16 Structure and Acid Strength

# 16 Structure and Acid Strength - What is the Ka value for a...

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1 1 What is the K a value for a weak acid if a 0.01 M solution has a pH of 3.0? A) 9.9 x 10 –5 B) 1.0 x 10 –4 C) 1.1 x 10 –4 D) 1.0 x 10 –6 1)Write the acid ionization reaction equation. 2) Construct the RICE table. 3) Write the K a expression. 4) Evaluate the amount that reacts from the pH. 5) Plug in the values and calculate K a . 2 What is the K a value for a weak acid if a 0.010 M solution has a pH of 3.0? x x 0.010M–x E +x +x -x C 0 0 0.010 M I + A H 3 O + HA + H 2 O R x = 1 x 10 3 from pH info K a = (1.0x10 3 ) 2 / (0.010 – 0.001) K a = 1.1 x 10 4

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2 3 Calculate the pH of a 0.25 M solution of NH 3 given pK b = 4.745. Plan Construct the RICE table. Write the K b expression. Use K b to calculate [OH - ]. Calculate the pOH from [OH - ]. Calculate pH from the pOH. Possible Answers A) 2.67 B) 11.3 C) 3.45 D) 10.8 4 Solution .25 M 0 0 -x x x .25-x x x   4 3 2 4.745 3 10 0.25 2.12x10 [ ] 2.67 14 2.67 11.3 b NH OH K NH x x x OH pOH pH     Assume 0.25-x ~ 0.25 Remember what x is!
3 5 Special Part 2 Review for Exam 2 Thursday Evening, March 10, 7:30 PM Chemistry Learning Center Chemistry Bldg Room 312 Work pertinent problems, engage with conceptual questions, & obtain a review worksheet.

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16 Structure and Acid Strength - What is the Ka value for a...

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