Solutions: normal, molar, percentage and dilutions

24 Kerala PSC Lab Technician Gr II practice questions on Solutions: normal, molar, percentage and dilutions, part of Biochemistry. The first 24 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 · Hard

   Concentrated hydrochloric acid is 36% w/w HCl with a specific gravity of 1.18 (HCl molar mass 36.5 g/mol). About how much is needed to make 1 litre of 1 N HCl?

   1. A120 mL
   2. B31 mL
   3. C101 mL
   4. D86 mL

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   Answer: D · 86 mL

   One mL of the acid weighs 1.18 g, of which 36% is HCl: 1.18 × 0.36 = 0.425 g per mL, or 425 g/L. 425 ÷ 36.5 = 11.6 N. Volume needed = (1 N × 1000 mL) ÷ 11.6 N = 86 mL, added to water and made up to 1 litre. Ignoring the specific gravity gives 101 mL, and ignoring the 36% purity gives 31 mL.

   • A: 120 mL divides by the specific gravity instead of multiplying.
   • B: 31 mL ignores the 36% purity, as if the acid were pure HCl.
   • C: 101 mL ignores the specific gravity, treating 36% w/w as 36 g per 100 mL.

2. Question 2 · Medium

   What is the molarity of a 5.85% w/v sodium chloride solution (NaCl molar mass 58.5 g/mol)?

   1. A10 M
   2. B2.0 M
   3. C0.1 M
   4. D1.0 M

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   Answer: D · 1.0 M

   5.85% w/v means 5.85 g per 100 mL, which is 58.5 g per litre. Molarity = g/L ÷ molar mass = 58.5 ÷ 58.5 = 1.0 mol/L. Because NaCl has one replaceable charge, this solution is also 1 N. The general conversion is: molarity = (% w/v × 10) ÷ molar mass.

   • A: 10 M comes from multiplying by 100 instead of 10.
   • B: 2.0 M counts both ions; that approximates the osmolarity, not the molarity.
   • C: 0.1 M comes from taking 5.85 g per litre instead of per 100 mL.

3. Question 3 · Easy

   A 1 molal solution contains 1 mole of solute in:

   1. A1 litre of solvent
   2. B1 kg of solution
   3. C1 litre of solution
   4. D1 kg of solvent

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   Answer: D · 1 kg of solvent

   Molality is moles of solute per kilogram of solvent, so it is based on mass and does not change with temperature. Molarity is moles per litre of final solution, which changes slightly as the solution expands or contracts. Osmolality, measured by freezing point depression, is likewise expressed per kilogram of water. In dilute aqueous solutions molarity and molality are nearly equal.

   • A: Molality uses the mass of solvent, not its volume.
   • B: Molality is per kilogram of solvent, not of the whole solution.
   • C: Moles per litre of solution is molarity.

4. Question 4 · Easy

   What is the strength of the physiological ('normal') saline used in the laboratory?

   1. A1 N NaCl (5.85%)
   2. B0.09% w/v NaCl
   3. C9% w/v NaCl
   4. D0.85-0.9% w/v NaCl

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   Answer: D · 0.85-0.9% w/v NaCl

   Physiological saline contains 0.85-0.9 g of sodium chloride per 100 mL, which is isotonic with plasma, so red cells neither swell nor shrink in it. It is called 'normal' because it matches body fluids, not because it is 1 N. A 1 N NaCl solution (58.5 g/L, 5.85%) is strongly hypertonic. Saline is used to dilute samples and to wash and suspend red cells.

   • A: 'Normal' saline is isotonic, not 1 N; 1 N NaCl is strongly hypertonic.
   • B: 0.09% is hypotonic and would lyse red cells.
   • C: 9% is ten times too strong and hypertonic.

5. Question 5 · Medium

   A 1 M solution of sulphuric acid (H2SO4) has a normality of:

   1. A0.5 N
   2. B1 N
   3. C4 N
   4. D2 N

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   Answer: D · 2 N

   Normality = molarity × the number of replaceable H+ ions per molecule. Sulphuric acid gives two H+ ions, so its equivalent weight is 98 ÷ 2 = 49 g, and a 1 M solution (98 g/L) is 2 N. For monoprotic HCl, molarity and normality are the same. A 1 N solution of sulphuric acid therefore contains 49 g of H2SO4 per litre.

   • A: 0.5 N comes from dividing by 2 instead of multiplying.
   • B: 1 N would be right only for an acid with one replaceable H+.
   • C: 4 N doubles twice; sulphuric acid has only two replaceable H+.

6. Question 6 · Easy

   What does a 10% w/v solution of a solid contain?

   1. A10 mL in 100 mL of solution
   2. B10 g in 100 g of solution
   3. C10 g in 100 mL of water
   4. D10 g in 100 mL of solution

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7. Question 7 · Hard

   A very high serum glucose is diluted: 0.1 mL serum + 0.4 mL saline, then 0.2 mL of this mixture + 0.8 mL saline. The final dilution reads 36 mg/dL. What is the serum glucose?

