Supplemental Homework Questions 2013 PDF

Preview

Summary

hw work...

Description

Supplemental Homework Questions These are old exam questions written by Dr. Mathews that she has used in previous years. The problems are divided into chapters matching the book’s chapter numbers, and the chapters are arranged in order in which they are covered in lectures (see syllabus). The problems are multiple choice, short answer, essay, and mathematical chemistry problems. Chapter 3: Experimental Error 1. The answer to the calculation

(1.025)(1.63)(94.0 + 18.13 − 4.6) = 20.12949552 8.925 To the correct number of significant figures is? _______________________________________________________________ 2. The result of adding 1.17x10-2 and 8x10-3 is to the correct number of significant figures is? _______________________________________________________________ 3. The calculation below, when expressed to the correct number of significant figures and properly rounded should be written as? (107.36 - 99.2)(5.4033x105) = 4.4090928 x 106 _______________________________________________________________ 4. In which of the following are all of the zeros significant? A. B. C. D. E.

100.090090 143.29 0.05843 0.1000 00.0030020

Supplemental*Problems*CHM*2280*

*

1*

5. Calculate the answer to the following calculation with the proper number of significant figures. (0.002843 * 12.80184) / 0.00032 = A. B. C. D. E.

113.73635 113.736 113.74 113.7 1.1 x 102

6. Do the indicated arithmetic and give the answer to the correct number of significant figures. A. (8.71 x 0.0301) / 0.031 = __________

B. 0.71 + 92.2 = __________ C. (934 * 0.00435) + 107 = __________

Chapter 6: Chemical Equilibrium 7. (For the following chemical reaction, ΔH = +2816 kJ: 6CO2 (g) + 6H2O (l) ⇔ C6H12O6 (s) + 6O2 (g) Indicate how the equilibrium yield of C6H12O6 is affected by the following disturbances. Indicate decrease, increase, or no change in the yield of C6H12O6. a. increasing PCO2 b. increasing temperature c. removing CO2 d. decreasing the total pressure e. removing part of the C6H12O6 f. adding a catalyst _______________________________________________________________

Supplemental*Problems*CHM*2280*

*

2*

8. The Haber Process for the production of ammonia involves the following equilibrium. N2 (g) + 3H2 (g) ⇔ 2NH3 (g)

ΔH = -92.38 kJ/mol ΔS= -198.4 J/K·mol

a. Calculate the values of ΔGº for the reaction at 25ºC and 500ºC (assume ΔH and ΔS values do not change with temperature). Express your answer in J/mol. Hint: The Universal gas constant, R = 8.314 J/K·mol, and 0ºC = 273.15 K). Report your answer to 2 significant figures. b. At what temperature is the reaction favored?

c. Calculate the equilibrium constant Keq at 25ºC for the reaction involved in the Haber Process.

d. Indicate weather the products or reactants are favored. _______________________________________________________________ 9. The Ksp for PbSO4 is 6.3 x 10-7 at 25ºC. Assuming that PbSO4 dissociates completely upon dissolving and that there are no other important equilibria affecting its solubility, calculate the solubility of PbSO4 in grams per liter. _______________________________________________________________ 10. What is the conjugate base of each of the following acids? a. PH4+ b. HCO3_______________________________________________________________ 11. What is the conjugate acid of each of the following? a. CNb. HCO3-

Supplemental*Problems*CHM*2280*

*

3*

12. Classify the following compounds as weak acids or strong acids: a. Nitrous acid b. hydrocholoric acid

c. hydrofluoric acid d. hypochlorous acid

e. perchoric acid _______________________________________________________________

13. Identify the Lewis acid and Lewis base in the reaction below: (CH3)3N (g) + BF3 (g) → (CH3)3NBF3 (g) _______________________________________________________________

