After draining a 5 mL graduated pipette, a technician sees water droplets clinging to its inner wall instead of an even film, and the delivered volumes are short. The best remedy is:

Clean it with chromic acid or detergent

Rinse it twice with distilled water

Dry it in a hot-air oven before use

Blow out the last drop every time

Why are bilirubin standards kept in amber (low-actinic) glass bottles?

It cuts out light that destroys bilirubin

It withstands rapid heating and cooling

It prevents evaporation of the solvent

It resists attack by alkaline solutions

Volumetric flasks and pipettes are not dried in a hot-air oven because strong heating can:

Permanently change the calibrated volume

Fade the class and volume markings

Make the glass brittle once it cools

Leave an alkaline film inside the glass

Glassware: composition, grades, cleaning and calibration

29 Kerala PSC Lab Technician Gr II practice questions on Glassware: composition, grades, cleaning and calibration, part of Biochemistry. 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 · Hard
After draining a 5 mL graduated pipette, a technician sees water droplets clinging to its inner wall instead of an even film, and the delivered volumes are short. The best remedy is:
1. ARinse it twice with distilled water
2. BDry it in a hot-air oven before use
3. CBlow out the last drop every time
4. DClean it with chromic acid or detergent
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Answer: D · Clean it with chromic acid or detergent
Water that breaks into droplets on glass shows a film of grease or other organic residue on the surface. The droplets stay behind, so less than the marked volume is delivered. Soaking in chromic acid mixture or a laboratory detergent, followed by thorough rinsing with tap water and distilled water, gives a clean surface on which water drains as an unbroken film. Blowing out or drying leaves the grease in place.
- A: Water rinses cannot remove a greasy film.
- B: Heat does not remove grease and can bake it onto the glass.
- C: Blowing out a TD pipette adds its own volume error and leaves the grease behind.
Question 2 · Easy
How does Class A volumetric glassware differ from Class B?
1. AA faster delivery time
2. BThicker and stronger walls
3. CGreater resistance to heat
4. DA narrower volume tolerance
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Answer: D · A narrower volume tolerance
Class A volumetric flasks, pipettes and burettes meet the strictest accuracy standard; the tolerance allowed for Class B items is about twice that of Class A. Class A items are used for preparing standards and wherever an exact volume matters. Each piece is marked with its class, its volume, its calibration temperature and TC or TD. Class B items are adequate for routine reagent preparation.
- A: The class is defined by accuracy; a faster outflow would reduce accuracy.
- B: Wall thickness is not what the accuracy class describes.
- C: Heat resistance depends on the type of glass, not on the accuracy class.
Question 3 · Easy
A pipette marked 'TC', such as the Sahli hemoglobin pipette, is calibrated to:
1. ADeliver it after a set wait
2. BDeliver it after blowing out
3. CDeliver it by free drainage
4. DContain the stated volume
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Answer: D · Contain the stated volume
A TC (to contain) pipette holds the stated volume, and the film left on its wall is part of that volume, so the contents must be rinsed out with the diluent. The 20 µL Sahli pipette is therefore rinsed several times in the acid in the Sahli tube. A TD (to deliver) pipette is calibrated for the volume that drains out, and its last drop is not blown out unless the pipette is marked for blow-out.
- A: A set wait time applies to TD (to deliver) pipettes.
- B: Blow-out pipettes are TD pipettes, marked with a frosted band or double ring.
- C: Free drainage describes a TD (to deliver) pipette.
Question 4 · Easy
Why are bilirubin standards kept in amber (low-actinic) glass bottles?
1. AIt withstands rapid heating and cooling
2. BIt cuts out light that destroys bilirubin
3. CIt prevents evaporation of the solvent
4. DIt resists attack by alkaline solutions
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Answer: B · It cuts out light that destroys bilirubin
Low-actinic glass is coloured amber or red by added metal oxides and absorbs blue and ultraviolet light. Bilirubin is broken down by light in this range, so standards in clear glass lose strength quickly. Other light-sensitive reagents, such as silver nitrate, are stored in amber bottles for the same reason. The colour adds no chemical or heat resistance.
- A: Heat resistance comes from borosilicate composition, not from colour.
- C: Evaporation is prevented by a tight stopper, not by the colour of the glass.
- D: Amber glass is no more resistant to alkali; strong alkali is kept in polythene.
Question 5 · Medium
Volumetric flasks and pipettes are not dried in a hot-air oven because strong heating can:
1. AFade the class and volume markings
2. BPermanently change the calibrated volume
3. CMake the glass brittle once it cools
4. DLeave an alkaline film inside the glass
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Answer: B · Permanently change the calibrated volume
Glass expands when heated and may not return exactly to its original dimensions on cooling, so the volume marked at the calibration temperature can shift. Volumetric glassware is therefore drained and dried at room temperature, or rinsed with acetone or ethanol and air-dried. Beakers, test tubes and other non-volumetric glassware can go into a hot-air oven. For the same reason, hot liquids are never measured in volumetric glassware.
- A: Fired-on markings are not damaged at drying temperatures.
- C: Drying-oven temperatures do not make laboratory glass brittle.
- D: Heating does not create an alkaline film; free alkali is a feature of new soda-lime glass.
Question 6 · Hard
A 5 mL Class A volumetric pipette (tolerance ±0.01 mL) is checked by weighing the water it delivers: 4.982 g at 25 °C, when water density is 0.997 g/mL. Which conclusion is correct?
