fall and damage the valve, which could release gas rapidly. Laying them down, leaving them unrestrained or storing with the valve open all create serious uncontrolled-release hazards. Securing the cylinder is a basic control for stored pressure energy.

Question 17Workplace safety and occupational health procedures in the laboratory

A student is using a centrifuge and notices it begins to vibrate strongly. What is the safest response?

  1. Hold the lid down firmly until the run finishes
  2. Open the lid immediately to inspect the tubes
  3. Increase the speed so the vibration settles
  4. Stop the centrifuge, wait for it to stop, then check the load Correct answer.

Explanation

Strong vibration usually means the tubes are unbalanced or a tube has broken, so the run should be stopped and the rotor allowed to come to rest before the load is checked. Holding the lid or increasing speed does not correct the imbalance and may worsen it. Opening the lid while the rotor spins exposes the user to flying fragments and aerosols.

Question 18Workplace safety and occupational health procedures in the laboratory

Which statement about the storage of chemicals in a school laboratory is correct?

  1. All chemicals are stored together alphabetically for easy finding
  2. Acids are stored above bases so they are easy to reach
  3. Incompatible substances are kept apart according to their hazard class Correct answer.
  4. Flammable liquids are stored next to ignition sources for convenience

Explanation

Chemicals must be segregated by hazard class so that incompatible substances cannot mix and react if a container leaks or breaks. Alphabetical storage ignores compatibility and can place reactive pairs together. Storing acids above bases and flammables near ignition sources creates avoidable serious hazards.

Question 19Workplace safety and occupational health procedures in the laboratory

A small fire starts in a waste bin in the laboratory. Which action should be taken first?

  1. Wait to see whether the fire goes out by itself
  2. Fan the flames to direct them away from equipment
  3. Raise the alarm and follow the emergency procedure Correct answer.
  4. Throw water on the fire immediately

Explanation

Raising the alarm and following the emergency procedure ensures people are warned and the correct extinguishing method and evacuation are used. Water is unsuitable for many laboratory fires, including some chemical and electrical fires. Fanning supplies oxygen and waiting allows the fire to grow.

Question 20Workplace safety and occupational health procedures in the laboratory

A student is asked to dilute concentrated sulfuric acid. Which procedure is correct?

  1. Add the acid slowly to water with stirring Correct answer.
  2. Mix the acid and water together quickly in a beaker
  3. Heat the acid first, then add water
  4. Add water slowly to the concentrated acid

Explanation

Diluting concentrated acid releases a large amount of heat, so the acid is added slowly to water with stirring and cooling so the heat is absorbed by the larger volume of water. Adding water to concentrated acid can cause violent boiling and spitting. Mixing quickly or heating increases the risk further.

Question 21Workplace safety and occupational health procedures in the laboratory

A student develops a rash on the forearms after a practical class. Which action best reflects correct incident reporting?

  1. Ask a classmate to write a note in their own workbook
  2. Ignore it because skin reactions are not serious
  3. Report the reaction to the teacher and record it in the incident log Correct answer.
  4. Wait until the end of the term to mention it

Explanation

Any adverse health effect arising from laboratory work should be reported promptly to the supervisor and recorded so that the cause can be investigated and controls improved. Ignoring or delaying the report allows the hazard to remain and prevents proper documentation. A classmate's workbook is not an official record.

Question 22Workplace safety and occupational health procedures in the laboratory

A laboratory has a spill kit containing absorbent, a dustpan, gloves and a waste bag. Why should the kit be checked regularly?

  1. The absorbent becomes more effective with age
  2. Materials may be missing or expired when an emergency occurs Correct answer.
  3. Checking the kit is required to keep the cupboard tidy
  4. Regular checks reduce the number of spills that happen

Explanation

Spill kits are only useful if all items are present and in date when needed, so periodic checks ensure the equipment will work during an emergency. Tidiness is not the reason for inspection. Absorbents do not improve with age, and checking a kit cannot prevent spills from occurring.

Question 23Workplace safety and occupational health procedures in the laboratory

In a laboratory, a worker is exposed to a chemical that has a workplace exposure standard. What does this standard represent?

  1. The dose that is always fatal to humans
  2. The temperature at which the chemical becomes dangerous
  3. A concentration in air that should not be exceeded over a stated period Correct answer.
  4. The maximum volume of the chemical that may be stored

Explanation

An exposure standard sets an airborne concentration that should not be exceeded, usually expressed over a reference period such as an eight-hour shift or a short-term peak. It guides monitoring and ventilation design. It does not specify storage volumes, ignition temperatures or a universally fatal dose.

Question 24Workplace safety and occupational health procedures in the laboratory

A student argues that because a chemical is labelled 'low hazard' on its container, no risk assessment is needed. Which response is most accurate?

