HW 2 - This is for Quantitative analysis. I did not see that option but General CHEM PDF

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This is for Quantitative analysis. I did not see that option but General CHEM is a close second....

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1. The Gaussian distribution is characterized by the A) B) C) D) E)

_ and the

.

mean; precision accuracy; standard deviation mean; standard deviation accuracy; precision precision; standard deviation

2. Which of the statements below are TRUE regarding the mean and standard deviation? (i) (ii) (iii) (iv) A) B) C) D) E)

As the number of measurements increases, ´x approaches  if there is no random error. The square of the standard deviation is the average deviation. The mean is the center of the Gaussian distribution. The standard deviation measures the width of the Gaussian distribution. ii, iii, and iv i, iii, and iv I and ii i, ii, and iv iii and iv

3. Calculate the mean and standard deviation for the results below for the concentration of lead in a soil sample. 23.2 ppm, 20.1 ppm, 24.7 ppm, 19.9 ppm, 21.8 ppm A) B) C) D) E)

21.9  3.4 (n = 5) ppm 21.9  2.0 (n =5) ppm 27.4  2.0 (n = 5) ppm 22.0  1.8 (n = 5) ppm 27.4  4.2 (n = 5) ppm

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4. Which term is INCORRECTLY defined? A) B) C) D) E)

Linear range: the range over which the response of an analytical method is proportional to analyte concentration. Corrected absorbance: the average absorbance of the blanks is subtracted from each measured absorbance. Blank solution: solution containing all reagents and solvents used in the analysis to which no analyte is deliberately added. Standard solutions: solutions for which the standard deviation is known. Dynamic range: concentration range over which there is a measurable response to analyte, though the response is not linear.

5. The absorbance for a dye sample of unknown concentration is measured and the corrected absorbance is 0.5482. Calculate the concentration of the dye sample.

A) B) C) D) E)

0.00065 g/mL 0.00052 g/mL 0.00092 g/mL 0.0011 g/mL 0.00079 g/mL

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6. For the reaction aA(aq) + bB(s) ⇌ cC(l) + dD(g), all of the statements below are TRUE, except:

K=

A) B) C) D) E)

( PD )

d

[A]a concentrations of solutes are expressed in moles per liter. concentrations of gases are expressed in bars. concentrations of pure solids, pure liquids and solvents are omitted because they are negligible. quantities in the equilibrium expression are the ratio of the concentration of the species to the concentration in its standard state.

7. The Keq for the equilibrium below is 5.4 × 1013 at 480.0 °C. 2NO(g) + O2 (g) ⇌ 2NO2(g) What is the value of Keq at this temperature for the following reaction?

NO2(g) A) 5.4 × 10-13 B) 5.4 × 1013 C) 1.4 × 10-7 D) 5.66 × 10-3 E) none of the above

1 NO(g) + 2

O2(g)

8. For a reaction with a Ho = +50 kJ and a So = +100.0 J/K at 25 ℃, Go is and the equilibrium constant is . A) B) C) D) E)

negative; less than 1 negative; greater than 1 positive; less than 1 positive; greater than 1 zero; 1

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9. Which statements below are TRUE for enthalpy and entropy? I II III IV

A) B) C) D) E)

Enthalpy is the heat flow, q, under constant applied pressure. Standard conditions for entropy and enthalpy changes are 1 M concentration, 1 bar pressure and 298.15 K. The entropy change for a system is the amount of energy, at a given temperature, that is dispersed into motion of the molecules in the system. When the value of H is negative, heat is released. When the value of S is negative, entropy is increased. I, II and III I, III and IV II and IV III and IV None of the above combinations is true.

10. For the reaction HCN(aq) + H2O(l) ⇌ CN-(aq) + H3O+(aq), all of the following will shift the equilibrium toward the products, except: I II III IV

adding HCN. adding H2O. removing CN−. removing H3O+.

A) B) C) D) E)

I II I, III, and IV II and IV III

11. In which solution is solubility of silver chloride the least? A) B) C) D) E)

Pure water 0.05 M CaCl2 0.10 M NaCl 0.10 M FeCl3 0.15 M AgNO3

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12. The value of ΔG° for a reaction conducted at 25 °C is 2.8 kJ/mol. The equilibrium constant for a reaction is ________ at this temperature. A) 1.13 B) -4.2 C) 0.32 D) -1.13 E) More information is needed.

