A solvent sold as spectroscopic (or HPLC) grade is chosen for photometric work mainly because it has:

Very low absorbance in the UV range

A higher boiling point than usual

A lower price than analytical grade

The glass doors of an analytical balance are closed before reading the weight in order to:

Shield the pan from air currents

Prevent moisture reaching the sample

Protect the user from the chemical

Glass tubes and flasks that held culture or patient blood are handled before routine washing by:

Autoclaving or soaking in disinfectant first

Rinsing under hot tap water first

Soaking straight away in chromic acid

Washing at once with detergent and brush

Glassware, reagents and basic anatomy and physiology

35 Lab technician recruitment practice questions on Glassware, reagents and basic anatomy and physiology, part of Laboratory Management and Safety. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
A solvent sold as spectroscopic (or HPLC) grade is chosen for photometric work mainly because it has:
1. AVery low absorbance in the UV range
2. BA higher boiling point than usual
3. CA lower price than analytical grade
4. DA built-in pH buffer
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Answer: A · Very low absorbance in the UV range
Spectroscopic and HPLC grade solvents are purified to remove traces that absorb ultraviolet light, and the label states the wavelength below which the solvent itself absorbs (its UV cut-off). A solvent with absorbing impurities raises the blank and the baseline, so readings at low wavelengths become unreliable. These grades cost more than ordinary analytical grade. Their boiling point and pH are those of the pure solvent.
- B: Boiling point is a property of the solvent, not of its purity grade.
- C: Spectroscopic grade is more expensive, not cheaper, than analytical grade.
- D: These solvents contain no added buffer.
Question 2 · Hard
To prepare 500 mL of 0.1 M potassium dihydrogen phosphate (molecular weight 136) from an LR grade bottle labelled 'assay 98%', how much should be weighed?
1. A13.88 g
2. B6.66 g
3. C6.80 g
4. D6.94 g
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Answer: D · 6.94 g
Mass of pure salt = molarity x molecular weight x volume in litres = 0.1 x 136 x 0.5 = 6.80 g. Only 98% of the weighed powder is the salt, so the mass needed is 6.80 / 0.98 = 6.94 g. Multiplying by 0.98 instead of dividing gives 6.66 g, and ignoring the purity gives 6.80 g. Correcting for a full litre (13.6 / 0.98) gives 13.88 g.
- A: 13.88 g is the purity-corrected mass for 1 litre, not 500 mL.
- B: 6.66 g multiplies by the purity instead of dividing by it.
- C: 6.80 g ignores the 98% assay printed on the label.
Question 3 · Medium
The glass doors of an analytical balance are closed before reading the weight in order to:
1. APrevent moisture reaching the sample
2. BShield the pan from air currents
3. CProtect the user from the chemical
4. DKeep dust off the chemical
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Answer: B · Shield the pan from air currents
An analytical balance reads to 0.1 mg, so even a slight draught pushing on the pan changes the reading and makes it unsteady. Closing the draft shield doors stops air movement, and the reading is taken only when the stability indicator shows a steady value. For the same reason the balance is kept away from fans, air-conditioner vents and doors. Hygroscopic chemicals are protected by a closed weighing bottle, not by the doors.
- A: Moisture uptake is prevented with a closed weighing bottle and quick weighing.
- C: Hazardous chemicals are weighed in a fume hood or with PPE, not behind balance doors.
- D: Dust is a minor concern; the doors are closed mainly to stop air movement.
Question 4 · Medium
Glass tubes and flasks that held culture or patient blood are handled before routine washing by:
1. ARinsing under hot tap water first
2. BAutoclaving or soaking in disinfectant first
3. CSoaking straight away in chromic acid
4. DWashing at once with detergent and brush
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Answer: B · Autoclaving or soaking in disinfectant first
Glassware contaminated with infectious material is decontaminated before anyone washes it, by autoclaving at 121 °C or by soaking in a suitable disinfectant such as 1% hypochlorite. Only then is it cleaned with detergent, rinsed with tap water and finally with distilled water. Rinsing or brushing first spreads organisms and splashes onto the worker. Chromic acid removes organic films but is not a disinfection step.
- A: Rinsing under the tap first splashes infectious material over the sink and worker.
- C: Chromic acid is a cleaning agent for stubborn residue, not the decontamination step.
- D: Brushing before decontamination exposes the washer to live organisms.
Question 5 · Easy
Which grade of chemical is the purest and is used to prepare primary standard solutions?
1. ALaboratory reagent (LR) grade
2. BChemically pure (CP) grade
3. CPrimary standard grade
4. DTechnical (commercial) grade
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Answer: C · Primary standard grade
Primary standard grade chemicals are of very high, certified purity (usually at least 99.95%), stable and non-hygroscopic, so a weighed amount gives an exactly known concentration. They are used to prepare standards against which other solutions are checked. LR and CP grades contain more impurities and are used for routine reagents. Technical grade is the least pure and suits only cleaning or bulk work.
- A: LR grade is suitable for routine reagents but its purity is not certified for standards.
- B: CP grade is purer than technical grade but below analytical and primary standard grades.
- D: Technical grade is the least pure grade, used for cleaning and industrial work.
Question 6 · Medium
Why is a burette rejected for a titration if an air bubble stays in its tip below the stopcock?
1. AThe bubble escapes and adds a false volume
2. BThe bubble hides the end point colour
3. CThe bubble reacts with the titrant
