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26 October 2009 Recitation

# 26 October 2009 Recitation - buffer Identify specifically...

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Recitation 26 October 2009 1. Rank the following in order of increasing acidity (same may be relatively equal). Group Problems NaBr, KNO 2 , HClO 4 , HNO 2 , NH 4 ClO 4 , and NH 4 NO 2 . 2. Calculate the pH of the following solutions: a. 0.1 M NaF (HF K a = 7.2 x 10 -4 ) b. 0.1 M NH 4 Cl (NH 3 K b = 1.8 x 10 -5 ) c. 0.1 M NH 4 C 2 H 3 O 2 (Ammonium Acetate) HC 2 H 3 O 2 K a = 1.8 x 10 -5 NH 3 , K b = 1.8 x 10 -5 3. Calculate the pH of a solution of: a. 0.1 M HF b. 0.1 M HF and 0.1 M NaF Explain using LeChatelier’s Principle why the pH is different for the two solutions above.

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4. What is meant by the capacity of a buffer? How do the following buffers differ in capacity? How do they differ in pH? a. 0.01 M acetic acid and 0.01 M sodium acetate b. 0.1 M acetic acid and 0.1 M sodium acetate c. 1.0 M acetic acid and 1.0 M sodium acetate 5. Calculate the pH of a solution formed by mixing 100.0 mL of 0.100 M NaF (HF, K a = 7.2 x 10 -4 ) and 100.0 mL of 0.025 M HCl. 6. Using the acetate buffer, outline the steps needed to prepare a 20.0 L solution of the
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Unformatted text preview: buffer. Identify specifically the number of moles needed to yield the desired pH of 5.1. (acetic acid and sodium acetate, K a = 1.8 x 10-5 for acetic acid) 7. How many moles of NaOH must be added to a 1.0 L solution of 2.0 M HC 2 H 3 O 2 (K a = 1.8 x 10-5 ) to produce a solution buffered at each of the following pH values? a. pH = pKa b. pH = 4.00 c. pH = 5.00 Individual Problems 1. Calculate the pH of a solution that is 0.60 M HF and 1.00 M HF. 2. What relative ratios of NH 4 Cl and NH 3 (K b = 1.8 x 10-5 ) are needed to achieve the following buffered pH values? a. 9.25 b. 9.61 c. 9.02 What is the working pH range for this buffer? 3. Using 1 L of the buffered solution in problem 1, calculate the pH observed after the following additions: a. 100 mL of 1.0 M HCl is added b. 100 mL of 1.0 M NaOH is added...
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26 October 2009 Recitation - buffer Identify specifically...

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