Chem 120 Fritsch

Ch 4 -5 Practice Problems - KEY The following problems are intended to provide you with additional practice in preparing for the exam. Questions come from the textbook, previous quizzes, previous exams, and other sources. Solutions are supplied in a separate document. I will provide the table below in this format on the exam.

Solubility of ionic compounds

Group IA compounds and NH4+ All compounds are soluble and strong electrolytes.

Compounds of NO3-, CH3CO2

-, ClO4- All compounds are soluble and strong electrolytes.

Compounds of Cl-, Br-, I-, CN-, SCN- All compounds are soluble and strong electrolytes except Ag+, Hg2

2+, and Pb2+.

Compounds of SO42- All compounds are soluble and strong electrolytes

except Hg22+ and Pb2+ and Group IIA (Ca to Ra). CaSO4

and Ag2SO4 are sparingly soluble.

Compounds of OH- and S2- All compounds are insoluble and weak or non-electrolytes except those of Group IA and Group IIA (Ca to Ra).

Compounds of CO32-, PO4

3-, AsO43-, CrO4

2- All compounds are insoluble and weak or non-electrolytes except those of Group IA and NH4

+.

1. Which of the following chemical equations is balanced? A. HCl(aq) + NH3(aq) Cl-(aq) + 2NH4

+(aq)

B. 2 SO3(g) + H2O(g) H2S2O8(aq) C. CuCl2(aq) + NaOH(aq) 2NaCl(aq) + Cu(OH)2(aq) D. Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) E. All of the chemical equations are unbalanced. Answer:___D_______

Chem 120 Fritsch

2. In the process of pickling, rust is removed from newly produced steel by washing with hydrochloric acid:

HCl(aq) + Fe2O3(s) FeCl3(aq) + H2O(l) (unbalanced) During the process, some iron is lost as well:

2HCl(aq) + Fe(s) FeCl2(aq) + H2(g) (balanced) a. Which reaction is a reduction-oxidation reaction? b. If only the rust reaction occurred, how many grams of Fe2O3 could be removed with 0.25 L of 1.87 M HCl? c. If only the rust reaction occurred, how many grams of FeCl3 could be produced with 0.25 L of 1.87 M HCl?

Chem 120 Fritsch

3. 8.869 g of an unknown diprotic acid was dissolved in enough water to make a 100 mL solution in a volumetric flask. To 25.00 mL of that solution 62.53 mL of 0.601 M NaOH was added and the phenolphthalein indicator turned pink. a. Find the molar mass (g/mol) of the unknown diprotic acid. b. Propose a molecular formula containing only carbon, hydrogen and oxygen consistent with your answer in part a.

4. What is the major ionic species present in an aqueous solution of Na2SO4. Answer: Na+, SO4

2–

5. During the process of developing black and white film, unexposed silver bromide is removed in a displacement reaction with sodium thiosulfate (Na2S2O3) solution:

AgBr(s) + 2Na2S2O3(aq) Na3Ag(S2O3)2(aq) + NaBr(aq) What volume of a 0.203 M Na2S2O3 solution is needed to remove 3.51 g of AgBr from a roll of film?

Chem 120 Fritsch

6. When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so write the complete ionic equation and the net ionic equation. a. sodium nitrate + copper(II) sulfate b. ammonium iodide + silver nitrate c. potassium carbonate + barium hydroxide d. aluminum nitrate + sodium phosphate e. potassium chloride + iron(II) nitrate f. ammonium sulfate + barium chloride

Chem 120 Fritsch

7. Which the following represents the chemical species present after mixing ammonia and nitric acid? Answer: NH4

+(aq) and NO3

-(aq)

8. Balancing the following redox reactions in acidic solution. a. HNO3(aq) + K2CrO4(aq) + Fe(NO3)2(aq) KNO3(aq) + Fe(NO3)3(aq) + Cr(NO3)3(aq) + H2O(l) b. KClO3(aq) + HBr(aq) Br2(l) + H2O(l) + KCl(aq)

