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Title: Started: Submitted: Time spent: Chapter 19(1) November 8, 2009 5:18 PM November 8, 2009 6:43 PM 01:24:48 Total score adjusted by 0.0 Maximum possible score: 12
Total score: 5/12 = 41.67% 1. Buffer Synthesis 1
Match the acid/base pair that is suitable for preparing a buffer of each given approximate pH. You will need to refer to Tables in the book of weak acids and bases and polyprotic acid
HCOOH/NaHCOO NaH2PO3/Na2HPO3 HOBr/NaOBr
9 4 7
Statement HCOOH/NaHCOO NaH2PO3/Na2HPO3 HOBr/NaOBr Score: 0/1
Response 4 9 7
Value Correct
Correct Match 4
Incorrect 7 Incorrect 9
2.
Indicator 5 Which indicator would be the best to use for a titration between 0.10 M HF with 0.10 M NaOH? You will probably need to consult the appropriate table in the book.
Student Response
Value
Correct Answer
Feedback
1. thymol blue, 100% color change at pH 8-10 2. bromothymol 0% blue, color change at pH 6-8 3. methyl red, 0% color change at pH 3-5 4. alizarin 0% yellow R, color change at pH 10-12
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5. methyl 0% violet, , color change at pH 0-2 Score: 0/1
3.
Chapter 11 Simple Buffer 16 Calculate the pH of a solution that is 0.079 M NH3 and 0.058 M NH4Cl. Kb of NH3 is 1.8 x 10-5.
Student Response Answer 2.12 Score: 0/1
Value 0%
Correct Answer 9.39
4.
Chapter 11 Moderate Buffer 6 The pH of 0.5 M formic acic, HCOOH, is 2.02. Calculate the difference in pH when 6.38 g of HCOONa is added to 338.1 mL of 0.50 M formic acid. Ignore any changes in volume. The Ka value for HCOOH is 1.8 x 10-4.
Student Response Answer 1.37 Score: 0/1
Value 0%
Correct Answer 1.47
5.
Buffer Ratio 2 What is the buffer component ratio, ([NO2-]/[HNO2]) of a nitrite buffer that has a pH of 2.52. Ka of HNO2 is 7.1 x 10-4.
Student Response Answer .235 Score: 1/1
Value 100%
Correct Answer 0.23
6.
Additions to Buffer 1 A buffer that contains 0.380 M of acid, HA 0.453 and M of its conjugate base A-, has a pH of 4.20. What is the pH after 0.0297 mol of NaOH are added to 0.708 L of the solution?
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Student Response Answer 4.45 Score: 0/1
Value 0%
Correct Answer 4.29
7.
Chapter 11 Titrations SS 8 Calculate the pH during the titration of 24.8 mL of 0.425 M NaOH with 0.111 M HCl after 12.8 mL of the acid have been added.
Student Response Answer 13.4 Score: 1/1
Value 100%
Correct Answer 13.38
8.
Chapter 11 Titrations WS 23 Calculate the pH during the titration of 20.00 mL of 0.1000 M CH3COOH(aq) with 0.1000 M NaOH(aq) after 20.41 mL of the base have been added. Ka of acetic acid = 1.8 x 10-5.
Student Response Answer 11 Score: 1/1
Value 100%
Correct Answer 11.01
9.
Chapter 11 Titrations SW 7 Calculate the pH during the titration of 20.00 mL of 0.1000 M trimethylamine, (CH3)3N(aq), with 0.1000 M HCl(aq) after 19.86 mL of the acid have been added. Kb of trimethylamine = 6.5 x 10-5.
Student Response Answer 10.5 Score: 0/1
Value 0%
Correct Answer 7.66
10. Chapter 11 Titrations EP SS 2 What is the volume in mL of 0.175 M NaOH(aq) needed to reach the equivalence (stoichiometric) point in the titration of 54.6 mL of 0.557 M HCl(aq).
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Student Response Answer 174 Score: 1/1
Value 100%
Correct Answer 173.8
11. Chapter 11 Titrations EPP SW 2 Determine the pH at the equivalence (stoichiometric) point in the titration of 44.9 mL of 0.208 M CH3NH2 by 0.426 M HNO3. The Kb of CH3NH2 is 3.6 x 10-4.
Student Response Answer 2.22 Score: 0/1
Value 0%
Correct Answer 5.71
12. Chapter 11 Titrations HEP SW 3 What is the volume in mL of 0.519 M HCl(aq) needed to reach halfway to the equivalence (stoichiometric) point in the titration of 37.7 mL of 0.786 M methylamine (Kb = 3.6 x 10-4).
Student Response Answer 28.5 Score: 1/1
Value 100%
Correct Answer 28.5
Done
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