13. The pH of a solution is 9.65. The solution is hydroxide concentration is A) B) C) D) E)

and the than the hydronium concentration.

acidic; less acidic; greater neutral; equal basic; greater basic; less

14. A chemical equilibrium 2A(aq) ⇌ B(aq) has a forward rate constant, kf = 10 M –1s–1, and a reverse rate constant, kr = 5.0 s–1. What is the value of the equilibrium constant for this system?

A) 0.5 B) 2.0 C) 20

D) 0.050 E) 5.0

15. Which reaction produces a decrease in the entropy of the system? A) 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) B) Na(s) + ½Cl2(g) → NaCl(s) C) 2HgO(s) → 2Hg(l) + O2(g) D) UF6(s) → U(s) + 3F2(g) E) H2O(s) → H2O(g) 5

16. When a system is at equilibrium, ________. A) the reverse process is spontaneous but the forward process is not B) the forward and the reverse processes are both spontaneous C) the forward process is spontaneous but the reverse process is not D) the process is not spontaneous in either direction E) both forward and reverse processes have stopped

17. A reaction that is not spontaneous at low temperature can become spontaneous at high temperature if ΔH is ________ and ΔS is ________. A) +, + B) -, C) +, D) -, + E) +, 0

18. Given the thermodynamic data in the table below, calculate the equilibrium constant (at 298 K) for the reaction: 2 SO2(g) + O2(g) ⇌ 2 SO3(g)

A) 2.40 × 1024 B) 1.06 C) 1.95 D) 3.82 × 1023 E) More data are needed.

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19. Of the following, the entropy of ________ is the largest. A) B2F4 (g) B) BF3 (g) C) B2H6 (g) D) BCl3 (l) E) B2O3 (s)

20. The standard Gibbs free energy of formation of ________ is zero. (a) H2O(l) (b) Fe(s) (c) I22(s) A) (a) only B) (b) only C) (c) only D) (b) and (c) E) (a), (b), and (c)

21.For the reaction C(s) + H2O(g) → CO(g) + H2(g) ΔH° = 133.3 kJ/mol and ΔS° = 121.6 J/K ∙ mol at 298 K. At temperatures greater than ________ °C this reaction is spontaneous under standard conditions. A) 273 B) 823 C) 325 D) 552 E) 1096

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22. ΔH for an endothermic process is ________ while ΔH for an exothermic process is ________. A) zero, positive B) zero, negative C) positive, zero D) negative, positive E) positive, negative

23. Which one of the following statements is true? A) Enthalpy is an intensive property. B) The enthalpy change for a reaction is independent of the state of the reactants and products. C) Enthalpy is a state function. D) H is the value of q measured under conditions of constant volume. E) The enthalpy change of a reaction is the reciprocal of the ΔH of the reverse reaction.

24. The normal boiling point of C2Cl3F3 (MM = 187.375 g/mol) is 47.6 °C and its molar enthalpy of vaporization is 27.49 kJ/mol. What is the change in entropy in the system in J/K when 28.6 grams of C2Cl3F3 vaporizes to a gas at the normal boiling point? A) -13.1 B) -4.19 C) 4.19 D) 27.5 E) 13.1

25. Of the following, ΔH°f is not zero for ________. A) O2(g) B) C(graphite) C) N2(g) D) F2(s) E) Cl2(g)

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26. Consider the following two reactions: A → 2B A → C

ΔH°rxn = 456.7 kJ/mol ΔH°rxn = -22.1 kJ/mol

Determine the enthalpy change for the process: 2B → C A) -478.8 kJ/mol B) -434.6 kJ/mol C) 434.6 kJ/mol D) 478.8 kJ/mol E) More information is needed to solve the problem.