  1. The label guarantees the substance cannot cause harm
  2. Low-hazard substances are exempt from all laboratory rules
  3. Risk assessment is only needed for chemicals stored in large volumes
  4. Risk depends on how the substance is used, so assessment is still required Correct answer.

Explanation

Hazard is an intrinsic property of a substance, while risk depends on the amount used, the route of exposure, the equipment and the controls in place. Even a low-hazard substance can cause harm if heated, inhaled as a dust or used in large quantities. The law requires assessment of the activity, not just the label classification.

Question 25Workplace safety and occupational health procedures in the laboratory

Two chemicals are stored in the same cupboard because each is individually safe. What is the main reason this practice may still be unsafe?

  1. Storing them together uses more shelf space
  2. The labels will fade faster when close together
  3. A leak could allow the chemicals to mix and react Correct answer.
  4. The cupboard will become too heavy to open

Explanation

Segregation is based on compatibility between substances, not only on the hazard of each one alone. If containers leak, incompatible chemicals can mix and produce heat, toxic gas or fire. Weight, label fading and space are not the safety reasons for segregating chemicals.

Question 26Workplace safety and occupational health procedures in the laboratory

A student notices a chemical container in the laboratory has lost its label, so the contents cannot be identified. What is the correct action?

  1. Label it with the name of the nearest similar bottle
  2. Smell it carefully to identify the chemical
  3. Report it to the teacher and do not use it Correct answer.
  4. Leave it in place and continue the practical

Explanation

An unlabelled container cannot be safely handled because the hazards of its contents are unknown, so it must be reported to the supervisor rather than used. Only a person with the right knowledge should identify and relabel or dispose of it. Guessing the identity puts everyone nearby at risk.

Question 27Workplace safety and occupational health procedures in the laboratory

Which piece of personal protective equipment protects the eyes from chemical splashes during a practical activity?

  1. A laboratory coat
  2. Safety glasses with side shields Correct answer.
  3. Nitrile gloves
  4. Closed-toe shoes

Explanation

Eye protection such as safety glasses or goggles forms a barrier over the eyes and is the specified control for splash hazards. A laboratory coat, closed shoes and gloves protect the body, feet and hands but leave the eyes exposed. Each item of protective equipment is chosen to match the route of exposure it controls.

Question 28Workplace safety and occupational health procedures in the laboratory

A laboratory worker must decant a volatile solvent at the fume cupboard. Which control most directly reduces inhalation exposure during this task?

  1. Keeping the solvent container capped between pours
  2. Wearing a laboratory coat buttoned to the neck
  3. Working with the sash lowered to the marked height Correct answer.
  4. Placing a spill tray beneath the container

Explanation

A fume cupboard captures and removes airborne vapours only when air is drawn in across the working opening, so the sash is kept at or below the marked position during use. Lowering the sash increases the face velocity at the opening and keeps vapours inside the enclosure. The other measures address contamination or spills rather than airborne exposure.

Question 29Workplace safety and occupational health procedures in the laboratory

During a practical, a student receives a small cut from a broken glass slide. Which sequence of actions best follows correct incident procedure?

  1. Stop work, report the injury, and let the teacher manage first aid and recording Correct answer.
  2. Clean the cut, return to the task, and mention it at the end of the lesson
  3. Apply a dressing first, then report the injury to the teacher
  4. Wash the cut, apply a dressing, then continue without telling anyone

Explanation

Every injury in a school laboratory must be reported so that first aid can be given and the incident recorded as required by workplace safety procedures. The teacher supervises the response, arranges appropriate treatment and completes the documentation. Continuing work before reporting delays care and loses the details needed for the incident record.

Question 30Workplace safety and occupational health procedures in the laboratory

A teacher is deciding how to control the risk from a step in a practical that produces fine airborne powder. Using the hierarchy of control, which approach is preferred over issuing dust masks to students?

  1. Relying on students to stand further from the bench
  2. Shortening the time students spend on the dusty step
  3. Providing written instructions on how to wear the mask correctly
  4. Enclosing the powder step or substituting a less dusty form of the material Correct answer.

Explanation

The hierarchy of control ranks elimination, substitution and engineering controls above personal protective equipment because they remove or contain the hazard at its source rather than relying on people. Enclosing the step or using a less dusty material prevents exposure for everyone present. Masks, distance and reduced time are lower-order measures that depend on correct human behaviour.

Question 31Laboratory equipment, instruments and their operation

Which piece of glassware is designed to deliver a single, accurate volume of liquid and is marked with the letters 'TD'?

  1. A conical flask
  2. A graduated cylinder
  3. A beaker
  4. A volumetric pipette Correct answer.

Explanation

Volumetric (bulb) pipettes are calibrated 'to deliver' a single fixed volume, indicated by TD markings, and are far more accurate than measuring cylinders. Beakers and conical flasks carry only approximate graduations intended for rough volumes.

