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Spring 09 Recitation Quiz 1

Spring 09 Recitation Quiz 1 - CHEM 0120 Golde SPRING 2009...

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CHEM 0120 SPRING 2009 Monday 1:00 PM Golde QUIZ 1 WEEK 2 January 12, 2009 Name_______________________________ Show your work or give your reasoning in each question. 1. (a) Write the full (molecular) equation and the net ionic equation for the acid-base (double- displacement) reaction of HNO 3 (aq) with KOH(aq). (b) Prove that all strong acid-strong base reactions have the same net ionic equation. (c) (If necessary), rewrite your net ionic equation in the form of a Bronsted-Lowry reaction 2. What volume of 0.316M Na 2 SO 4 solution contains 4.08 x 10 -3 mol of Na 2 SO 4 ? ANSWERS 1. (a) HNO 3 (aq) + KOH(aq) KNO 3 (aq) + H 2 O(l) H + (aq) + OH - (aq) H 2 O(l) (b) All strong acids ionize to produce H + and a spectator ion; all strong bases dissociate to give OH - and a spectator ion. (c) For a Bronsted-Lowry equation, we must replace H + by H 3 O + , i.e. H 3 O + (aq) + OH - (aq) H 2 O(l) + H 2 O(l) 2. Volume = 4.08 x 10 -3 mol Na 2 SO 4 x 2 4 1 L 1000 mL x 0.316 mol Na SO 1 L = 12.9 mL CHEM 0120 SPRING 2009 Monday 6:00 PM Golde QUIZ 1 WEEK 2 January 12, 2009 For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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Name_______________________________ Show your work or give your reasoning in each question. 1. Consider the Bronsted-Lowry reaction: N 2 H 5 + (aq) + OH - (aq) N 2 H 4 (aq) + H 2 O(l) (a) For this reaction, assign each species as a Bronsted-Lowry acid or base. (b) For this reaction, identify the two conjugate acid-base pairs. (c) Draw Lewis structures of N 2 H 5 + and N 2 H 4 . For the base , circle a lone pair of electrons which is basic; for the acid , circle a H atom which is acidic. 2. 10.0mL of 0.250M CaCl 2 were mixed with 20.0mL of 0.500M NaCl solution. Determine the molar concentration of Ca 2+ ions in the resulting solution. ANSWERS 1. (a,b) N 2 H 5 + loses a H + to form N 2 H 4 in this reaction. Hence N 2 H 5 + is an acid and N 2 H 4 is its conjugate base. OH - gains a H + to form H 2 O. Hence OH - is a base and H 2 O is its conjugate acid. H N N H H H H H N N H H H (+) (c) Base, N 2 H 4 : circle either lone pair; acid: circle any H on the right-hand N atom. 2. We focus on the dilution of 10.0 mL of CaCl 2 by the addition of 20.0 mL of the other solution to form a final solution of volume 30.0 mL.
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