Chem 120 Fritsch

9. What would be the products of the double displacement reaction, when solutions of Li3PO4(aq) and Sr(OH)2(aq) are mixed? Answer: Sr3(PO4)2 will form a precipitate. 10. For the following double displacement reactions, do the following: a. Provide the products of the reaction and balance the chemical equation. b. If a reaction would occur by mixing the reactants together, name the type of reaction for example: precipitation, acid-base neutralization, combustion, etc. c. If a chemical reaction would take place, provide the net ionic equation for that reaction. a. KOH(aq) + FeBr2(aq) b. NH4NO3(aq) + Co(CN)3(aq) c. Mg(OH)2(aq) + HBr(aq)

Chem 120 Fritsch

11. Give the oxidation state of each element in the following reactions. Then, identify the reducing agent and oxidizing agent in each. (All of the reactions are balanced.)

a. 2 MnO4- + 16 H+ + 10 I- 2 Mn2+ + 5 I2 + 8 H2O

Oxidizing agent = MnO4

- reducing agent = I-

b. 6 H+ + Fe2+ + VO43- VO2+ + Fe3+ + 3 H2O

Oxidizing agent = VO4

3- reducing agent = Fe2+ c. Cr6+ + 3 Co2+ Cr3+ + 3 Co3+

Oxidizing agent = Cr6+

reducing agent = Co2+

12. One way of obtaining pure sodium carbonate is through the decomposition of the mineral trona,

which has the formula Na5(CO3)2(HCO3)2H2O. Sodium carbonate is isolated from the balanced reaction below.

2 Na5(CO3)2(HCO3)2H2O(s) 5 Na2CO3(s) + CO2(g) + 3 H2O(g) When 1.00 kg of trona is decomposed, 0.74 kg of Na2CO3 is recovered. What is the percent yield of this reaction?

Chem 120 Fritsch

13. Congratulations, you’ve been hired by the Chemistry Department to prepare the chemicals for G-Chem Lab. This week, 4.6 L of a 0.85 M HCl solution is needed. When you go to the stockroom, you can only find the concentrated HCl solution which is 37% by mass HCl and has a density of 1.1790 g/mL). a. Find the molarity of HCl in the concentrated HCl solution. (Hint: Assume 1 L of solution.) b. Explain how you will prepare the required solution for this week’s lab. Support your explanation with a calculation.

Chem 120 Fritsch

14. Consider the titration of 25.00 mL of 1.21 M phosphoric acid (H3PO4) with 1.36 M barium hydroxide using phenolphthalein as the indicator. a. Give the balanced chemical equation for this reaction including proper phases for all compounds. b. After 29.26 mL of the barium hydroxide solution has been added, what color is the solution, pink or colorless? Justify your answer with calculations.

15. If 10 g of each of the following were placed into 1 L of water, will it be a strong electrolyte, weak electrolyte, or non-electrolyte in solution. Place an X in the appropriate column.

Non-electrolyte Weak electrolyte Strong electrolyte

a. Ag2CO3 X

b. NH3 (ammonia) X

c. C3H6O(acetone) X

d. SrS X

Chem 120 Fritsch

16. An intermediate step in the industrial production of nitric acid involves the reaction of ammonia with oxygen gas to form nitrogen monoxide and water. How many grams of nitrogen monoxide can form by the reaction of 358 g of ammonia with 723 g of oxygen?

17. Calculate each of the following quantities: a. Volume of 1.053 M copper(II) chloride that must be diluted with water to prepare 0.750 L of a 0.5896 M solution. b. Volume of 1.43 M magnesium chloride that must be diluted with water to prepare 530.0 mL of a 4.78 x 10-2 M chloride ion solution. c. Final volume of a 0.0916 M solution prepared by diluting 19.3 mL of 0.378 M sodium carbonate solution.

Chem 120 Fritsch

18. Which of the following reagents will help you separate Ag+

(aq) and Sr2+(aq) ions? (Hint which reagent

will put the ions into different phases based on solubility rules.)

