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1.3 Water & Buffers β Test 1
Q1. Which property is responsible for the cohesive nature of water?β Hydrogen bonds between the O of one water molecule and the H of another
Q2. Water screens electrostatic interactions between dissolved ions because it has:β A high dielectric constant
Q3. A hydrogen bond can form between which pair of atoms?β Hydrogen (bonded to N/O) and nitrogen
Q4. Which statement is true for a hydrogen bond?β ~9% covalent and ~91% electrostatic
Q5. Which statement is true for a hydrogen bond (set 2)?β ~9% covalent and ~91% electrostatic
Q6. Which organic group has the LEAST probability of forming a hydrogen bond with water?β Methyl
Q7. In which case is a hydrogen bond NOT formed?β Between the methyl group of alanine and water
Q8. The forces holding nonpolar regions of molecules together in water are called:β Hydrophobic interactions
Q9. Hydrophobic interactions are exhibited by:β Nonpolar molecules
Q10. Polar molecules dissolve readily in water because:β They can form hydrogen bonds with water
Q11. Which statements are NOT true of water? (i) density maximal at 4Β°C (ii) water dissociates very strongly (iii) high heat of vaporisation (iv) water is nonpolarβ (ii) and (iv)
Q12. The least water-soluble biomolecule among the following is:β Palmitic acid
Q13. Water dissolves charged biomolecules mainly by:β Replacing solute-solute interactions with solute-water (ion-dipole/H-bond) interactions
Q14. Two uncharged atoms are in van der Waals contact when the net:β Attraction is maximum
Q15. Which property makes water a near-universal solvent?β High dielectric constant and H-bonding with solutes
Q16. How many mL of 0.2 M NaOH is needed to neutralise 20 mL of 0.4 N HCl to pH 7.0?β 40 mL
Q17. For ammonia (pKa of NHββΊ β 9.25), the predominant species at pH 4, 8 and 11 respectively is:β NHββΊ, NHββΊ, NHβ
Q18. Which pair is a component of the blood buffer system?β HCOββ» / HβCOβ
Q19. Blood pH is 7.4 when the ratio of HβCOβ to NaHCOβ (carbonic acid : bicarbonate) is:β 1:20
1.3 Water & Buffers β Test 2
Q20. At blood pH 7.4, the ratio of carbonic acid to bicarbonate is:β 1:20
Q21. A buffer has equal concentrations of a weak acid and its conjugate base. Doubling the volume with water, the pH:β Remains almost the same
Q22. Doubling the volume of an equal weak-acid/conjugate-base buffer with distilled water makes the pH:β Remain almost the same
Q23. 50 mL of 2 M KβHPOβ + 25 mL of 2 M KHβPOβ diluted to 250 mL. With pKa β 6.86, the pH is about:β 7.16
Q24. Mixing 100 mL of 0.05 M acetic acid with 100 mL of 0.1 M sodium acetate (pKa 4.76). Final pH?β 5.06
Q25. pH of a solution with 0.2 M acetic acid (pKa 4.7) and 0.1 M sodium acetate?β 4.4
Q26. pH of a buffer with 0.10 M acetic acid and 0.20 M sodium acetate (pKa 4.76)?β 5.1
Q27. Which combination can be used to prepare a buffer solution?β Sodium acetate and acetic acid
Q28. Approximate pH of a 99% dissociated acetic acid solution (pKa 4.76)?β 5.76
Q29. Concentration of formate in 10 mM formic acid at pH 4.15 (pKa formic β 3.75)?β 7.2 mM
Q30. Approximate pH of a 99% dissociated acetic acid solution (Henderson-Hasselbalch, pKa 4.76) (set 2)?β 6.76
Q31. Find the pKa of acid HA if [HA] = 0.90 M and [Aβ»] = 0.30 M at pH 6.0.β 5.52
Q32. The Henderson-Hasselbalch equation is pH = pKa + log of the ratio of:β Conjugate base (proton acceptor) over conjugate acid (proton donor)
Q33. The hydroxyl ion concentration in pure water (25Β°C) is:β 1Γ10β»β· M
Q34. The pH of a solution whose [OHβ»] = 9.31Γ10β»Β² M is approximately:β 12.97
Q35. pH when 20 mL of 1.0 M HNOβ is added to 500 mL water (final ~520 mL)?β 1.4
Q36. The pH of a solution with [HβΊ] = 3.3Γ10β»ΒΉΒ³ M is approximately:β 12.48
Q37. The concentration of HβΊ in a 0.1 M NaOH solution is:β 10β»ΒΉΒ³ M
1.3 Water & Buffers β Test 3
Q38. The concentration of HβΊ in 0.1 M NaOH (set 2) is:β 10β»ΒΉΒ³ M
Q39. Which 100 mM solution will have the LOWEST pH?β NaCl
Q40. A buffer at pH 4.0 is how many times more acidic ([HβΊ]) than the same buffer at pH 6.0?β 100
Q41. Solution A has pH 5.0 and solution B has pH 8.0. Therefore:β A has 1000Γ the [HβΊ] of B
Q42. Buffers A (pH 4.0) and B (pH 6.0). Which statement is true?β [HβOβΊ] in A is 100Γ that in B
Q43. The pH of a phosphate buffer made by mixing 0.2 M NaHβPOβ and 0.2 M NaβHPOβ (pKa 6.86)?β 6.86
Q44. Weak acids A and B have pKa 4 and 6 respectively. Which is correct?β Acid A dissociates more than acid B in water
Q45. Calculate the pKa of lactic acid: [lactic acid] = 0.01 M, [lactate] = 0.087 M at pH 4.8.β 3.3
Q46. Calculate the pKa of lactic acid: [lactic acid] = 0.01 M, [lactate] = 0.087 M at pH 4.8 (set 2).β 3.3
Q47. Which one is EQUAL to the pKa of a weak acid?β The pH at which acid and conjugate base are equal
Q48. Which one is EQUAL to the pKa of a weak acid (set 2)?β The pH where [acid] = [conjugate base]
Q49. The pH of a 10β»βΈ M HCl solution is:β Slightly less than 7
Q50. At physiological pH (~7.4), a protein rich in which amino acid gives maximum buffering capacity?β Histidine
Q51. At blood pH 7.4, the ratio of carbonic acid to bicarbonate is (set 3):β 1:20
Q52. pH of an acetate buffer when [acetate]/[acetic acid] = 10 (pKa 4.76)?β 5.76
Q53. If [HβΊ] = 10β»Β³ M, the [OHβ»] is:β 10β»ΒΉΒΉ M
Q54. Zwitterions are molecules that:β Carry both positive and negative charges simultaneously, with zero net charge
Q55. The buffering capacity of a weak acid/conjugate base buffer is greatest when:β pH equals the pKa