CHEMISTRY 100 CHRISTMAS EXAM

Transcription

1 CHEMISTRY 100 CHRISTMAS EXAM Name: ID#: Prof.: PLEASE READ THIS BEFORE YOU BEGIN: This exam comprises 13 pages (including this page) plus a periodic table. Please make sure you have a complete exam and that you have filled in the information above. All questions are to be answered on the question sheets either by circling the appropriate answer on the multiple-choice questions or by writing in your solutions for the short and long answer questions. You may use pen or pencil. Rough calculations can be performed on the foolscap provided. Proper calculators are permitted. You have 2 hours. Some useful constants and equations are given below. Constants R = L-atm/mol-K OR J/mol-K (1 J = 1 kg m 2 s -2 ) Avogadro s number (N) = x mol -1 Atomic mass unit (amu) = x g STP for a gas: 1 atm and 0 C Pa = 1 atm Formulas Quadratic formula: b ± (b 2 4ac) 1/2 2a PV = nrt u = [(3RT)/(M)] ½ ph = pk a + log([base]/[acid])

2 2 (I) Multiple Choice (30 marks, 2 marks each) Please clearly circle the letter of your answer. If two or more answers are circled the question will be marked wrong regardless of whether the correct answer is circled. 1. The density of silver is 10.5 g/cm 3. A piece of silver with a mass of 61.3 g would occupy a volume of cm 3 a) b) 644 c) 10.5 d) e) The net ionic equation for the dissolution of zinc metal in aqueous hydroiodic acid is a) Zn (s) + 2I (aq) ZnI 2 (aq) b) Zn (s) + 2HI (aq) ZnI 2 (aq) + 2H + (aq) c) Zn (s) + 2HI (aq) ZnI 2 (s) + 2H + (aq) d) Zn (s) + 2H + (aq) Zn 2+ (aq) + H 2 (g) e) Zn (s) + H + (aq) Zn 2+ (aq) + H (aq) 3. Which of the following sets of aqueous solutions contains only strong electrolytes? a) HI, HF, H 2 SO 4 b) NaBr, KOH, HNO 2 c) NH 4 Cl, Ba(OH) 2, HClO 4 d) CH 3 COONa, Sr(OH) 2, HNO 3 e) NaOH, HCl, H 3 PO 4 4. Which compound has the atom with the highest oxidation number? a) CaS b) Na 3 N c) MgSO 3 d) Al(NO 2 ) 3 e) NH 4 Cl

3 3 5. The reaction below is exothermic 2SO 2 (g) + O 2 (g) 2SO 3 (g) Which action will increase the number of moles of SO 3 in the reaction container? a) increasing in pressure b) decreasing the pressure c) increasing the temperature d) removing some oxygen e) adding a catalyst 6. Which of the following cannot be an oxidation/reduction reaction? a) combustion reaction b) solubility equilibrium c) decomposition reaction d) combination reaction e) metathesis reaction 7. The value of ΔH for the reaction below is kj: CO (g) + 2H 2 (g) CH 3 OH (l) How many kj of heat are evolved when 5.75 g of CO (g) reacts completely with hydrogen to form CH 3 OH? a) 23.3 b) c) 26.3 d) e) A sample of gas (1.50 mol) is contained in a 15.0 L cylinder. The temperature is increased from 100 C to 150 C. The ratio of final pressure to initial pressure (P 2 /P 1 ) is? a) 1.50 b) c) d) 1.13 e) 1.00

4 4 9. The root-mean-square speed of CO at 113 C is m/s. a) 317 b) 58.3 c) 586 d) 993 e) The adjacent diagram describes a) the titration of a strong acid with a strong base b) the titration of a strong acid with a weak base c) the titration of a weak acid with a strong base d) the titration of a weak acid with a weak base e) the titration of a weak electrolyte with a strong electrolyte 11. An atom of the most common isotope of gold, 197 Au, has protons, neutrons, and electrons. a) 197, 79, 118 b) 118, 79, 39 c) 79, 197, 197 d) 79, 118, 118 e) 79, 118, An ideal gas differs from a real gas in that the molecules of an ideal gas. a) have no attraction for one another b) have appreciable molecular volumes c) have a molecular weight of zero d) have no kinetic energy e) have an average molecular mass