4. DThe bubble changes the titrant's strength
Answer and explanation in LearnFree account
Question 7 · Hard
After a new washing detergent is introduced, serum inorganic phosphorus is high in every sample and the reagent blank turns blue in washed tubes. What is the likely cause?
1. ADelay in separating serum from cells
2. BMolybdate reagent decomposed by light
3. CPhosphate residue left by the detergent
4. DHemolysis in all the serum samples
Answer and explanation in LearnFree account
Question 8 · Medium
When aspirating with an air-displacement micropipette by the forward method, the plunger is pressed to:
1. AThe second stop, then released quickly
2. BThe first stop, then released quickly
3. CThe second stop, then released slowly
4. DThe first stop, then released slowly
Answer and explanation in LearnFree account
Question 9 · Easy
The tare key of an electronic balance is pressed with the empty container on the pan in order to:
1. ASet the display to zero
2. BLock the weighing pan
3. CLevel the balance base
4. DCalibrate the balance against weights
Answer and explanation in LearnFree account
Question 10 · Easy
Which is the lowest-purity grade of chemical, suitable only for jobs such as cleaning and disinfection?
1. AAnalytical reagent grade
2. BSpectroscopic grade
3. CTechnical grade
4. DPrimary standard grade
Answer and explanation in LearnFree account
Question 11 · Easy
Why is a conical (Erlenmeyer) flask used to hold the solution during a titration?
1. AIt protects contents from light
2. BIt can be swirled without spilling
3. CIt holds an exactly calibrated volume
4. DIt resists strong heating best
Answer and explanation in LearnFree account
Question 12 · Easy
Right after use, blood-stained glass pipettes should be placed at once in:
1. AA jar of water or disinfectant
2. BA hot air oven to dry
3. CChromic acid for a few minutes
4. DA dry drawer for later washing
Answer and explanation in LearnFree account
Question 13 · Hard
NaOH is dissolved in about half the water in a 1 L volumetric flask, made up to the mark at once while the solution is still hot, and then cooled. How will its strength compare with the intended value?
1. AContaminated with silica
2. BWeaker than intended
3. CStronger than intended
4. DExactly as intended
Answer and explanation in LearnFree account
Question 14 · Hard
A method calls for 250 mL of 0.1 M copper sulphate, but only the pentahydrate (CuSO4.5H2O, molecular weight 249.7) is in stock; anhydrous CuSO4 is 159.6. How much pentahydrate is weighed?
1. A15.96 g
2. B24.97 g
3. C3.99 g
4. D6.24 g
Answer and explanation in LearnFree account
Question 15 · Medium
A healthy 35-year-old donor has serum potassium 4.6 mmol/L and heparin plasma potassium 4.3 mmol/L from the same draw. Why is the serum value higher?
1. ARed cells take up potassium in serum
2. BPlatelets release potassium during clotting
3. CFibrinogen binds potassium in plasma
4. DHeparin adds potassium to plasma
Answer and explanation in LearnFree account
Question 16 · Hard
A trainee weighs sodium hydroxide pellets on an open watch glass for exact 0.1 N NaOH. Titration against a primary standard shows only 0.093 N. What most likely caused the shortfall?
1. AThe primary standard was weighed in excess
2. BThe watch glass added mass to the reading
3. CThe balance was not tared before weighing
4. DThe pellets took up water and CO2 while weighed
Answer and explanation in LearnFree account
Question 17 · Medium
A healthy 27-year-old woman at 32 weeks of pregnancy has a Westergren ESR of 42 mm in the first hour. Which plasma protein mainly causes this rise?
1. AFibrinogen
2. BInsulin
3. CAlbumin
4. DTransthyretin
Answer and explanation in LearnFree account
Question 18 · Medium
Bottles labelled AR (analytical reagent) grade differ from lower grades mainly in carrying on the label:
1. AThe molecular weight of the chemical
2. BThe date the chemical was manufactured
3. CThe maximum limits of named impurities
4. DThe hazard symbol for the chemical
Answer and explanation in LearnFree account
Question 19 · Medium
A woman whose period is 5 days late has a negative card pregnancy test on an afternoon urine. A repeat on early morning urine is advised because that sample:
1. AHas the most acid pH, which preserves hCG
2. BIs free of bacteria after the night
3. CIs the most concentrated, with the highest hCG
4. DContains no protein that could interfere
Answer and explanation in LearnFree account
Question 20 · Easy
Which adult result lies within its usual reference range?
1. ASerum albumin 2.4 g/dL
2. BSerum potassium 6.2 mmol/L
3. CBlood urea 85 mg/dL
4. DSerum calcium 9.5 mg/dL
Answer and explanation in LearnFree account
Question 21 · Easy
To avoid parallax error when reading the meniscus in a pipette or burette, the eye must be:
1. ASlightly above the meniscus
2. BAt an angle to the meniscus
3. CSlightly below the meniscus
4. DLevel with the meniscus
Answer and explanation in LearnFree account
Question 22 · Easy
Before weighing on an analytical balance, the bubble of the spirit level should be:
1. AOutside the circle
2. BTouching the edge of the circle
3. CMoving freely across it
4. DIn the centre of the circle
Answer and explanation in LearnFree account
Question 23 · Easy
A plain Pasteur pipette is best used to:
1. ATransfer liquid dropwise without measuring
2. BMeasure an exact volume of serum for a test
3. CDilute blood for a red cell count
4. DDeliver a graduated range of volumes
Answer and explanation in LearnFree account
Question 24 · Easy
What is the usual adult reference range for blood urea?
1. A15-40 mg/dL
2. B70-100 mg/dL
3. C150-400 mg/dL
4. D0.6-1.2 mg/dL
Answer and explanation in LearnFree account
Question 25 · Hard
In a dry air-conditioned room, the analytical balance reading for an empty plastic weighing boat keeps drifting and does not settle. The doors are closed and the balance is level. What is the likely cause?
1. AStatic charge on the plastic boat
2. BMoisture uptake by the boat
3. CAn expired calibration certificate
4. DA warm boat heating the air
Answer and explanation in LearnFree account