1. A4.967 mL delivered; outside tolerance
2. B4.982 mL delivered; outside tolerance
3. C4.985 mL delivered; outside tolerance
4. D4.997 mL delivered; within tolerance
Answer and explanation in LearnFree account
Question 7 · Medium
How does chromic acid cleaning mixture (potassium dichromate in concentrated sulphuric acid) remove organic residue from glassware?
1. ABy oxidizing it
2. BBy saponifying it
3. CBy emulsifying it
4. DBy chelating it
Answer and explanation in LearnFree account
Question 8 · Easy
Which oxide, combined with silica, gives heat-resistant glass such as Borosil or Pyrex its low thermal expansion?
1. ALead oxide
2. BSodium oxide
3. CCalcium oxide
4. DBoric oxide
Answer and explanation in LearnFree account
Question 9 · Medium
A colourless solution in a burette is read at the bottom of the meniscus. For a dark solution such as potassium permanganate, the reading is taken at:
1. AThe meniscus seen from above
2. BThe bottom of the meniscus
3. CThe meniscus seen from below
4. DThe top of the meniscus
Answer and explanation in LearnFree account
Question 10 · Medium
Why is new soda-lime glassware soaked overnight in dilute hydrochloric acid before it is first used?
1. ATo harden the glass against heat
2. BTo sterilize it before first use
3. CTo dissolve grease left from manufacture
4. DTo neutralize free alkali on its surface
Answer and explanation in LearnFree account
Question 11 · Medium
Before a burette is filled, it is rinsed with a few millilitres of the titrant itself. This is done to:
1. ACalibrate the burette for that particular solution
2. BBring the glass to room temperature
3. CRemove grease from the stopcock
4. DAvoid diluting the titrant with water left inside
Answer and explanation in LearnFree account
Question 12 · Hard
After the laboratory switches to a new washing powder, inorganic phosphorus reagent blanks read high and every patient's phosphate runs high, while other tests are unaffected. The most likely cause is:
1. APhosphate residue from the detergent on glassware
2. BHemolysis in the patient samples
3. CA wrong wavelength on the colorimeter
4. DA deteriorated molybdate reagent
Answer and explanation in LearnFree account
Question 13 · Easy
How is a graduated pipette with a frosted band or two thin rings near its top meant to be used?
1. ARinsed out with the diluent
2. BBlown out to deliver the last drop
3. CDrained by gravity alone
4. DUsed only to contain a stated volume
Answer and explanation in LearnFree account
Question 14 · Medium
Many laboratories have replaced chromic acid cleaning mixture with laboratory detergents because chromic acid:
1. ALeaves a phosphate film on the glass
2. BCannot remove grease or organic films
3. CDissolves borosilicate glass on contact
4. DContains toxic, carcinogenic hexavalent chromium
Answer and explanation in LearnFree account
Question 15 · Easy
Before routine washing, glassware that held blood or bacterial cultures must first be:
1. AScrubbed with hot detergent and a brush
2. BRinsed under hot tap water
3. CSoaked in chromic acid mixture
4. DAutoclaved or soaked in disinfectant
Answer and explanation in LearnFree account
Question 16 · Medium
Why is a measuring cylinder not used to make up a standard solution?
1. AIt is made only of soft glass
2. BIts volume tolerance is too wide
3. CIt cannot be used with acids
4. DIt is calibrated to deliver, not contain
Answer and explanation in LearnFree account
Question 17 · Easy
Ordinary soft (soda-lime) glass, used for cheap test tubes and microscope slides, is silica fused with:
1. AIron and manganese oxides
2. BBoric and aluminium oxides
3. CLead and potassium oxides
4. DSodium and calcium oxides
Answer and explanation in LearnFree account
Question 18 · Medium
The Ostwald-Folin pipette has its bulb close to the tip. What is it best suited to measure?
1. AVolatile solvents such as ether
2. BLarge volumes of reagent
3. CHot solutions from a water bath
4. DViscous fluids such as blood or serum
Answer and explanation in LearnFree account
Question 19 · Easy
At what standard reference temperature is most volumetric glassware calibrated?
1. A4 °C
2. B0 °C
3. C37 °C
4. D20 °C
Answer and explanation in LearnFree account
Question 20 · Hard
To dilute blood for hemoglobin, a technician fills a 20 µL 'TC' capillary pipette and expels it into the diluent, but does not rinse the pipette in the diluent. The hemoglobin result will be:
1. ARandomly high or low
2. BFalsely high
3. CUnaffected
4. DFalsely low
Answer and explanation in LearnFree account
Question 21 · Hard
A technician rinses a clean bulb pipette with distilled water and, without drying it, at once pipettes the glucose standard. Patient samples are pipetted with a dry pipette. How are the patient results affected?
1. ARandomly scattered
2. BUnchanged
3. CFalsely high
4. DFalsely low
Answer and explanation in LearnFree account
Question 22 · Easy
Glassware for serum iron or zinc estimation is best cleaned by a final soak in:
1. ADilute nitric acid, then deionized water
2. BChromic acid, then tap water
3. CTap water and laboratory detergent
4. D70% ethanol, then air drying
Answer and explanation in LearnFree account
Question 23 · Easy
A bulb (volumetric) pipette marked 'TD' has drained against the wall of the vessel. What is done with the small drop left in its tip?
1. AIt is shaken out
2. BIt is left in the tip
3. CIt is blown out
4. DIt is rinsed out with water
Answer and explanation in LearnFree account
Question 24 · Medium
How does a serological pipette differ from a Mohr (measuring) pipette?
1. AIt is calibrated to contain its volume
2. BIt has a single mark on a narrow stem
3. CIts bulb lies close to the delivery tip
4. DIts graduations run down to the tip
Answer and explanation in LearnFree account
Question 25 · Easy
Which plastic is used for labware that must be sterilized repeatedly in the autoclave?
1. ALow-density polyethylene
2. BPolystyrene
3. CPolypropylene
4. DPolyvinyl chloride
Answer and explanation in LearnFree account

