Laboratory basics: glassware, solutions, water and safety

22 Kerala MSc MLT Entrance practice questions on Laboratory basics: glassware, solutions, water and safety, part of Biochemistry. The first 22 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Medium

   Water passed through a mixed-bed ion-exchange (deioniser) cartridge still needs further treatment for some uses. Which contaminants does deionisation remove poorly?

   1. ASodium and chloride ions
   2. BCalcium and magnesium ions
   3. CUncharged organic molecules
   4. DBicarbonate and sulphate ions

   Show answerHide answer

   Answer: C · Uncharged organic molecules

   Ion-exchange resins swap cations for H+ and anions for OH-, so they remove dissolved salts very well. Molecules with no charge, such as many organic compounds, pass through, and bacteria can even grow on the resin bed. Activated carbon, reverse osmosis or distillation and a final filter are added when organic-free or pyrogen-free water is needed. Resistivity measures ions only, so high resistivity does not prove that organics are absent.

   • A: Sodium and chloride are removed by the cation and anion resins.
   • B: Calcium and magnesium are cations and are removed by the cation resin.
   • D: Bicarbonate and sulphate are anions and are exchanged for hydroxide.

2. Question 2 · Medium

   Molal concentration is preferred to molar concentration when colligative properties such as osmolality are calculated, because molality:

   1. AAlready includes the valency of the solute
   2. BIs easier to make up in a volumetric flask
   3. CCounts the solute within the final volume
   4. DDoes not change with temperature

   Show answerHide answer

   Answer: D · Does not change with temperature

   Molality is moles of solute per kilogram of solvent, so it is based on masses, which do not change with temperature. Molarity is moles per litre of solution, and a volume expands or contracts as temperature changes. Freezing-point depression and other colligative properties depend on the number of particles per kilogram of water. That is why osmometers report mOsm/kg.

   • A: Valency enters normality, not molality.
   • B: A molal solution is made by weighing solvent, not by filling a flask to a mark.
   • C: Molarity, not molality, is defined per final volume of solution.

3. Question 3 · Easy

   A graduated pipette has a frosted band etched near its upper end. This band tells the user that the pipette:

   1. AMust be blown out to deliver its full volume
   2. BIs made of heat-resistant borosilicate glass
   3. CIs calibrated to contain, not to deliver
   4. DBelongs to the wider Class B tolerance grade

   Show answerHide answer

   Answer: A · Must be blown out to deliver its full volume

   A frosted band or two thin rings near the top of a pipette mark it as a blow-out pipette. The last drop left in the tip is part of the calibrated volume and must be expelled. Pipettes without this mark are allowed to drain and the tip is touched to the vessel wall, leaving the final drop behind. Blowing out a drain-type pipette gives a volume that is too large.

   • B: The glass type is printed on the pipette, not shown by a frosted band.
   • C: To-contain pipettes are marked TC and are rinsed out, not identified by a frosted band.
   • D: Class A or B is printed as a grade, not shown by the band.

4. Question 4 · Hard

   Benedict's qualitative reagent calls for 17.3 g of crystalline copper sulphate (CuSO4·5H2O, molar mass 249.7) per litre. Only anhydrous CuSO4 (molar mass 159.6) is in stock. How much anhydrous salt gives the same copper content in 1 litre?

   1. A27.1 g
   2. B11.1 g
   3. C6.2 g
   4. D17.3 g

   Show answerHide answer

   Answer: B · 11.1 g

   The copper content must stay the same, so the moles of CuSO4 must match. Moles = 17.3 / 249.7 = 0.0693 mol. Mass of anhydrous salt = 0.0693 x 159.6 = 11.1 g, or simply 17.3 x 159.6 / 249.7. The anhydrous salt is lighter per mole because it carries no water of crystallisation.

   • A: 27.1 g comes from inverting the ratio of molar masses (17.3 x 249.7 / 159.6).
   • C: 6.2 g is the mass of the water of crystallisation in 17.3 g, not the salt.
   • D: Using the same mass ignores the water of crystallisation in the crystalline salt.

5. Question 5 · Medium

   Physiological saline is 0.9% w/v sodium chloride (molar mass 58.5 g/mol). What is its approximate sodium concentration?

   1. A15.4 mmol/L
   2. B90 mmol/L
   3. C308 mmol/L
   4. D154 mmol/L

   Show answerHide answer

   Answer: D · 154 mmol/L

   A 0.9% w/v solution holds 0.9 g per 100 mL, which is 9 g per litre. 9 / 58.5 = 0.154 mol/L, or 154 mmol/L, of NaCl, and each NaCl gives one sodium ion, so sodium is 154 mmol/L. Chloride is also 154 mmol/L, which makes the total about 308 mOsm/L in theory. This is why 0.9% saline is roughly isotonic with plasma.

   • A: 15.4 mmol/L comes from using 0.9 g per litre instead of per 100 mL.
   • B: 90 mmol/L treats 9 g/L as if it were mmol/L after a factor-of-ten slip.
   • C: 308 is the theoretical osmolarity from sodium plus chloride, not the sodium concentration.

6. Question 6 · Hard

   A grossly lipaemic serum is above the linear range for triglycerides. It is diluted as 0.1 mL serum + 0.4 mL saline, then 0.2 mL of this mixture + 0.8 mL saline. The final dilution reads 120 mg/dL. What triglyceride value should be reported?

   1. A1,200 mg/dL
   2. B3,000 mg/dL
   3. C1,920 mg/dL
   4. D600 mg/dL

   Answer and explanation in LearnFree account

7. Question 7 · Medium

   In acid solution, 0.1 M potassium permanganate is 0.5 N. Why is its normality five times its molarity?

