103AaExam2Key - Exam 2A Grader Key l. (4) A 455 g sample of...

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Unformatted text preview: Exam 2A Grader Key l. (4) A 455 g sample of aluminum at 280° C absorbs heat until its temperature is 97.5 °C. How many joules of heat did the aluminum absorb? The specific heat of aluminum is 0.902 J/g °C. 4,4, = (455g)(0.902J/ g°C)(97,5 _ 2&0) z. 2.85 X104J Partial Credit: 3 points if set up is correct. -1 if sig figs or units are wrong. 2. (5) Fill in the blanks in the name-formula table below: Barium “ 3 OK Hem Diphosphorus P2134 tetrafluoride Chem 103A Examination 11 June 23, 2003 Page 2 3. (12) Balance the equations below: (a) Combustion of the hydrocarbon C14H20 [M C14H20 + 1902 -—> 14C02 + 10H20 4. (12) Write a balanced equation for the reaction (if any) for each of the following ionic compound pairs in aqueous solution. Then write their balanced net ionic equations. (a) NaF and Ca (CH3COO)2 (Can is insoluble) , 2 Na+(aq) + 2 F“(aq) + Ca+2(aq) + 2 CH3CO§(3¢D —> CaF2(s) + 2 Na+(aq) + 2 CH3CO§(aq) Ca+2(aq) + 2-F‘(aq) ————> CaF2(s) (b) (NH4)ZS and FeC12 (FeS is insoluble) 2 NH:(aq) + sz’(aq) + Fe2+(aq) + 2Cr(aq) -> FeS(s) + 2 NH;(aq) + 2 C1‘(aq) Fez+(aq) + Sz’(aq) ---> FeS(s) / W 7 77/, 5. (8) Write a balanced equation for the reaction of phosphoric acid, H3PO4, with sodium hydroxide, NaOH. H3PO4(aq) + 3 NaOH(aq) —> N33P04(aq) + 3 H20“) \ ; \“\\‘ ) Chem 103A Examination 11 June 23, 2003 Page 3 6. (10) Determine the oxidation number for each atom in this equation: Sb283(s) + 3Fe(s) ——’ 3FeS(s) + 2Sb(s) Cite the oxidation number rule(s) you used to choose your answers. The oxidation numbers of Fe and Sb are 0 (Rule 1). The oxidation numbers in szS3 are +3 for Sb5+ and -2 for 52“ (Rules 2 and 4); the oxidation numbers in FeS are +2 for Fe“ and —2 for 52— (Rules 2 and 4). 7. (10) Which are the oxidizing and reducing agents, and which atoms are oxidized and reduced in the following reaction? Explain. PbO(s) + CO(g) —’ Pb(s) + C02(g) In the reaction Pb0(s) + CO(g) —> Pb(s) + C02(g), Pb2+ is reduced to Pb; Pb2+ is the oxidizing agent. C2+ is oxi- dized to C“; C2+ is the reducing agent. Chem 103A Examination ll 6 (9) This problem deals with a water solution of iron(lll) chloride. Three points each Partial Credit: 2 points if set up is correct. -1 if Sig figs or units are wrong. (a) How many moles of ironall) chloride are in a 55.0 mL sample of this solution? 1L x 0.157m01 lOOOmL 1L (b) How many grams of iron(lH) chloride are in a 197 mL sample of this solution? 1L 0.157mol 162.21g x x————-— 55.0mL x = 0.00864mol l97mLx———— —— =5.02g lOOOmL 1L lmol (c) What is the concentration of chloride ion (in mol/L) in this solution? . 7 F l 3 l ' 015 mol 6C3 m0 Cl :0-471m01/L X —-—— 1L lmolFeCl3 Chem 103A Examination 1] 7 (9) This problem involves using the balanced equation (shown below)... Three points each Partial Credit: 2 points if set up is correct. —1 if sig figs or' units are wrong. (a) How many moles of carbon dioxide can be formed fi'om 17.0 g of calcium carbonate? lmol lmolCO2 17.0g x ———x —————— 100.09g lmolCaCO3 = 0.170mol (b) How many grams of calcium oxide can be formed from 75.0 g of calcium carbonate? Molecular wt. CaO: 40.08 + 16.00 = 56.08 lmolCaCO3 lmolCaO X 56.08gCa0 75.0 g x x ‘— *— 100.09g lmolCaCO3 lmolCaO = 42.0g (0) What total weight of carbon dioxide plus calcium oxide can be fbrmed from 2.00 mol of calcium carbonate? 2.00x 100.09 g/mol = 200. g (3 Sig figs) ...
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This note was uploaded on 10/21/2009 for the course CHEM 103 taught by Professor Keller during the Spring '07 term at University of Arizona- Tucson.

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103AaExam2Key - Exam 2A Grader Key l. (4) A 455 g sample of...

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