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Glassware, reagents and basic anatomy and physiology

A solvent sold as spectroscopic (or HPLC) grade is chosen for photometric work mainly because it has:

To prepare 500 mL of 0.1 M potassium dihydrogen phosphate (molecular weight 136) from an LR grade bottle labelled 'assay 98%', how much should be weighed?

The glass doors of an analytical balance are closed before reading the weight in order to:

Glass tubes and flasks that held culture or patient blood are handled before routine washing by:

Which grade of chemical is the purest and is used to prepare primary standard solutions?

Why is a burette rejected for a titration if an air bubble stays in its tip below the stopcock?

After a new washing detergent is introduced, serum inorganic phosphorus is high in every sample and the reagent blank turns blue in washed tubes. What is the likely cause?

When aspirating with an air-displacement micropipette by the forward method, the plunger is pressed to:

The tare key of an electronic balance is pressed with the empty container on the pan in order to:

Which is the lowest-purity grade of chemical, suitable only for jobs such as cleaning and disinfection?

Why is a conical (Erlenmeyer) flask used to hold the solution during a titration?

Right after use, blood-stained glass pipettes should be placed at once in:

NaOH is dissolved in about half the water in a 1 L volumetric flask, made up to the mark at once while the solution is still hot, and then cooled. How will its strength compare with the intended value?

A method calls for 250 mL of 0.1 M copper sulphate, but only the pentahydrate (CuSO4.5H2O, molecular weight 249.7) is in stock; anhydrous CuSO4 is 159.6. How much pentahydrate is weighed?

A healthy 35-year-old donor has serum potassium 4.6 mmol/L and heparin plasma potassium 4.3 mmol/L from the same draw. Why is the serum value higher?

A trainee weighs sodium hydroxide pellets on an open watch glass for exact 0.1 N NaOH. Titration against a primary standard shows only 0.093 N. What most likely caused the shortfall?

A healthy 27-year-old woman at 32 weeks of pregnancy has a Westergren ESR of 42 mm in the first hour. Which plasma protein mainly causes this rise?

Bottles labelled AR (analytical reagent) grade differ from lower grades mainly in carrying on the label:

A woman whose period is 5 days late has a negative card pregnancy test on an afternoon urine. A repeat on early morning urine is advised because that sample:

Which adult result lies within its usual reference range?

To avoid parallax error when reading the meniscus in a pipette or burette, the eye must be:

Before weighing on an analytical balance, the bubble of the spirit level should be:

A plain Pasteur pipette is best used to:

What is the usual adult reference range for blood urea?

In a dry air-conditioned room, the analytical balance reading for an empty plastic weighing boat keeps drifting and does not settle. The doors are closed and the balance is level. What is the likely cause?