14. Which of the following is(are) a strong electrolyte(s): (i) HF A. B. C. D. E. F.

(ii) CH3COOH

(iii) NH3

(iv) KCl

(v) CH3COONa

i, ii, and iii i, ii, iv, and v i, iv, and v i and ii iv and v iv only

_______________________________________________________________

Supplemental*Problems*CHM*2280*

*

4*

15. A woman straightens up her room. Her action does not violate the second law of thermodynamics because: A. The entropy of her room is increased B. Energy of the universe was conserved C. The entropy increase by the breakdown of nutrients in her body is greater than the entropy decrease by the straightening of her room D. Her action does violate the second law of thermodynamics E. The heat given off by her body from cleaning the room is exothermic _______________________________________________________________ 16. Which one of the following statements is TRUE concerning the acid-base reaction below? (CH3)3N (l) + BF3 (l) ⇔ (CH3)3NBF3 (s) A. (CH3)3N is a Lewis acid and BF3 is a Lewis base B. (CH3)3N is a Lewis base and BF3 is a Lewis acid C. Both reactants are Lewis acids D. Both reactants are Lewis bases E. None of the following statements are true. _______________________________________________________________ 17. Rank the following in order of increasing acid strength. For H2S at 25°C: Ka1 =9.5x10-8, Ka2 = 1.0 x10-19 H2 S A. B. C. D. E.

HS−

S2−

H2S < HS− = S2− S2− = HS− < H2S S2− < HS− = H2S H2S < HS− < S2− S2− < HS− < H2S

_______________________________________________________________

Supplemental*Problems*CHM*2280*

*

5*

18. If each of the following salts is dissolved in water, will the solution be acidic, basic or neutral. Circle the correct answer. A. Na2CO3

ACID

NEUTRAL

BASIC

B. KCl

ACID

NEUTRAL

BASIC

_______________________________________________________________ 19. For the following reactions, label each species an acid or base. Indicate the species that are conjugates of one another: -

-

2 + A. HSO4 + NH3 ⇌ SO4 + NH4

Acid: Conjugate Base: Base: Conjugate Acid: -

-

B. HPO42 + NH4+ ⇌ H2PO4 + NH3 Acid: Conjugate Base:

Base: Conjugate Acid: _______________________________________________________________

Supplemental*Problems*CHM*2280*

*

6*

20. One way to prepare hydrogen is by the decomposition of water: H2O (g) ⇌ 2H2 (g) + O2 (g)

ΔH = +484 kJ

Indicate if the following stresses will shift the equilibrium to the left, to the right, or have no effect. a. Increasing partial pressure of O2 (g): b. Increasing temperature: c. Removing H2 (g): d. Decreasing the total pressure: e. adding a catalyst: _______________________________________________________________ 21. Lead (II) chromate, PbCrO4, was used as a yellow paint pigment (“chrome yellow”). The solubility product for PbCrO4, is Ksp = 1.8 x 10 14. Calculate the molar solubility of PbCrO4. -

B. When a solution is prepare that is 5.0 x 10-4 M in lead ion, Pb2+, and 5.0 x10 5 M -

in chromate ion CrO42 , would you expect the lead (II) chromate to precipitate? _______________________________________________________________ 22. A solution is prepared in which Sr2+ = [Ba2+] = 4.0x10-4 M. NaF is slowly added to the solution at 25°C. The Ksp for BaF2 is 2.4x10-5 and the Ksp for SrF2 is 7.9x10-10 at this temperature. Which of the following is true? I. II. III.

The first compound that will precipitate is SrF2 There is a concentration of F- at which SrF2 will precipitate but not BaF2 There is no concentration of F- at which SrF2 and BaF2 will both precipitate

A. B. C. D. E.

I only II only I and II only II and III only All of the above

Supplemental*Problems*CHM*2280*

*

7*

23. HI is a strong acid whereas HF is a weak acid. Which of the following is NOT true? A. B. C. D. E.

If a 1 M solution of HI is prepared, [I-] is approximately 1 M. For an HF solution at equilibrium, [HF] > [H+] For an HF solution at equilibrium, [H+] > [OH-] A solution of NaF is expected to be basic A solution of NaI is expected to be basic

