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tutorial 4a solutions (test 1 review)

# tutorial 4a solutions (test 1 review) - CHEM 1E03...

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CHEM 1E03 TUTORIAL #4a Solutions _____________________________________________________________________ Version 1 Page 1 1. Cl 2 (g) reacts with a solution of KI(aq) by oxidizing iodide ions into iodine, I 2 (aq). What volume of chlorine gas (in mL) , measured at 25.00°C and 1.00 atm, is needed to completely react with 25.0 mL of 0.200 M KI(aq)? A) 61.2 B) 122 C) 15.2 D) 30.6 E) 6.12 The balanced reaction is Cl 2 + 2 KI 2 KCl + I 2 25.0 mL of 0.200 M KI(aq) contains 5 10 -3 mole KI which requires 2.5 10 -3 mole Cl 2 PV = nRT V = nRT/P = 2.5 10 -3 x 0.08206 x 298.15 /1 = 0.0612 L = 61.2 mL 2. How many grams of magnesium oxide, MgO , can be produced from 3.50 g of magnesium metal and 1.60 g of oxygen gas? The balanced reaction is: Mg + ½ O 2 MgO 1.6 g O 2 (g) = 0.05 mole O 2 and 3.50 g Mg = 0.144 mole Mg. Hence O 2 is the limiting reagent. 0.05 mole O 2 yields 0.1 mole MgO, i.e. 4.03 g. 3. A sample of a barium salt weighing 0.676 g was completely dissolved in water and treated with an excess of sodium sulfate. A precipitate formed which was dried and weighed, yielding 0.4105 g. What is the mass percentage of barium in the original salt sample? The precipitation reaction is Ba salt(aq) + Na 2 SO 4 BaSO 4 (s) + Na salt (aq) mass (BaSO 4 ) = 0.4105 g 0.4105/233.40 = 1.76 10 -3 mole BaSO 4 = 1.76 10 -3 mole Ba 2+ 1.76 10 -3 mole Ba 2+ = 0.2415 g Ba 0.2415 g (Ba)/0.676 g (sample) = 0.357 = 35.7%

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CHEM 1E03 TUTORIAL #4a Solutions _____________________________________________________________________ Version 1 Page 2 4. Aqueous chromate ions, CrO 4 2– (aq), react with zinc metal in acidic solution to produce Cr 3+ (aq) and Zn 2+ (aq) ions. When the reaction is balanced with the smallest possible integers as stoichiometric coefficients, what is the coefficient for H 2 O ? Balanced reaction: 16 H + + 2 CrO 4 2- + 3 Zn 8 H 2 O + 2 Cr 3+ + 3 Zn 2+
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