   1. A180 mg/dL
   2. B360 mg/dL
   3. C576 mg/dL
   4. D900 mg/dL

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8. Question 8 · Medium

   How much 95% ethanol is needed to prepare 500 mL of 70% ethanol?

   1. A679 mL
   2. B475 mL
   3. C350 mL
   4. D368 mL

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9. Question 9 · Medium

   Physiological saline (0.9% w/v NaCl, molar mass 58.5 g/mol) contains about how much sodium per litre?

   1. A308 mmol
   2. B15.4 mmol
   3. C9 mmol
   4. D154 mmol

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10. Question 10 · Easy

    A 1 N (normal) solution contains one gram-equivalent weight of solute in:

    1. A1 kilogram of solvent
    2. B100 mL of solution
    3. C1 litre of solvent
    4. D1 litre of solution

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11. Question 11 · Medium

    Normal saline is 0.9% w/v NaCl (molar mass 58.5 g/mol). Its approximate osmolarity is:

    1. A308 mOsm/L
    2. B616 mOsm/L
    3. C154 mOsm/L
    4. D900 mOsm/L

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12. Question 12 · Easy

    A solution labelled '70% v/v ethanol' contains:

    1. A70 g ethanol in 100 mL of solution
    2. B70 mL ethanol plus 100 mL of water
    3. C70 g ethanol in 100 g of solution
    4. D70 mL ethanol in 100 mL of solution

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13. Question 13 · Medium

    A stock of 10 N NaOH is on the shelf. To make 0.1 N NaOH for titration, how many millilitres of stock go into a 500 mL volumetric flask?

    1. A50 mL
    2. B10 mL
    3. C5 mL
    4. D0.5 mL

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14. Question 14 · Medium

    In a titration, 20 mL of sodium hydroxide is exactly neutralized by 25 mL of 0.1 N hydrochloric acid. What is the normality of the sodium hydroxide?

    1. A0.08 N
    2. B0.125 N
    3. C0.1 N
    4. D0.25 N

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15. Question 15 · Medium

    In a doubling dilution series, tube 1 holds serum diluted 1 in 2 and each tube is diluted 1 in 2 from the one before. The dilution in tube 6 is:

    1. A1 in 12
    2. B1 in 64
    3. C1 in 32
    4. D1 in 128

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16. Question 16 · Hard

    A technician has 50% and 10% solutions of the same salt and needs 200 mL of a 20% solution. What volumes should be mixed?

    1. A150 mL of 50% + 50 mL of 10%
    2. B50 mL of 50% + 150 mL of 10%
    3. C40 mL of 50% + 160 mL of 10%
    4. D100 mL of 50% + 100 mL of 10%

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17. Question 17 · Hard

    A bottle of concentrated sulphuric acid is labelled 98% w/w, specific gravity 1.84 (molecular weight 98). What is its approximate molarity?

    1. A1.84 M
    2. B36.8 M
    3. C10 M
    4. D18.4 M

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18. Question 18 · Hard

    How much oxalic acid dihydrate (H2C2O4·2H2O, molecular weight 126) must be weighed to prepare 250 mL of 0.1 N oxalic acid as a primary standard?

    1. A3.15 g
    2. B1.575 g
    3. C6.3 g
    4. D1.125 g

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19. Question 19 · Easy

    To prepare a 1 in 10 dilution of serum, 0.1 mL of serum is mixed with:

    1. A10 mL diluent
    2. B1.0 mL diluent
    3. C0.09 mL diluent
    4. D0.9 mL diluent

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20. Question 20 · Easy

    In dilute aqueous solutions, a concentration of 1 part per million (ppm) is equal to:

    1. A1 g/L
    2. B1 mg/dL
    3. C1 µg/L
    4. D1 mg/L

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21. Question 21 · Medium

    A 0.1 N sodium hydroxide solution (equivalent weight 40) expressed as a percentage w/v is:

    1. A0.4%
    2. B4%
    3. C0.04%
    4. D40%

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22. Question 22 · Easy

    A patient is given an intravenous dextrose infusion that neither swells nor shrinks red cells. Its strength is:

    1. A0.9% glucose
    2. B10% glucose
    3. C5% glucose
    4. D25% glucose

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23. Question 23 · Medium

    How much sodium hydroxide (molecular weight 40) must be weighed to prepare 250 mL of a 0.1 M solution?

    1. A0.4 g
    2. B4.0 g
    3. C1.0 g
    4. D10.0 g

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24. Question 24 · Easy

    The gram-equivalent weight of sulphuric acid (H2SO4, molecular weight 98) is:

    1. A32.7 g
    2. B196 g
    3. C98 g
    4. D49 g

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