【GR0627】 The Solution for GRE Chemistry Practice Test [21-40]

The Solution for GRE Chemistry Practice Test [21-40]

 

추천글 : 【GRE】 Solution for GRE Chemistry Practice Test 

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21. Assuming complete dissociation, which of the following is NOT true about a 1.00 M Mg(NO₃)₂ solution? (Molar masses: Mg = 24.30 g; NO₃^- = 62.01 g; Mg(NO₃)₂ = 148.31 g)

 

 

⑴ answer: E

⑵ the amount of NO₃^- : 2 × 6.20 g = 12.40 g

 

 

22. A 499 mg sample of CuSO₄·nH₂O is heated to drive off the waters of hydration and then reweighed to give a final mass of 319 mg. Given that the sample contains 2.0 mmol of Cu, what is the average number of waters of hydration, n, in CuSO₄·nH₂O?

 

 

⑴ answer: B

⑵ H₂O : (499 - 319) g ÷ 18 g/mol = 10 mol

⑶ ∴ n = 10 / 2.0 = 5.0 

 

 

23. Which of the following is the aldol condensation product of butanal (CH₃CH₂CH₂CHO)?

 

 

⑴ answer: E

⑵ aldol condensation 

 

 

 

24. Which of the following statements correctly applies Hückel's rule to the molecules shown below?

 

 

⑴ answer: C

⑵ Hückel's rule 

 

 

25. When 1.0 kJ of heat is added to 5.0 L of an ideal gas, the gas expands against a constant external pressure of 1.0 bar to a final volume of 8.0 L. What is the change in internal energy, ΔU, for the gas? (1.0 L·bar = 0.10 kJ)

 

 

⑴ answer: B

⑵ q = 1.0 kJ = ΔH (∵ constant pressue) = ΔU + PΔV = ΔU + 1.0 × (8.0 - 5.0) × 0.10

⑶ ∴ ΔU = 0.70 kJ

 

 

26. Which of the following must be true for adiabatic processes? 

 

 

⑴ answer: E

 

 

27. At 37 ℃, the dissociation constant, K_w, of water is 2.5 × 10^-14 (pK_w = 13.6). What is the pH of a 1.0 × 10^-5 M NaOH solution at 37 ℃?

 

 

⑴ answer: C

⑵ pOH = 5

⑶ ∴ pH = pK_w - pOH = 13.6 - 5 = 8.6

 

 

28. The reaction shown below is not balanced. If the reaction is balanced using the smallest whole number coefficients possible, the coefficient for I^- will be 

 

 

⑴ answer: D

⑵ oxidation number (ON)

⑶ IO₃^- (I : +5) → 0.5 I₂ (I : 0),   Δ ON = -5

⑷ I^- (I : -1) → 0.5 I₂ (I : 0),    Δ ON = +1

⑸ ⑶ × 1 + ⑷ × 5,   IO₃^- + 5I^- → 3I₂

⑹ complete rxn :   IO₃^- + 5I^- + 6H⁺ → 3I₂ + 3H₂O 

 

 

29. Which of the following is the major product of the reaction shown below?

 

 

⑴ answer: A

⑵ Benzylic carbocation is highly stable compared to other carbocations.

 

 

30. The reaction of 2-bromobutane with methanol, as shown below, yields which of the following as the major product?

 

 

⑴ answer: B

⑵ S_N1 reaction 

 

 

31. Which of the following is the major organic product of the reaction shown below?

 

 

⑴ answer: C

⑵ alcohol S_N2 reaction 

 

 

32. In which of the following are the compounds shown below listed in order of increasing reactivity to acid-catalyzed dehydration?

 

 

⑴ answer: D

⑵ 1 : The secondary carbocation is generated as an intermediate.

⑶ 2 : The tertiary carbocation is generated as an intermediate. 

⑷ 3 : The primary carbocation is generated as an intermediate.

 

 

33. Two cylinders, one containing 1 mole of C₄H₁₀ gas at 1 atm and the other containing 1 mole of CH₄ gas at 1 atm, are at 288 K. If each gas absorbs 100 J of heat under conditions of constant volume, which of the following is true?

 

 

⑴ answer: A

⑵ ΔT = q / nC_V = q / C_V

⑶ C_V for CH₄ = 3/2 RT (cf. only translational movement component)

⑷ C_V for C₄H₁₀ = (3/2 + 3/2 + 1/2) RT (cf. translational (3/2) + rotational (3/2) + vibrational (1/2))

 

 

34. Which of the following statement is true about a pure substance above its critical point? 

 

 

⑴ answer: A

⑵ critical point : The maximum temperature at which liquid can be present.

⑶ triple point : Solid, liquid, and gas are in equilibrium. 

 

 

35. If two wavefunctions Ψ₁(x) and Ψ₂(x) satisfy the condition given below, the two wavefunctions are

 

 

⑴ answer: A

 

 

36. For the equation ÂΨ = aΨ, where  and Ψ are shown be below, all of the following are true EXCEPT:

 

 

⑴ answer: E

 

 

37. At standard temperature and pressure, all of the following compounds exist in the gas state EXCEPT

 

 

⑴ answer: E

⑵ LiH : white clear crystal lumps or powders

 

 

38. The electron configuration of Co in [Co(NH₃)₆]Cl₃ is 

 

 

⑴ answer: E

⑵ the oxidation number of Co = +3

⑶ the neutral state of Co = [Ar]4s²3d⁷

⑷ the state of Co given = [Ar]3d⁶ (∵ 4s orbital electrons dissociate first, and 3d orbital electrons follow.)

 

 

39. A 0.600 g sample of a pure, weak diprotic acid gives end points at 20.0 mL and 40.0 mL when it is titrated with 0.100 M NaOH. What is the molar mass of the weak acid?

 

 

⑴ answer: D

⑵ 0.600 g ÷ x g/mol = 20.0 mL × 0.100 M = 2  mmol

⑶ ∴ x = 0.600 ÷ 0.002 = 300 

 

 

40. The figure shown below is a plot of conductance data obtained during the titration of HCl with a standard solution of NaOH. Which of the following statements about the results is NOT true?

 

 

⑴ answer: D

⑵ conductance = k × ([H⁺] + [Cl^-] + [Na⁺] + [OH^-])

⑶ x = the amount of the standard solution added.

⑷ ([H⁺]₀ + [Cl^-]₀) × V₀ = ([Na⁺]₀ + [OH^-]₀) × V_eq 

⑸ | slope AB | = k × ([H⁺]₀ + [Cl^-]₀) × d/dx [1 - V₀ / (V₀+x) ] 

∵ [H⁺] × V₀ = ([H⁺] + [Na⁺]) × (V₀+x) in AB) 

⑹ | slope BC | = k × ([H⁺]₀ + [Cl^-]₀) × d/dx [1 - V₀ / (V₀+x) ] + k × ([Na⁺]₀ + [OH^-]₀) × d/dx [ (x - V_eq) / (V₀+x) ]

⑺ fact 1. | slope AB | and | slope BC | are not constant.

⑻ fact 2. | d/dx [1 / (1+x)] | decreases as x increases.

⑼ fact 3. At near to B, (x - V_eq) ≪ V_eq. 

 

입력: 2023.06.05 01:38