I. KCl (aq) II. KOH (aq) III. K2CO3 (aq) IV. KCN (aq)

A. I and II B. III C. I, II, and IV D. II and IV E. None of the above. Answer:___C_______

Chem 120 Fritsch

19. Which reactant is in excess and what quantity of moles are in excess after the acid-base neutralization reaction of 250 mL of 0.167 M sulfuric acid with 0.100 L of 0.354 M NaOH?

Chem 120 Fritsch

20. In the chemical analysis of an unknown, chemists often add an excess of a reactant, determine the amount of that reactant remaining after the reaction with the unknown and use those amounts to calculate the amoun of unknown. For the analysis of an unknown NaOH solution, you add 50.0 mL of the solution to 0.250 L of an acid solution prepared by dissolving 0.832 g of solid oxalic acid dihydrate (H2C2O4•2H2O) in water. Oxalic acid is a diprotic acid.

2 NaOH(aq) + H2C2O4(aq) Na2C2O4(aq) + 2H2O(l) The unreacted NaOH was titrated with 6.93 mL of 0.169 M HCl. What is the molarity of the original NaOH solution?

Chem 120 Fritsch

21. Consider a titration of 25.00 mL of 1.36 M hydrochloric acid with sodium hydroxide of unknown concentration with phenolphthalein as the endpoint indicator. If with your technique, you let the solution get too pink, too much base added relative to the equivalence point, how would this affect your calculated concentration of the sodium hydroxide solution?

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) A. The calculated concentration will be greater than the actual concentration. B. The calculated concentration will be less than the actual concentration. C. The calculated concentration will be equal to the actual concentration. D. The answer cannot be determined with the information given. Answer:____B______

22. Balance the following acid-base reactions: a. Potassium hydroxide(aq) + hydroiodic acid(aq) b. ammonia(aq) + hydrochloric acid(aq) c. cesium hydroxide(aq) + nitric acid(aq) d. calcium hydroxide(aq) + acetic acid(aq)

23. A 93.22 mL of H2SO4 was titrated with 19.58 mL of 0.1375 M KOH solution. What is the concentration of the H2SO4 solution?

Chem 120 Fritsch

24. Identify the oxidizing agent and reducing agent in each of the following chemical equations: a. Sn(s) + 2H+

(aq) Sn2+(aq) + H2(g)

b. 2H+(aq) + H2O2(aq) + 2Fe2+

(aq) 2Fe3+(aq) + 2H2O(l)

25. Hydrates of ionic compounds (for example MgSO4•7H2O) lose their “waters of hydration” by heating. A 29.66 g sample of copper(II) sulfate was heated and yielded 18.97 g of the anhydrous salt. What is the formula of the hydrate?

Chem 120 Fritsch

26. In a blast furnace, iron oxides are reacted with carbon monoxide to yield iron metal and carbon dioxide. For 293.7 g of the following iron oxides, what mass of carbon oxide would be required to completely consume the iron oxide? a. FeO, wuestite b. Fe2O3, hematite

27. In the process of pickling, rust is removed from newly produced steel by washing with hydrochloric acid:

HCl(aq) + Fe2O3(s) FeCl3(aq) + H2O(l) (unbalanced) During the process, some iron is lost as well:

2HCl(aq) + Fe(s) FeCl2(aq) + H2(g) (balanced) a. Which reaction is a reduction-oxidation reaction? b. If only the rust reaction occurred, how many grams of Fe2O3 could be removed with 0.25 L of 1.87 M HCl? c. If only the rust reaction occurred, how many grams of FeCl3 could be produced with 0.25 L of 1.87 M HCl?

Chem 120 Fritsch

Chem 120 Fritsch

28. Combine the following consecutive reactions to give a single overall reaction. The reactions are not necessarily balanced.

N2(g) + H2(g) 2 NH3(g) 4NH3(g) + O2(g) 4 NO(g) + 6H2O(g)

2NO(g) + O2(g) NO2(g) 3NO2(g) + H2O(l) – 2 HNO3(aq) + NO(g)

Chem 120 Fritsch