Question 32Laboratory equipment, instruments and their operation

What is the main purpose of a Bunsen burner's air hole?

  1. To adjust the height of the flame above the bench
  2. To secure the burner to the heat-proof mat
  3. To control how much air mixes with the gas before combustion Correct answer.
  4. To regulate the gas cylinder pressure

Explanation

The air hole admits air so it can mix with the gas stream; opening it produces a hotter, non-luminous blue flame, while closing it gives a cooler, luminous yellow flame. This lets the worker choose the flame type needed for the task.

Question 33Laboratory equipment, instruments and their operation

A laboratory balance reads 0.000 g before a weighing boat is placed on it. What should the technician do first?

  1. Record the boat's mass and subtract it later
  2. Recalibrate the balance with certified masses
  3. Move the balance to a different bench
  4. Tare the balance so the boat's mass is excluded Correct answer.

Explanation

Taring resets the display to zero with the container in place, so the reading then shows only the mass of the sample added. This is quicker and less error-prone than manually subtracting a container mass.

Question 34Laboratory equipment, instruments and their operation

Which instrument is most appropriate for measuring the pH of a buffer solution to two decimal places?

  1. A calibrated pH meter with a glass electrode Correct answer.
  2. A burette
  3. Universal indicator paper
  4. A conductivity meter

Explanation

A calibrated pH meter with a glass electrode gives numeric readings to two decimal places and is the standard tool for precise pH measurement. Indicator paper gives only approximate colour-match values.

Question 35Laboratory equipment, instruments and their operation

What does a fume cupboard primarily protect the laboratory worker from?

  1. Thermal burns from hot glassware
  2. Inhalation of hazardous vapours and fumes Correct answer.
  3. Splashes reaching the eyes
  4. Exposure to ultraviolet light

Explanation

A fume cupboard extracts air away from the worker, removing vapours, fumes and aerosols generated by hazardous chemicals. Eye and thermal protection are provided by other controls such as goggles and heat-resistant gloves.

Question 36Laboratory equipment, instruments and their operation

Which glassware should be used to prepare a standard solution of accurately known concentration?

  1. A volumetric flask Correct answer.
  2. A beaker
  3. A test tube
  4. A measuring cylinder

Explanation

A volumetric flask has a single calibration mark at a defined temperature and is designed to contain an exact volume, making it the correct vessel for standard solutions. Other glassware has only approximate graduations.

Question 37Laboratory equipment, instruments and their operation

What is the correct way to read the volume in a measuring cylinder?

  1. From below, reading the base of the cylinder
  2. At eye level, reading the bottom of the meniscus Correct answer.
  3. At arm's length, estimating the nearest mark
  4. From above, reading the top of the meniscus

Explanation

Aligning the eye with the meniscus avoids parallax error, and for most aqueous solutions the bottom of the curve is read. Viewing from above or below shifts the apparent position of the meniscus.

Question 38Laboratory equipment, instruments and their operation

What is the function of a desiccator in the laboratory?

  1. To sterilise glassware before use
  2. To cool hot crucibles rapidly
  3. To keep samples dry by maintaining a low-humidity environment Correct answer.
  4. To store volatile solvents safely

Explanation

A desiccator contains a drying agent such as silica gel and a sealed atmosphere, so hygroscopic samples and dried glassware stay free of moisture. It is not a sterilising or cooling device.

Question 39Laboratory equipment, instruments and their operation

A technician needs to heat a liquid to about 80 °C and hold it steady. Which combination is most suitable?

  1. A water bath with a thermostat and a thermometer Correct answer.
  2. A desiccator and a hot plate
  3. A Bunsen burner with a luminous flame
  4. A heat-proof mat and a watch glass

Explanation

A thermostatted water bath transfers heat gently and holds a set temperature, which suits holding a liquid near 80 °C. A luminous Bunsen flame is sooty and difficult to control at a precise temperature.

Question 40Laboratory equipment, instruments and their operation

During a titration the burette reading is taken at the top of the meniscus rather than the bottom. What is the main consequence?

  1. The burette's calibration becomes invalid
  2. Random error increases but the mean stays unbiased
  3. The indicator endpoint changes colour earlier
  4. A systematic error is introduced into every titre Correct answer.

Explanation

Reading the wrong part of the meniscus shifts every reading by a consistent offset, which is a systematic error rather than random scatter. Because the offset applies to both start and end readings, it may partly cancel in the titre, but the practice is still incorrect and can bias results.

Question 41Laboratory equipment, instruments and their operation

Why must a pH meter be calibrated with fresh buffer solutions before a series of measurements?

