20L_StudyGuide - Chemistry 20L Study Guide for Exam #2...

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Chemistry 20L Study Guide for Exam #2 Winter 2010 Cumulative Exam #2 (IN CLASS) – Tuesday (March 9 th ) at 10am in CS76 You have a MAXIMUM of 50 minutes to complete the exam. Don't be late. NO EXTRA TIME will be given if you are late and there will be NO MAKE UP EXAMS. The Final exam is a CLOSED book and CLOSED notes exam. Make sure you also bring a pen, a CALCULATOR (CHECK THE BATTERIES!) and your student ID to the exam. Extra Office Hour: Monday (March 8 th ) 12 – 1 pm in 2070B YH Exam #2 will be comprehensive (it may include ANY of the experiments and topics/concepts that covered in lectures). There is NO RE-GRADE OR MAKE UP on EXAM #2. Please note that the questions on this study guide do NOT necessary reflect the “style” of the questions you will see on the actual exam. Focus on the concepts when working on the following questions. Keep in mind that a question can be written in many different ways that relates to the same concept(s). (I) Acid-Base Equilibrium and Buffer Chemistry Make sure you always check any assumption that you make during the calculations. (1) Which of the following molecules are acids and which ones of them are bases? HNO 3 , CH 3 COOH, NH 4 Cl, H 2 CO 3 , C 6 H 5 NH 2 (2) Write the chemical reaction with base (OH - ) for the molecules that you identified as acids in question #1. Write the formula of the conjugate bases for these molecules. (3) Write the chemical reaction with acid (H + ) for the molecules that you identified as bases in question #1. Write the formula of the conjugate acids for these molecules. (4) (a) Explain why the equivalence point pH=7 for a strong acid and strong base titration? (b) Explain why the equivalence point pH >7 for a weak acid and strong base titration? (You should explain this question by showing the relevant chemical reactions) (5) What volume of 0.250 M NaOH is required to reach the equivalence point with 18.49 mL of 0.200 M H 2 SO 4 ? (For simplicity, you may assume the 2 protons dissociate completely in H 2 SO 4 ) (6) What volume of 0.500N NaOH is required to titrate with 100.0ml of 0.120 N of H 2 SO 4 to the equivalence point? (7) Calculate the [H + ], pH, [OH - ] and pOH in 0.030 M HCl. (8) What is color of the bromocresol green indicator in the following solutions? (a) 0.05 M HCl (b) 1.2X10 -4 M HCl (c) 250 ppm HCl Color Range of Bromocresol Green: pH= 0 - 3.8 yellow; pH=3.8 - 5.4 green; pH greater than 5.4 blue (9) Suppose you have a 100.00ml of 0.01000M methylamine (CH 3 NH 2 ) solution ( K b = 4.4 X 10 -4 ). (a) Calculate the pH of this solution. (b) What is the equivalence point pH for the titration of 0.01000M HCl with methylamine?
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(10) Calculate the pH of the solution by mixing 50.00 mL of 0.2000 N NH 3 (K b = 1.8 X10 -5 ) with 10.00 mL of 0.1000 N HCl. (11)
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This note was uploaded on 09/03/2010 for the course CHEM 20A C 142140249 taught by Professor Scerri during the Winter '09 term at UCLA.

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20L_StudyGuide - Chemistry 20L Study Guide for Exam #2...

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