Chem 1121 - Robertson

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Re: Chem 1121 - Robertson

Postby Ron Robertson » Wed Mar 25, 2015 4:49 pm

The quiz is a little long in the morning but it is worth 24 pts (4 bonus pts). You know that there will be a stoichiometry type question and a redox question where you have to assign ox numbers for the alum experiment. For the pH lab, do the prelab! Make sure you know how to use the dilution equation and then how to find the concentrations of all ions for a strong or weak acid. Finally take those concentrations and find the pH of the solution. There will be no questions about the acidity of salt solutions on the quiz.

The lab is due at 5 pm on Friday with page 7 of 9, a revised calculation page, and post lab question #1.
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Ron Robertson » Thu Mar 26, 2015 6:15 am

I was wondering if any of your lecture instructors taught the sf rules for pH calculations. I just received an email from Dr. Sullivan indicating that she had gone over it. I have copied a part of her email below where she summarizes what she has taught.

Sig Fig Rules for pH:
(1) Additional rules are needed because pH is a log based calculation.
(2) The number of sig figs in the concentration determines the number of digits beyond the decimal in the pH.

R2 - This means that if you have an H+ concentration of 2.5 x 10-4, then your pH would be 3.60. I can explain further for those interested. Also in our lab today, you have to convert pH to concentration so what would this mean? A pH of 3.60 would be a concentration of 2.5 x 10-4.

See you soon. . .
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Ron Robertson » Mon Mar 30, 2015 10:11 am

I have graded your quizzes and labsheets and they are ready for pick-up. An answer key is posted for the quiz.

I will try on Thursday to briefly address 2 real weaknesses shown on the quiz: (1) assigning ox # and (2) working stoichiometry problems. Please feel free to drop by and ask for help.
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Ron Robertson » Wed Apr 01, 2015 9:41 am

Answers to pre-lab on Buffer Experiment

1. NH4+/NH3

2. pair with a Ka of 1.82 x 10-4

3. 4.86

Make sure you understand the reasons for these answers. The Henderson-Hasselbalch equation is big on this lab. Lots of calculations. Come with your thinking caps on! Lots of applications to living systems.
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Ron Robertson » Thu Apr 02, 2015 7:46 am

Buffer lab - Due at 5 pm Monday

Page 3 of 5 with Post lab #1 question
Revised Calculation Pages

The lab is deceptively simple experimentally and devilishly difficult in the theoretical calculations. We will do the lab and return to E306 to work on the calculations, guided by the revised calculation pages.
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Ron Robertson » Thu Apr 02, 2015 2:58 pm

Your quizzes are graded and ready for pickup. A key is posted. Many of you don't understand this material. It's not easy for sure but oh so important. Please come by and let's try to make some improvement in your understanding!
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Ron Robertson » Tue Apr 07, 2015 9:21 am

Lab sheets are graded and ready for pickup. Are you ready for the quiz tomorrow?
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Jordanelise Harris » Tue Apr 07, 2015 11:40 am

Sir , tomorrow is wednesday
Jordanelise Harris
 
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Re: Chem 1121 - Robertson

Postby Ron Robertson » Tue Apr 07, 2015 2:24 pm

Right you are -- I must have been thinking about the quiz in my 1111 lab this morning. Sometimes you folks seem to run together.

I do appreciate that you are reading the message board . . . .and so. . . Are you getting ready for the quiz on Thursday?
Ron Robertson
 
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Re: Chem 1121 - Robertson

Postby Jordanelise Harris » Tue Apr 07, 2015 9:29 pm

I look at it religiously. Yes sir.
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