_______________________________________________________________ 24. Which of the following regarding reaction spontaneity is true? A. A reaction with a positive ΔS° will always be spontaneous. B. A reaction with a negative ΔH° will always be spontaneous. C. A reaction with a positive ΔS° and a negative ΔH° will always be spontaneous. D. A reaction with a negative ΔS° and a negative ΔH° will never be spontaneous. E. A reaction with a positive ΔS° and a positive ΔH° will never be spontaneous. _______________________________________________________________ 25. When a solid sample of NaNO3 is added to a cup of water the temperature of the resulting solution decreases. Which of the following MUST be true? I. II. III.

The entropy of the solution must be positive The entropy of the solution must be negative The enthalpy of the solution must be negative

A. B. C. D. E.

I only II only I and II only II and III only I and III only

Supplemental*Problems*CHM*2280*

*

8*

26. Which of the following salts will produce a solution with a pH of greater than 7 when placed in distilled water? A. B. C. D. E.

NaCN KCl NaNO3 NH4NO3 KI

_______________________________________________________________ 27. For all parts of this problem circle your final answer. Given the following equation: PbI2 (s) ⇌ Pb2+ (aq) + 2I- (aq)

Ksp= 1.4x10-8

A. What is the value of ΔG° for the dissociation of PbI2 at 25°C? Under standard conditions is this reaction spontaneous or not spontaneous. B. The Ksp of lead iodide is 1.4x10-8. What is the solubility of PbI2 in mol/L? C. A solution is prepared by adding 3.0x10-4 moles of PbI2 to distilled water to form 500 mL of solution at 25°C. Will there be a precipitate?

Supplemental*Problems*CHM*2280*

*

9*

28. Methanol is prepared industrially from synthesis gas (CO and H2): CO (g) + H2 (g) ⇌ CH3OH (g)

ΔH = -21.7 kcal

Indicate if the following stresses will shift the equilibrium to the left, to the right, or have no effect OR effect temperature or concentration by increase, decrease or no change. A. If the temperature is decreased: A.1. Equilibrium ________________________________. A.2. [CH3OH] will _______________________________. B. If [H2] increases: B.1. Equilibrium ___________________________. B.2. [CH3OH] will _______________________________. 11B.3. Temperature will ____________________________. C. If catalyst is added: C.1. Equilibrium _____________________________________. C.2. [CH3OH] will ____________________________________. D. If [CH3OH] decreases: D.1. Equilibrium _____________________________________. D.2. [CO] will ______________________________________. D.3. [H2] will _______________________________________.

Supplemental*Problems*CHM*2280*

*

10*

Chapter 7: Activity and the Systematic Treatment of Equilibrium 29. A solution is prepared by mixing 0.0500 M NaNO2 plus 0.100 M HNO2. Write the mass and charge balance equations. _______________________________________________________________ 30. Arrange the following in increasing order of ionic strength for a 0.01 M of: LiF, CaO, Al2O3, Mg(OH)2 _______________________________________________________________ 31. Write the charge balance and mass balance expression(s). Given the following pertinent equilibria in solution are: CuSO4(s) ⇌ Cu2+(aq) + SO42-(aq) SO42-(aq) + H2O (l) ⇌ HSO4-(aq) + OH-(aq) 2 H2O (l) ⇌ H3O+(aq) + OH- (aq) Cu2+ (aq) + OH-(aq) ⇌ CuOH+(aq) CuOH+(aq) + OH-(aq) ⇌ Cu(OH)2(aq) Cu(OH)2(aq) + OH-(aq) ⇌ Cu(OH)3-(aq) Cu(OH)3-(aq) + OH-(aq) ⇌ Cu(OH)42- (aq) _______________________________________________________________ 32. Arrange the following in increasing order of ionic strength for a 1.0 M of: NaNO3, MgSO4, AlCl3, and Ca(ClO4)2. A. NaNO3 < Ca(ClO4)2 < MgSO4 < AlCl3 B. NaNO3 < Ca(ClO4)2 < AlCl3 < MgSO4 C. NaNO3 < < MgSO4 < Ca(ClO4)2 < AlCl3 D. MgSO4 < AlCl3 < Ca(ClO4)2 < NaNO3 E. AlCl3 < MgSO4 < Ca(ClO4)2 < NaNO3

