Question 1 (20 points): Calculate the pH change in a 1-L buffer solution of 0.10

Question

Question 1 (20 points): Calculate the pH change in a 1-L buffer solution of 0.100 M HC2H3O2 (acetic acid) and 0.100 M NaC2H3O2 (sodium acetate) when 0.010 mol of solid NaOH is added to the buffer. Question 2. (10 points) Phenylacetic acid (C6H5CH2COOH, simplified here as HPAc) builds up in the blood of people with phenylketonuria, an inherited disorder that, if untreated, causes mental retardation and death. A study of the acid shows that the pH of 0.12 M HPAc is 2.62. What is the Ka of phenylacetic acid? Question 3. (10 points). Dimethylamine, (CH3)2NH, a key intermediate in detergent manufacturing, has a Kb of 5.9 x 10-4. What is the pH of 1.5 M (CH3)2NH? Question 4 (10 points): Please follow the link for the article about the entrapment of a man in a sinking boat off the coast of Nigeria for 60 hours. (Please cite referenced works or tables) https://www.theguardian.com/world/2013/jun/12/nigeria-sailor-survive-air-pocket https://www.livescience.com/41688-how-to-survive-underwater-for-3-days.html a) Calculate the amount (volume) of O2 required for a healthy male adult to breathe for 60 hours at 1 atm. What is this volume at 30 m below sea level? b) Using the dimensions of the air pocket at 30 m below sea level, approximate the dimensions of the air bubble at sea level (1 atm). Question 5 (20 points): Locate a tube of toothpaste and answer the following questions (please cite referenced works or tables). a) Draw the chemical structure of the anticavity active ingredient(s). b) How many grams of fluoride ion are used to brush your teeth in an entire year, assuming that a healthy person brushes their teeth twice a day. How many fluoride atoms? Use drawings and pictures to support your answer. c) Using the MSDS LD50 on the amount of ingested fluoride, how much toothpaste (L) can you accidentally ingest in one sitting without causing death? Question 6 (10 points): Obtain a package of Alka-Seltzer, an antacid, or locate the label of ingredients from online or in your medicine cabinet. a) List the ingredients. b) Why does Alka-Seltzer foam and bubble when dissolved in water? Which ingredient is the antacid? c) Write the reaction responsible for the formation of bubbles, and the reaction responsible for the antacid activity. Question 7 (20 points): Look up the maximum concentrations set by the U.S. Environmental Protection Agency for lead and cadmium in drinking water. a) What are these concentrations in milligrams per liter? In moles/L? b) Based on your answer from part (a), which is more toxic? Explain briefly. c) How many liters of water contaminated at this maximum level must you drink to consume 1.0 g of lead? To consume 1.0 g of cadmium?

Explanation / Answer

1. pH change

initial pH = 4.75

after 0.01 M NaOH is added

final [CH3CO2H] = (0.1 M x 1 L - 0.010)/1 L = 0.09 M

final [CH3CO2Na] = (0.1 M x 1 L + 0.010)/1 L = 0.11 M

Using Hendersen-Hasselbalck equation,

pH = pKa + log(base/acid)

     = 4.75 + log(0.11/0.09) = 4.84

pH change = final - initial = 4.84 - 4.75 = 0.09

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2. phenylacetic acid HPAc

0.12 M solution has pH = 2.62

pH = -log[H+] = 2.62

[H+] = [PAc-] = 2.4 x 10^-3 M

Ka = [PAc-][H+]/[HPAc]

     = (2.4 x 10^-3)^2/(0.12 - 2.4 x 10^-3)

     = 4.9 x 10^-5

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3. Dimethyl amine pH

[(CH3)2NH] = 1.5 M

(CH3)2NH + H2O <==> (CH3)2NH2+ + OH-

let x amount has reacted

Kb = [(CH3)2NH+][OH-]/[(CH3)2NH]

with x being a small change

5.9 x 10^-4 = x^2/(1.5)

x = [OH-] = 0.03 M

[H+] = Kw/[OH-] = 1 x 10^-14/0.03 = 3.33 x 10^-13 M

pH = -log[H+] = 12.48     

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