DEPARTMENT OF CHEMISTRY AND CHEMICAL TECHNOLOGY GENERAL CHEMISTRY 202-NYA-05 21, 22 TEST 2 30-OCT-2012 INSTRUCTOR: I. DIONNE.

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1 DEPARTMENT OF CHEMISTRY AND CHEMICAL TECHNOLOGY GENERAL CHEMISTRY 202-NYA-05 21, 22 TEST 2 30-OCT-2012 INSTRUCTOR: I. DIONNE Print your name: Answers INSTRUCTIONS: Answer all questions in the space provided. 1. Duration of this test is 75 minutes. 2. No books or extra paper are permitted. 3. Answer the questions in ink in order to preserve the right to grieve. 4. In order to obtain full credit for your answers, you must clearly show your work. Answers to problems involving calculations must be expressed to the correct number of significant figures and proper units. 5. Calculators may not be shared. Programmable calculators are not permitted. 6. Your attention is drawn to the College policy on cheating. This policy will be enforced. 7. A Periodic Table with constants is provided. Problem 1: /3 Problem 6: /4 Problem 2: /3 Problem 7: /3 Problem 3: /11 Problem 8: /11 Problem 4: /3 SF and Units /2 Problem 5: /3 Total: /43

2 PROBLEM 1 A student has mg of solid Ba(OH) 2 8H 2 O and wants to make a solution of M OH. How much water (in ml) must the student add to obtain such a solution? mg = x 10 2 g MM of Ba(OH) 2 8H 2 O = g/mol x 10 2 g / g/mol = x 10 4 mol we have 2 mol of OH per molecule, therefore mg contains 2 x x 10 4 mol of OH Molarity = moles per liter of solution volume = x 10 4 mol of OH / M volume = x 10 3 L = ml 2.64 ml PROBLEM 2 A 5.30-g sample of NaOH is placed in a 1.00-L volumetric flask and water is added to the mark. A mL sample of the resulting solution is placed in a mL volumetric and diluted to the mark with water. What volume of the second sample is needed to neutralize 33.0 ml of M H 2 SO 4? 5.30 g / g/mol = mol NaOH mol NaOH in 1.00 L = M NaOH Take ml: L x M = mol NaOH Place in ml: mol / L = M 2NaOH + H 2 SO 4 Na 2 SO 4 + H 2 O (l) H 2 SO 4 : M x L = mol NaOH: need mol and the molarity is M volume = mol / M = L L or 54.8 ml Page 2

3 PROBLEM 3 (11 marks) Short-answer questions. (a) Specify what ions are present in solution upon dissolving each of the following substances in water: i. ZnCl 2 Zn 2+ and Cl ii. (NH 4 ) 2 SO 4 NH 4 + and SO 4 2 (b) Predict whether each of the following compounds is soluble or insoluble in water: i. MgBr 2 soluble iii. (NH 4 ) 2 CO 3 soluble ii. PbI 2 iv. Sr(OH) 2 insoluble soluble (c) Identify the precipitate (if any) that forms when the following aqueous solutions are mixed: i. NaNO 3 and NiSO 4 none ii. FeSO 4 and Pb(NO 3 ) 2 PbSO 4 (d) Identify the spectator ions in any reactions that may be involved when each of the following pairs of solutions are mixed: i. Na 2 CO 3 and MgSO 4 Na + and SO 4 2 ii. Pb(NO 3 ) 2 and Na 2 S Na + and NO 3 (e) Indicate the oxidation state of S in each of these species: i. H 2 S 2 iii. SCl ii. S 8 0 iv. SO 3 +4 Page 3

4 (f) Identify the oxidizing and reducing agents in the following reaction: 5H 2 C 2 O 4 + 2MnO 4 + 6H + 2Mn CO 2 (g) + 8H 2 O (l) Oxidizing agent: MnO 4 Reducing agent: H 2 C 2 O 4 (g) Which element is oxidized and which is reduced in the following reaction? PbS (s) + 4H 2 O 2 PbSO 4 (s) + 4H 2 O (l) Element that is oxidized: S Element that is reduced: O PROBLEM 4 Write the balanced formula, complete ionic, and net ionic equations for the following reaction: Al(OH) 3 (s) + HNO 3 Balanced formula equation: Al(OH) 3 (s) + 3HNO 3 Al(NO 3 ) 3 + 3H 2 O (l) Complete ionic equation: Al(OH) 3 (s) + 3H + + 3NO 3 Al NO 3 + 3H 2 O (l) Net ionic equation: Al(OH) 3 (s) + 3H + Al H 2 O (l) Page 4