Supplemental*Problems*CHM*2280*

*

11*

33. Consider a buffer solution prepared by mixing 5.00 mmol of Na2C2O4 (sodium oxalate) with 2.50 mmol of HCl in 0.100L. The following species are in solution: Na+, C2O42-, HC2O4-, H2C2O4, Cl-, H+, OH-, and H2O. What is the charge balance equation for the solution? B. Write separate mass balances for Na+, oxalate, and Cl-. Hint: set mass balances equal to their concentrations.

Supplemental*Problems*CHM*2280*

*

12*

Chapter 8: Monoprotic Acid-Base Equilibria 34. Using activities correctly, calculate the pH and concentration of H+ in pure water containing 0.050 M LiBr at 25°C. _______________________________________________________________ 35. The average pH of normal arterial blood is 7.40. At normal body temperature (37°C), Kw = 2.4x10-14. Calculate [H+], [OH-], and pOH and indicate whether the solution is acidic or basic. All concentrations should be reported to 2 significant figures, while pOH values should be reported to 2 decimal places. _______________________________________________________________ 36. HZ is a weak acid. An aqueous solution of HZ is prepared by dissolving 0.0200 mol of HZ in sufficient water to yield 1.00 L of solution. The pH of the solution was 4.93 at 25ºC. (a) What is the Ka of HZ?

(b) What is the fraction of dissociation (express answer as a percentage)? _______________________________________________________________ 37. What is the pH of a buffer that is 0.12 M in lactic acid (HC3H5O3) and 0.10 M in sodium lactate? For lactic acid, Ka = 1.4 x 10-4. _______________________________________________________________ 38. How many grams of Na2CO3 (FM 105.99) should be mixed with 5.00 g of NaHCO3 (FM 84.01) to produce a 100 mL of buffer with pH of 10.00? (The Ka's of carbonic acid are Ka1 = 4.46 10-7 and Ka2 = 4.69 10-11)? _______________________________________________________________ 39. Nicotinic acid (niacin) is a monoprotic acid with the formula HC6H4NO2. A solution that is 0.012 M in nicotinic acid has a pH of 3.39 at 25°C. What is the acidionization constant, Ka, for this acid? _______________________________________________________________

Supplemental*Problems*CHM*2280*

*

13*

40. Which of the following 0.5 M mixture should be used to make a buffer if the desired pH of the solution is 9.25?

Components CH3COOH/CH3COONa H2CO3/HCO3Na KH2PO4/K2HPO4 HCl/KCl NH4Cl/NH3

A. B. C. D. E.

Ka values for the acid Ka = 1.8 x 10-5 Ka = 4.3 x 10-7 Ka = 6.2 x 10-8 Ka >> 1 Ka = 5.6 x 10-10

CH3COOH/CH3COONa H2CO3/HCO3Na KH2PO4/K2HPO4 HCl/KCl NH4Cl/NH3

_______________________________________________________________ 41. When you exercise, the burning sensation that sometimes occurs in your muscles represents the buildup of lactic acid (H2C3H5O3). In a 0.20 M aqueous solution, lactic acid is 2.6% dissociated. What is the value of Ka for this acid? A. B. C. D. E.

4.3 x 10-6 8.3 x10-5 1.4 x10-4 5.2 x 10-3 9.8 x 10-3

_______________________________________________________________ 42. Which one of the following acids be the best for preparing a buffer of pH 3.10 A. B. C. D. E.

Hydroxybenzene Ka = 1.01x10-10 Propanoic Acid Ka = 1.34x10-5 Cyanoacetic Acid Ka = 3.37x10-3 Sulfuric Acid Ka = 1.03x10-2 None of the above will be suitable.