   1. AEach permanganate ion gains five electrons
   2. BEach permanganate ion releases five protons
   3. CManganese is in the +7 oxidation state
   4. DTwo permanganate ions oxidise five oxalate ions

   Answer and explanation in LearnFree account

8. Question 8 · Medium

   A mercury thermometer breaks on the laboratory bench, scattering small droplets. The correct clean-up is to:

   1. ARemove the droplets with a laboratory vacuum cleaner
   2. BWash the droplets into the sink with running water
   3. CCover the droplets with sulphur powder and collect them
   4. DWipe the bench with a cloth soaked in hypochlorite

   Answer and explanation in LearnFree account

9. Question 9 · Hard

   How many millilitres of 98% w/w H2SO4 (density 1.84 g/mL, molar mass 98) go into 500 mL of 0.5 N sulphuric acid?

   1. A12.5 mL
   2. B3.4 mL
   3. C6.8 mL
   4. D13.6 mL

   Answer and explanation in LearnFree account

10. Question 10 · Hard

    How much crystalline oxalic acid (H2C2O4·2H2O, molar mass 126) is weighed to prepare 250 mL of 0.1 N oxalic acid for standardising sodium hydroxide?

    1. A1.58 g
    2. B1.13 g
    3. C0.79 g
    4. D3.15 g

    Answer and explanation in LearnFree account

11. Question 11 · Medium

    A freshly made sodium hydroxide solution is called a secondary standard. This means that its exact strength:

    1. AIs fixed by weighing the pellets on an analytical balance
    2. BIs taken from the stated purity on the reagent label
    3. CMust be found by titrating it against a primary standard
    4. DStays constant for a year in a clear glass bottle

    Answer and explanation in LearnFree account

12. Question 12 · Easy

    A standard analytical balance used to weigh primary standards reads to the nearest:

    1. A10 mg (0.01 g)
    2. B1 mg (0.001 g)
    3. C0.1 mg (0.0001 g)
    4. D0.1 g (100 mg)

    Answer and explanation in LearnFree account

13. Question 13 · Medium

    Concentrated hydrochloric acid spills onto a technician's forearm. What is the correct first aid?

    1. AWipe the acid off with a dry cloth and cover it
    2. BFlush with running water for at least 15 minutes
    3. CRub the area with 70% alcohol and then dress it
    4. DApply sodium bicarbonate paste to neutralise it

    Answer and explanation in LearnFree account

14. Question 14 · Easy

    Borosilicate glass (such as Borosil or Pyrex) is preferred for beakers and flasks that are heated, mainly because it has a:

    1. ASurface coating that repels water
    2. BHigher alkali content than soda glass
    3. CHigh lead content that blocks light
    4. DLow coefficient of thermal expansion

    Answer and explanation in LearnFree account

15. Question 15 · Hard

    A patient's serum calcium is 10 mg/dL. The physician wants the result in mEq/L (calcium atomic mass 40, valency 2). What is the value?

    1. A0.5 mEq/L
    2. B25 mEq/L
    3. C2.5 mEq/L
    4. D5.0 mEq/L

    Answer and explanation in LearnFree account

16. Question 16 · Hard

    A technician mixes 100 mL of 10% (w/v) sodium chloride with 300 mL of 2% (w/v) sodium chloride. What is the concentration of the mixture?

    1. A3.2% w/v
    2. B16% w/v
    3. C4% w/v
    4. D6% w/v

    Answer and explanation in LearnFree account

17. Question 17 · Hard

    During a daily balance check, a certified 100.0 mg weight reads 98.1, 98.0, 98.2 and 98.1 mg on four weighings. The balance is level and the draught door is closed. What do these results show?

    1. AAccurate but imprecise; repeat the weighings
    2. BAccurate and precise; continue using it
    3. CImprecise and inaccurate; replace the balance
    4. DPrecise but inaccurate; recalibrate the balance

    Answer and explanation in LearnFree account

18. Question 18 · Easy

    The cobalt-indicating silica gel in a laboratory desiccator has turned from blue to pink. This shows that the silica gel:

    1. AHas absorbed carbon dioxide from the air
    2. BIs fully dry and working at its best
    3. CIs saturated with water and needs drying
    4. DHas reacted with the weighed chemical

    Answer and explanation in LearnFree account

19. Question 19 · Medium

    Glassware used for serum iron and zinc estimation is soaked in dilute nitric or hydrochloric acid and rinsed with deionised water instead of being washed with detergent or chromic acid. Why?

    1. ATo remove metal traces that would raise the results
    2. BTo sterilise the glass before it is used again
    3. CTo etch the glass so that solutions wet it fully
    4. DTo remove grease so that the pipettes drain evenly

    Answer and explanation in LearnFree account

20. Question 20 · Easy

    Type I (reagent-grade) water, used for trace analysis and for preparing standards, should have a resistivity of at least:

    1. A1 MΩ·cm at 25 °C
    2. B0.1 MΩ·cm at 25 °C
    3. C100 Ω·cm at 25 °C
    4. D10 MΩ·cm at 25 °C

    Answer and explanation in LearnFree account

21. Question 21 · Easy

    A 1 N (one normal) solution contains:

    1. AOne gram molecular weight of solute per litre of solution
    2. BOne gram of solute per 100 mL of solution
    3. COne gram molecular weight per kilogram of solvent
    4. DOne gram equivalent of solute per litre of solution

    Answer and explanation in LearnFree account

22. Question 22 · Medium

    A small beaker of ether catches fire on the bench, well away from other solvents. The best immediate action is to:

    1. APour water from a wash bottle onto the flame
    2. BBlow across the beaker to put out the flame
    3. CCover the beaker to cut off the air supply
    4. DCarry the beaker quickly to the sink

    Answer and explanation in LearnFree account