# Answer Key_Exam 1 - Version 130 – Exam 1 – rowland...

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Unformatted text preview: Version 130 – Exam 1 – rowland – (53210) 1 This print-out should have 28 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points How many grams of Ca are contained in 113 mL of 0.52 M Ca(OH) 2 solution? 1. 1.18 g 2. 4.71 g 3. 8.71 g 4. 0.0588 g 5. 2.36 g correct Explanation: V Ca(OH) 2 = 113 mL [Ca(OH) 2 ] = 0.52 M ? g Ca = 0 . 113 L × . 52 mol Ca(OH) 2 L soln × 1 mol Ca 1 mol Ca(OH) 2 × 40 . 08 g Ca 1 mol Ca = 2 . 36 g Ca 002 10.0 points The vapor pressure of pure acetone (CH 3 COCH 3 ) at 30 o C is 240 torr. The va- por pressure of pure water (H 2 O) at 30 o C is 40 torr. If the total vapor pressure of a mix- ture of water and acetone at 30 o C is 190 torr, what is the mol fraction of acetone? 1. 0.75 correct 2. 0.25 3. 0.8 4. 0.2 Explanation: χ water + χ acetone = 1 χ acetone = x , χ water = 1- x P = P o water · χ water + P o acetone · χ acetone 190 torr = 40 torr · (1- x) + 240 torr · x x = 0 . 75 003 10.0 points Which one of the following is a water-soluble, weak electrolyte? 1. NH 4 ClO 2. KBr 3. Ca(OH) 2 4. H 2 CO 3 correct 5. H 2 SO 4 Explanation: All of the choices are electrolytes, but only carbonic acid (H 2 CO 3 , a weak acid) does not ionize completely, so it is a weak electrolyte. 004 10.0 points Which of the following statements about col- ligative properties of aqueous solutions is FALSE? 1. Osmosis is a colligative property. 2. The higher the concentration of solute in the solution, the higher the vapor pressure of the solvent. correct 3. Colligative properties only depend on the number of solute particles present in solu- tion. 4. For a given solution, the freezing point will be lowered more than the boiling point will be raised. Explanation: Colligative properties, which include osmo- sis, vapor pressure lowering, melting and boil- ing point elevations, depend only on the num- ber of solute particles present in solution, not on their properties. The effect on the melt- ing point of a given solution is more than the effect on its boiling point. With a higher concentration of non-volatile Version 130 – Exam 1 – rowland – (53210) 2 solute the concentration of the solvent in the solution is lower, causing the vapor pressure of the solution to be lower. 005 10.0 points Which of the following pairs have a van’t Hoff i factor of 3? 1. glucose and sodium chloride 2. calcium chloride and potassium sulfate correct 3. perchloric acid and barium hydroxide 4. magnesium sulfate and ethylene glycol 5. sodium sulfate and potassium chloride Explanation: 006 10.0 points The freezing point of seawater is about- 1.85 ◦ C. If seawater is an aqueous solution of sodium chloride, calculate the molality of seawater. The k f for water is 1.86 K/ m ....
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Answer Key_Exam 1 - Version 130 – Exam 1 – rowland...

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