27. For which one of the following equations is ΔH°rxn equal to ΔH°f for the product? A) CH4(g) + 2Cl2(g) → CH2Cl2(l) + 2HCl(g) B) Xe(g) + 2F2(g) → XeF4(g) C) N(g) + O3(g) → N2O3(g) D) 2CO(g) + O2(g) → 2CO2(g) E) C(diamond) + O2(g) → CO2(g)

28. Which of the following occurs when reactants are added to a chemical reaction in solution or the gas phase at equilibrium? A) B) C) D) E)

Q increases and the equilibrium shifts to produce more products. Q increases and the equilibrium shifts to produce more reactants. Q decreases and the equilibrium shifts to produce more products. Q decreases and the equilibrium shifts to produce more reactants. Q is unchanged by the addition of reactants.

29. The acid-dissociation constants of sulfurous acid (H2SO3) are Ka1 = 1.7 × 10-2 and Ka2 = 6.4 × 10-8 at 25.0 °C. Calculate the pH of a 0.163 M aqueous solution of sulfurous acid. A) 4.53 B) 1.28 C) 1.86 D) 6.21 E) 1.93 9

30. Which one of the following statements regarding Kw is false? A) pKw is 14.00 at 25 °C. B) The value of Kw is always 1.0 × 10-14. C) Kw changes with temperature. D) The value of Kw shows that water is a weak acid. E) Kw is known as the ion product of water.

31. An aqueous solution contains 0.150 M HCl at 25.0 °C. The pH of the solution is ________. A) 0.150 B) 1.00 C) 13.00 D) 7.00 E) 0.82

32. The pH of a 0.10 M solution of a weak base is 9.82. What is the Kb for this base? A) 2.1 × 10-4 B) 4.4 × 10-8 C) 8.8 × 10-8 D) 6.6 × 10-4 E) 2.0 × 10-5

33. Which one of the following is the weakest acid? A) HF (Ka = 6.8 × 10-4) B) HClO (Ka = 3.0 × 10-8) C) HNO2 (Ka = 4.5 × 10-4) D) HCN (Ka = 4.9 × 10-10) E) Acetic acid (Ka = 1.8 × 10-5) 10

34. HA is a weak acid. Which equilibrium corresponds to the equilibrium constant Kb for A -? A) HA (aq) + H2O (l) ⇌ H2A+ (aq) + OH-(aq) B) A- (aq) + H3O+ (aq) ⇌ HA (aq) + H2O (l) C) HA (aq) + OH- (aq) ⇌ H2O (l) + H+ (aq) D) A- (aq) + H2O (l) ⇌ HA (aq) + OH- (aq) E) A- (aq) + OH- (aq) ⇌ HOA2- (aq)

35. Using the data in the table, which of the conjugate bases below is the strongest base?

A) OAcB) CHO2C) ClOD) FE) OAc- and CHO2-

36. The acid-dissociation constant, Ka, for gallic acid is 4.57 × 10-3. What is the basedissociation constant, Kb, for the gallate ion? A) 4.57 × 10-3 B) 2.19 × 10-12 C) 5.43 × 10-5 D) 7.81 × 10-6 E) 2.19 × 102

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37. Which of the following aqueous solutions has the highest [OH-]? A) a solution with a pH of 3.0 B) a 1 × 10-4 M solution of HNO3 C) a solution with a pOH of 12.0 D) pure water E) a 1 × 10-3 M solution of NH4Cl

38. What is the pH of an aqueous solution at 25.0 °C that contains 3.98 × 10-9 M hydronium ion? A) 8.400 B) 5.600 C) 9.000 D) 3.980 E) 7.000

39. HZ is a weak acid. An aqueous solution of HZ is prepared by dissolving 0.020 mol of HZ in sufficient water to yield 1.0 L of solution. The pH of the solution was 4.93 at 25.0 °C. The Ka of HZ is ________. A) 1.2 × 10-5 B) 6.9 × 10-9 C) 1.4 × 10-10 D) 9.9 × 10-2 E) 2.8 × 10-12

40. The Ka of hypochlorous acid (HClO) is 3.00 × 10-8. What is the pH at 25.0 °C of an aqueous solution that is 0.0200 M in HClO? A) +2.45 B) -2.45 C) -9.22 D) +9.22 E) +4.61 12

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