PRE-CLASS ASSIGNMENT BEFORE coming to class, you need to read this document L05 DOCU in its entirety. This includes both Lab 5A Molly Case Study, as well as Lab 5B on buffers and titration. At the beginning of class, you will need to take the quiz for Lab #5 and turn it in. To prepare for the quiz, you should be familiar with units on a log scale; Molly’s symptoms; Molly’s treatments (initially and after lab results—not why, just what); neutralization reactions; Henderson-Hasselbach equation; purpose of a buffer; which types of acids and bases can act as a buffer; and what a titration curve is. LAB 5A: MOLLY CASE STUDY THE CASE OF THE MORTIFIED MOM: ACIDS, pH AND BUFFERS BY TERRY PLATT, DEPT OF BIOLOGY, UNIVERSITY OF ROCHESTER MODIFIED BY BRENDA TEMPLE, DEPT OF BIOCHEMISTRY, UNC-CH Part I—Evening at the Mathews Sarah Mathews, an accountant, is sitting with her husband Tom having their after- dinner coffee, and asks, "Another cup, honey?" "No thanks; more than one seems to bother me these days, especially this late in the evening." Sarah is about to express her concern when their son Paul, a high school junior, bursts in and says, "Mom and Dad! Do you know what the pH is of that coffee you're drinking?" "What's pH?" asks Tom. “C’mon Dad, it’s a measure of acidity—and coffee is like a pH of 5!” Sarah responds, “But I thought that neutral solutions, like plain water, are pH 7, which doesn’t seem like very far away from 5 to me …” “Yeah, right, Mom; pH 5 is only 100-times more acidic than water. Or try that vinegar we put in our homemade salad dressing—it’s around pH 3, 100 times more acidic than this coffee is!” His dad asks, “I don’t get it. How can only two units, like the difference between 3 and 5, or 5 and 7, give you 100 times as much?” “Cause, Dad, it’s a log scale—you know, like earthquakes—and the 2 units mean 2 powers of 10, like 10-squared; that where the 100 comes from!” Sarah chimes in, “So you mean if there were 3 pH units difference, that would be 10 cubed, or 1000 times? And if you went from pH 3.7 to pH 6.7, that would also be 1000-fold?” “Now you’re getting it! “Whoa, slow down, Paul,” replies Tom, “you’ve got my head spinning now. Besides, its getting late and you have school tomorrow, so off to bed with you!” Part II—The Next Day The next day brought a beautiful fall afternoon, and the maples were just starting to show their autumn colors. Sarah was enjoying her long late afternoon run and was only a few blocks away from home when she was surprised by the ringtone of her phone. “Mom, its Paul! Get home quick! Molly, even though she’s only 3, she must have managed to climb onto the toilet seat, then the sink, and reach up to the medicine cabinet. She must have thought the pills in there were candy, and I think she started eating a whole bunch of aspirin tablets and then she fell! I finally heard her crying, and went upstairs where I found her curled up and whimpering on the bathroom floor, with colored pills and cracked bottles scattered around. I don’t think she broke anything, but it
You've reached the end of your free preview.
Want to read all 8 pages?
- Spring '13
- pH, buffer solution