  1. To correct the electrode response against known reference pH values Correct answer.
  2. To increase the speed of the reading display
  3. To sterilise the electrode between samples
  4. To remove the need for rinsing the electrode

Explanation

Calibration compares the electrode's output with buffers of known pH so the meter's slope and offset are corrected. This ensures readings are traceable and accurate; it does not sterilise or replace rinsing.

Question 42Laboratory equipment, instruments and their operation

A centrifuge is loaded with six tubes. How should they be arranged?

  1. Tubes of different sizes placed wherever they fit
  2. All six tubes placed on one side of the rotor
  3. Only one tube placed in the centre position
  4. In opposing pairs of equal mass, balanced across the rotor Correct answer.

Explanation

Centrifuge tubes must be arranged symmetrically with matching masses so the rotor is balanced and vibration is avoided. An unbalanced load can damage the rotor and cause the instrument to shut down or fail.

Question 43Laboratory equipment, instruments and their operation

Which action best protects a sensitive analytical balance from drift during use?

  1. Weighing warm objects straight from the oven
  2. Closing the draft shield before each reading Correct answer.
  3. Leaving the side doors open for ventilation
  4. Placing the balance next to a centrifuge

Explanation

Air currents across the pan cause unstable readings, so the draft shield should be closed during measurement. Warm objects also create convection currents that disturb the reading.

Question 44Laboratory equipment, instruments and their operation

What is the purpose of a reflux condenser attached to a round-bottom flask?

  1. To increase the pressure inside the flask
  2. To filter solid impurities from the reaction
  3. To measure the volume of gas produced
  4. To return condensing vapour to the flask while allowing heating Correct answer.

Explanation

A reflux condenser cools rising vapour so it condenses and drips back into the flask, allowing prolonged heating without losing solvent. It does not filter, measure gas, or intentionally raise pressure.

Question 45Laboratory equipment, instruments and their operation

A student uses a volumetric pipette to transfer 25.00 mL but blows the last drop out of the tip. How does this affect the delivered volume?

  1. The delivered volume is slightly less than 25.00 mL
  2. The delivered volume is exactly 25.00 mL
  3. The pipette becomes permanently uncalibrated
  4. The delivered volume exceeds the calibrated volume Correct answer.

Explanation

A 'to deliver' pipette is calibrated to leave a small residual film in the tip, so forcing that drop out adds extra liquid. The delivered volume therefore exceeds the nominal value.

Question 46Laboratory equipment, instruments and their operation

Which piece of equipment is best for measuring the volume of gas evolved in a reaction over time?

  1. A Buchner funnel
  2. A volumetric flask
  3. A desiccator
  4. A gas syringe connected to the reaction vessel Correct answer.

Explanation

A gas syringe collects and measures gas volume directly and can be read at intervals to follow reaction progress. The other items are used for preparing solutions, filtration and drying.

Question 47Laboratory equipment, instruments and their operation

Why is a crucible heated to constant mass before being used to determine the water content of a sample?

  1. To sterilise the crucible for microbiology work
  2. To remove any residual moisture so the starting mass is stable Correct answer.
  3. To increase the crucible's thermal conductivity
  4. To coat the inside with a protective glaze

Explanation

Heating to constant mass drives off absorbed water and volatile residues, giving a reproducible dry starting mass. Without this step, the mass loss attributed to the sample would be inflated.

Question 48Laboratory equipment, instruments and their operation

What is the correct procedure for lighting a Bunsen burner safely?

  1. Hold a lit match above the burner before turning on the gas
  2. Turn on the gas and wait before searching for a match
  3. Open the air hole fully before turning on the gas
  4. Turn on the gas, then immediately ignite with a spark lighter Correct answer.

Explanation

The gas should be turned on and ignited promptly with a spark lighter or lit taper to avoid an accumulation of unburnt gas. Waiting or searching for a match after the gas is on creates an explosion risk.

Question 49Laboratory equipment, instruments and their operation

A technician must accurately dispense 200 µL repeatedly for a microplate assay. Which instrument is most suitable?

  1. A 50 mL burette
  2. A 10 mL measuring cylinder
  3. A Pasteur pipette with a rubber bulb
  4. A calibrated micropipette with the matching tip Correct answer.

Explanation

Micropipettes are designed for accurate delivery of microlitre volumes and use matched disposable tips to prevent contamination. Measuring cylinders and burettes are unsuitable at the 200 µL scale.

Question 50Laboratory equipment, instruments and their operation

What does the 'class' marking (for example Class A) on volumetric glassware indicate?

  1. The date by which the glassware must be replaced
  2. The maximum temperature the glass can withstand
  3. The chemical resistance rating of the glass
  4. The tolerance limits within which the stated volume is accurate Correct answer.

Explanation

Class markings define the accuracy tolerance of the nominal volume, with Class A glassware having tighter tolerances than Class B. They do not describe heat resistance, chemical resistance or expiry.