5 5 13. Of the following solutions, which has the greatest buffering capacity? a) M HF and M NaF b) M HF and M NaF c) M HF and M NaF d) M HF and M NaF e) They are all buffer solutions and would have the same capacity. 14. In which of the following aqueous solutions would you expect AgCl to have the lowest solubility? a) pure water b) M BaCl 2 c) M NaCl d) M AgNO 3 e) M KCl 15. In basic solution,. + - a) [H3O ] = [OH ] + - b) [H3O ] > [OH ] + - c) [H3O ] < [OH ] + d) [H3O ] = 0 M e) - [OH ] > 7.00

6 6 (II) Short Answer Questions (20 marks, each worth 4 marks). Answer in the space provided. 1. A 1.00 L solution saturated at 25 C with calcium oxalate (CaC 2 O 4 ) contains g of CaC 2 O 4 in solution. Calculate the solubility-product constant, K sp, for this salt at 25 C. 2. The total volume of seawater on the Earth is 1.5 x L and its density is 1.03 g/l. The seawater contains 3.1% NaCl by mass. Calculate the total mass of sodium chloride in seawater, in kg.

7 7 3. Calculate the molar concentration of Cl ions in an aqueous solution made by adding 200 ml of a 0.15 M solution of NaCl and 150 ml of a 0.18 M solution of CaCl mol of CO and 0.40 mol of H 2 O were placed in a 2.00L reaction vessel. After the following equilibrium is established at a certain temperature, 0.19 mol of CO remain. Calculate K c at this temperature. CO (g) + H 2 O (g) CO 2 (g) + H 2 (g)

8 8 5. The enthalpy of formation of methane is described by the following reaction: C (s) + 2H 2 (g) CH 4 (g) Using the following reactions, calculate ΔH for this reaction: C (s) + O 2 (g) CO 2 (g) ΔH = kj H 2 (g) + ½ O 2 (g) H 2 O (l) ΔH = kJ CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (l) ΔH =

9 9 (III) Longer Questions (50 marks, each worth 10). Answer in the space provided. 1. Balance the following equation in acidic solution and identify the oxidizing and reducing agents. Cr 2 O 7 2+ (aq) + I (aq) Cr 3+ (aq) + I 2 (s) Oxidizing agent Reducing agent

10 10 2. Consider the following reaction: CO(g) + Cl 2 (g) COCl 2 (g) K c = 1.2 x 10 3 at 668K How much of each substance, in moles, will be there at equilibrium in a reaction mixture that initially has mol CO, mol Cl 2 and mol COCl 2 in a 10.0L flask? (HINT: First use the reaction quotient, Q, to determine whether the reaction proceeds from left to right OR right to left)

11 3. An elemental analysis is performed on salicylic acid (which contains C, H and O) in which the compound is combusted in the presence of oxygen. The combustion of 3.00 mg of salicylic acid produces 6.69 mg of CO 2 and 1.17 mg of H 2 O. What is the empirical formula of salicylic acid? 11

12 4. A sample of acetic acid has a ph of Given that the pk a for HC 2 H 3 O 2 is 4.74, what is the initial concentration of the acetic acid? 12

13 13 5. A buffer solution contains 0.12 mol of propionic acid (HC 3 H 5 O 2 ) and 0.10 mol of sodium propionate (NaC 3 H 5 O 2 ) in 1.50 L. (K a for HC 3 H 5 O 2 = 1.3 x 10-5 ). a) What is the ph of this buffer? b) What is the ph of the buffer after the addition of mol of NaOH? (assume that the total volume does not change) c) What is the ph of the buffer after the addition of mol HI? (assume that the total volume does not change)