ExamII - SOLUTION KEY TO PRACTICE EXAM II / CHAPTERS 4...

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Part I. Multiple Choice (100 Points Total) # 01. (5 pts) To which category does the following reaction belong? PbSO 4 (aq) + K 2 O(s) PbO(s) + K 2 SO 4 (aq) a. a gas-forming reaction b. an acid-base reaction c. a precipitation reaction answer d. an oxidation-reduction reaction e. none of the above # 02. (5 pts) Determine the oxidation number of chromium in H 2 CrO 4 . You may want to may use of the oxidation number table on page 8. a. Cr + b. Cr 2+ c. Cr 3+ d. Cr 4+ e. Cr 6+ answer Solution: H = +1; O = -2; Cr = x 2(+1) + x + 4(-2) = 0 2 + x – 8 = 0 x – 6 = 0 x = 6 ( i.e. Cr 6+ ) # 03. (5 pts) Which one of the following is a weak acid? a. HCl b. HNO 3 c. H 2 SO 4 d. HBr e. Acetic acid (C 2 H 4 O 2 ) answer (all others are strong acids) # 04. (5 pts) Oxidation-reduction reactions always involve ____________ . a. the transfer of electrons b. an oxidizing agent c. a reducing agent d. a precipitate CHEM 1311/TAMUCC/J. M. Southard, PhD 1
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e. a , b & c answer # 05. (5 pts) Balance the acid-base reaction with the smallest whole number coefficients . I’ve placed blanks in front of each compound for your convenience. Choose the answer that is the sum of the coefficients in the balanced equation. Do not forget coefficients of “one”. 3 Ca(OH) 2 + 2 H 3 PO 4 (aq) 1 Ca 3 (PO 4 ) 2 (aq) + 6 H 2 O( l ) a. 4 b. 5 c. 8 d. 9 e. 12 answer (b/c 3 + 2 + 1 + 6 = 12) # 06. (5 pts) Based on the following balanced equation determine how many moles of O 2 are required to react with 23.5 moles of CH 3 OH? 2 CH 3 OH( l ) + 3 O 2 (g) 2 CO 2 (g) + 4 H 2 O(g) a. 47.0 b. 35.3 answer c. 11.8 d. 40.0 e. 23.5 Solution: 2 O mol 3 . 35 OH 3 CH mol 2 2 O mol 3 OH 3 CH mol 5 . 23 × # 07. (5 pts) Based on the following balanced equation determine how many moles of H 2 can be produced from 72.9 g Mg and an excess of HCl. 2 HCl(g) + Mg(s) MgCl 2 (s) + H 2 (g) a. 4.50 mol b. 3.00 mol answer c. 1.50 mol d. 9.00 mol e. 6.00 mol Solution: 2 H mol 00 . 3 Mg mol 1 2 H mol 1 Mg g 31 . 24 Mg mol 1 Mg g 9 . 72 × × # 08. (5 pts) What is the identity of the “oxidizing agent” in the following oxidation-reduction reaction? 2 Mg(s) + S 2 (g) 2 MgS(s) a. Mg is “reducing agent b/c Mgº Mg 2+ ) CHEM 1311/TAMUCC/J. M. Southard, PhD 2
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b. S 2 answer (is “oxidizing agent” b/c Sº S 2- ) c. MgS d. This reaction does not involve electron-transfer e. None of the above # 09. (5 pts) Based on the following balanced equation, what mass of SiF
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