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Lecture Comments (17)

0 answers

Post by Shane Lynch on March 25, 2014

Why is this taking so long to buffer. I want to skip to stoichiometry but it won't load.  

0 answers

Post by Yisrael Harris on May 20, 2013

If a compound has a molar mass of x g/mol, then the mass of one molecule of that compound is x amu, correct? Why then was the concept of molar mass invented, instead of simply stating molecular mass in amu, which seems more intuitive and simpler to me?

1 answer

Last reply by: Zachary McCoy
Fri Jan 3, 2014 10:47 PM

Post by Yisrael Harris on May 19, 2013

Is there a way to report 704.969 to two significant figures *not* using scientific notation?

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Post by Yisrael Harris on May 19, 2013

A bit of talking in the background. Distracting.

1 answer

Last reply by: Zachary McCoy
Fri Jan 3, 2014 10:44 PM

Post by Yisrael Harris on May 19, 2013

When I was in high school, we were taught a term "significant digits". Is this term synonymous with "significant figures"?

1 answer

Last reply by: Velmurugan Gurusamy
Wed Sep 25, 2013 7:42 AM

Post by Andrew Claes on February 25, 2013

I have another question about sigfigs, just to be sure...
If you have for example 36,889 as your arithmetic answer, but you have to work with only 4 sig.figs, is the scientific answer 36,88 or do you round off the number, rendering 36,89. thank you.

1 answer

Last reply by: Zachary McCoy
Fri Jan 3, 2014 10:44 PM

Post by Andrew Claes on February 25, 2013

Why does the molar mass of cholesterol have 5 significant numbers? the given masses only have 4 throughout the examples in this lecture. I was also unable to find the same answer even with C27H46O, which gives me 386,638 g/mol, or should I say 386,6 g/mol.

1 answer

Last reply by: Lisa Lim
Sun Nov 4, 2012 3:49 PM

Post by Bryan Grezeszak on May 31, 2012

Professor says cholesterol is C27H45O, and that's a molar mass of 386.67 g/mol. I calculated the molar mass according to that formula to be 385.6 g/mol.

So I figured something was wrong and I looked it up and the internet says cholesterol is C27H46O (46 H instead of 45 H), and that the molar mass is 386.65 g/mol, when I calculate I get a similar answer for that formula.

My question is: is there C27H45O cholesterol and the prof just accidentally gave the molar mass of the H46 version, or is all cholesterol H46 and he just made a mistake by writing 45, or am I just wrong completely on everything (if so please explain so that I get what happened!)

0 answers

Post by rachel brower on October 13, 2011

I love his lectures! His teaching abilities are far beyond any Chem professor I have ever had.

2 answers

Last reply by: Eun Jee Kang
Mon May 7, 2012 1:26 AM

Post by Ryan DiGiovanni on September 21, 2011

Is his math correct for the volume? I keep getting 204 cm3. Somebody help me here.

Significant Figures and the Mole

  • Master rules for significant figures: leading and trailing zeroes; use of scientific notation a x10 to a positive or negative power

  • The mole: Avogadro’s number of a specified entity (atom, molecule, electron etc.)

  • Molar masses: just add up the amus and put g (grams) at the end.

  • Practice interconversions between masses and numbers of moles

Significant Figures and the Mole

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Significant Figures: Sphere 0:14
  • Example: Cube 7:11
    • Example: Weight
  • The Mole 13:36
    • Examples: Number of Entities
    • Avogadro's Number
    • Carbon 12
    • Mass of 1 Mol
    • Molar Mass of Oxygen
  • Stoichiometry 25:15
    • Example: Molar Masses
  • Molar Mass 26:39
    • Example: Cholesterol
    • Example: Insulin
  • Additional Example 1
  • Additional Example 2