5 PROBLEM 5 Using the half-reaction method, balance the following oxidation reduction reaction that occurs in basic solution. NO 2 + Al (s) NH 3 (g) + AlO 2 NO 2 NH 3 (g) Al (s) AlO 2 NO 2 NH 3 (g) + 2H 2 O (l) Al (s) + 2H 2 O (l) NO 2 + 7H + NH 3 (g) + 2H 2 O (l) Al (s) + 2H 2 O (l) AlO 2 AlO 2 + 4H + NO 2 + 7H + + 6e NH 3 (g) + 2H 2 O (l) Al (s) + 2H 2 O (l) AlO 2 + 4H + + 3e x1 x2 NO 2 + 7H + + 6e NH 3 (g) + 2H 2 O (l) 2Al (s) + 4H 2 O (l) 2AlO 2 + 8H + + 6e NO 2 + 7H + + 6e + 2Al (s) + 4H 2 O (l) NH 3 (g) + 2H 2 O (l) + 2AlO 2 + 8H + + 6e NO 2 + 2Al (s) + 2H 2 O (l) NH 3 (g) + 2AlO 2 + H + NO 2 + 2Al (s) + 2H 2 O (l) + OH NO 2 + 2Al (s) + 2H 2 O (l) + OH NH 3 (g) + 2AlO 2 + H + + OH NH 3 (g) + 2AlO 2 + H 2 O (l) NO 2 + 2Al (s) + H 2 O (l) + OH NH 3 (g) + 2AlO 2 NO 2 + 2Al (s) + H 2 O (l) + OH NH 3 (g) + 2AlO 2 Page 5

6 PROBLEM 6 (4 marks) The electron in a ground-state H atom absorbs a photon of wavelength nm. To what energy level does the electron move? E= B ( Z2 2 n final Z2 ) 2 n initial or H( 1 λ = R 1 2 n 1 in ) 2 n out λν = c and ΔE = hν 1/97.20 x 10 9 = x 10 7 (1 1/n 2 ) E = hc / λ n 2 = n = 4 E = x J x J = x (1/n 2 1) n 2 = n = 4 4 PROBLEM 7 Determine the wavelengths of an 85 kg person skiing at 50 km/hr. λ = h / mv = x / (85)(13.889) λ = x m 50 km/hr = m/s 5.6 x m Page 6

7 PROBLEM 8 (11 marks) Short-answer questions. (a) Rank the photons in terms of increasing energy: A. blue (λ = 453 nm); B. red (λ = 660 nm); C. yellow (λ = 595 nm). < < B C A (b) Indicate whether these electron transitions correspond to an absorption or an emission of energy: i. n = 2 to n = 4 absorption ii. n = 3 to n = 1 emission (c) Arrange the following H atom electron transitions in order of increasing frequency of the photon absorbed or emitted: A. n = 2 to n = 4; B. n = 2 to n = 5; C. n = 4 to n = 3. < < C A B (d) How many orbitals in an atom can have each of the following designations: i. 1s 1 iii. 3p z 1 ii. 4d 5 iv. n = 3 9 (e) What is the maximum number of electrons that can occupy each of the following subshells: i. 3p 6 iii. 2s 2 ii. 5d 10 iv. 2f 0 Page 7

8 (f) Write a full set of quantum numbers (n, l, m l, and m s )for the following: i. the outermost electron in an Rb atom 5, 0, 0, +½ ii. the electron gained when an S ion becomes an S 2 ion 3, 1, +1, ½ (g) Write the full ground-state electron configuration for each: i. Ag 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 4d 10 ii. S 1s 2 2s 2 2p 6 3s 2 3p 5 (h) How many core and valence electrons are present in an atom of each of the following elements? i. O Core: 2 Valence: 6 ii. Sn Core: 46 Valence: 4 (i) Each of the following electron configurations represents an atom in an excited state. Identify the element. i. 1s 2 2s 2 2p 6 3s 1 3p 1 Element: Mg ii. 1s 2 2s 2 2p 5 3s 1 Element: Ne Page 8