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Glassware: composition, grades, cleaning and calibration

After draining a 5 mL graduated pipette, a technician sees water droplets clinging to its inner wall instead of an even film, and the delivered volumes are short. The best remedy is:

How does Class A volumetric glassware differ from Class B?

A pipette marked 'TC', such as the Sahli hemoglobin pipette, is calibrated to:

Why are bilirubin standards kept in amber (low-actinic) glass bottles?

Volumetric flasks and pipettes are not dried in a hot-air oven because strong heating can:

A 5 mL Class A volumetric pipette (tolerance ±0.01 mL) is checked by weighing the water it delivers: 4.982 g at 25 °C, when water density is 0.997 g/mL. Which conclusion is correct?

How does chromic acid cleaning mixture (potassium dichromate in concentrated sulphuric acid) remove organic residue from glassware?

Which oxide, combined with silica, gives heat-resistant glass such as Borosil or Pyrex its low thermal expansion?

A colourless solution in a burette is read at the bottom of the meniscus. For a dark solution such as potassium permanganate, the reading is taken at:

Why is new soda-lime glassware soaked overnight in dilute hydrochloric acid before it is first used?

Before a burette is filled, it is rinsed with a few millilitres of the titrant itself. This is done to:

After the laboratory switches to a new washing powder, inorganic phosphorus reagent blanks read high and every patient's phosphate runs high, while other tests are unaffected. The most likely cause is:

How is a graduated pipette with a frosted band or two thin rings near its top meant to be used?

Many laboratories have replaced chromic acid cleaning mixture with laboratory detergents because chromic acid:

Before routine washing, glassware that held blood or bacterial cultures must first be:

Why is a measuring cylinder not used to make up a standard solution?

Ordinary soft (soda-lime) glass, used for cheap test tubes and microscope slides, is silica fused with:

The Ostwald-Folin pipette has its bulb close to the tip. What is it best suited to measure?

At what standard reference temperature is most volumetric glassware calibrated?

To dilute blood for hemoglobin, a technician fills a 20 µL 'TC' capillary pipette and expels it into the diluent, but does not rinse the pipette in the diluent. The hemoglobin result will be:

A technician rinses a clean bulb pipette with distilled water and, without drying it, at once pipettes the glucose standard. Patient samples are pipetted with a dry pipette. How are the patient results affected?

Glassware for serum iron or zinc estimation is best cleaned by a final soak in:

A bulb (volumetric) pipette marked 'TD' has drained against the wall of the vessel. What is done with the small drop left in its tip?

How does a serological pipette differ from a Mohr (measuring) pipette?

Which plastic is used for labware that must be sterilized repeatedly in the autoclave?