_______________________________________________________________

Supplemental*Problems*CHM*2280*

*

14*

43. In the following reaction, identify the following: Fe3+ (aq) + 6CN- (aq) ⇌ Fe(CN)63- (aq) Lewis Acid: _________________________________ Lewis Base: _________________________________ B. For the following reactions, label each species an acid or base. Indicate the species that are conjugates of one another: SO3

2-

-

+ NH4+ ⇌ HSO3 + NH3

Acid: ___________________________ Conjugate Base: _______________________

Base: __________________________ Conjugate Acid: _______________________

From the equation in part B which species is amphoteric?__________________

Supplemental*Problems*CHM*2280*

*

15*

Chapter 9: Polyprotic Acid-Base Equilibria 44. Glutamic acid is one of the 20 commonly occurring amino acids with acid ionization constants of Ka1 = 6.91 x 10-3, Ka2 = 5.01 x 10-5, and Ka3 = 1.10 x 10-10. Determine the predominant form of glutamic acid and draw its structure properly indicating the state of protonation of each acidic/basic site. The structure of the neutral form of glutamic acid is provide below.

a. at pH = 3.00 b. at pH = 7.40 c. Monosodium glutamate (MSG; NaHGlu) is a commonly used food additive that is marketed as a flavor enhancer. Calculate the pH of a solution prepared by dissolving 0.0800 moles of glutamic acid (H2Glu) and 0.02 moles of the monosodium glutamate in 2.00 L of water. (give to two decimal places) _______________________________________________________________ 45. The weak dibasic compound B has the following pKb values: pKb1 = 4.00 and pKb2 = 8.00 a. Write down balanced reactions for the first and second base ionizations of dibasic compound B in water. b. Write down the equilibrium expressions for the first and second base hydrolysis of the dibasic compound B. c. Given a 5.00 M solution of compound B, determine the concentration of ALL SPECIES present in solution. (All answers should be expressed with 3 sig figs)

Supplemental*Problems*CHM*2280*

*

16*

46. Isoleucine is one of the 20 commonly occurring amino acids with acid ionization constants of Ka1 = 4.81 x 10-3, and Ka2 = 1.75 x 10-10. Determine the predominant form of isoleucine acid and draw its structure properly indicating the state of protonation of each acidic/basic site. The substituent (‘R group’) for isoleucine is CH(CH3)(CH2CH3). a. at pH = 7.40 b. at pH = 12.00 _______________________________________________________________ 47. Glutamic acid is triprotic amino acid with pKa values of 2.23, 4.42, and 9.95. You are given a 0.100 M solution of it in its fully protonated form (H3A). How many moles of KOH must be added to 100 mL of this solution to make a solution with a pH of 5.00. Report answer to 3 sig figs. _______________________________________________________________ 48. Given a 1.00 M solution of ascorbic acid, H2C6H6O6, determine the concentration of H2A, HA-, and A2-. The weak diprotic acid has the following Ka values: Ka1 = 8.0x10-5 and Ka2 = 1.6x10-12 If you do need to make assumptions it must be clearly stated. pH should be expressed to two decimal places. All answers should be expressed with 3 sig figs. For all parts of this problem circle your final answer. Find the pH of a solution prepared by dissolving 1.00 g of glycine amide hydrochloride (FW 110.54, pKa = 8.20) plus 1.00 g of glycine amide (FW 74.08) in 0.100 L. B. How many grams of glycine amide should be added to 1.00 g of glycine amide hydrochloride to give 100 mL of solution with pH = 8.00? C. What would be the pH of the solution if (A) is mixed with 10.00 mL of 0.100 M NaOH? _______________________________________________________________ 49. When the proton in the COOH group in an amino acid is transferred to the NH2 group of that same amino acid molecule, a(n) ______________________ is formed. A. B. C. D. E.

cation amphoter zwitterion dianion dication

Supplemental*Problems*CHM*2280*