Homework 02

# Homework 02 - Su Yung Homework 2 Due midnight Inst...

This preview shows pages 1–3. Sign up to view the full content.

Su, Yung – Homework 2 – Due: Sep 19 2007, midnight – Inst: FAKHREDDINE 1 This print-out should have 48 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Each question is worth 1 point. 001 (part 1 of 1) 1 points Calculate the number of carbon atoms in 4.56 grams of ethanol (CH 3 CH 2 OH). 1. 1 . 79 × 10 23 atoms 2. 5 . 97 × 10 22 atoms 3. 1 . 19 × 10 23 atoms correct 4. 5 . 49 × 10 24 atoms 5. 2 . 53 × 10 26 atoms Explanation: m CH 3 CH 2 OH = 4.56 g Each CH 3 CH 2 OH molecule contains two carbon atoms. There are Avogadro’s number of ethanol molecules in one mole of ethanol. We need the molecular mass of ethanol so we can convert grams of ethanol to moles ethanol: Molecular mass of CH 3 CH 2 OH = 2(12 . 01 g / mol) + 6(1 . 01 g / mol) +1(16 . 00 g / mol) = 46 . 08 g / mol We can use this molecular mass to convert g ethanol to mol ethanol: ? mol ethanol = 4 . 56 g CH 3 CH 2 OH × 1 mol CH 3 CH 2 OH 46 . 08 g CH 3 CH 2 OH = 0 . 09896 mol CH 3 CH 2 OH We can now use Avogadro’s number and the ratio of C atoms to CH 3 CH 2 OH molecules to find the number of carbon atoms: ? atoms C = 0 . 09896 mol CH 3 CH 2 OH × 6 . 022 × 10 23 molec CH 3 CH 2 OH 1 mol CH 3 CH 2 OH × 2 atoms C 1 molec CH 3 CH 2 OH = 1 . 192 × 10 23 atoms C 002 (part 1 of 1) 1 points Which of the following is NOT a correct de- scription of 16.0 grams of methane (CH 4 )? 1. the amount of methane that contains 6.022 × 10 23 C atoms 2. the amount of methane that contains two molecules of H 2 correct 3. the amount of methane that contains 4 × 6 . 022 × 10 23 H atoms 4. the amount of methane that contains 12.0 g C Explanation: MW = 16 g / mol Note that the molecular weight of methane is 16 g/mol. This was calculated by adding the mass of one carbon (12 g/mol) and 4 hydrogens (4 × 1 g/mol). This means that the 16 gram sample in the problem is equivalent to a one mole sample. Therefore it is true that the sample would have Avogadro’s number of molecules (6 . 022 × 10 23 molecules/mol). Since there are four hydrogen atoms per methane molecule, calculating the number of hydrogen atoms in one mole of methane gives ? atoms H = 1 mole CH 4 × 6 . 02 × 10 23 molec CH 4 1 mol CH 4 × 4 atoms H 1 molec CH 4 = 4 × 6 . 02 × 10 23 atoms H So this answer is also true. Now, how many grams of carbon would be in 1 mole methane? ? g C = 1 mol CH 4 × 1 mol C 1 mol CH 4

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Su, Yung – Homework 2 – Due: Sep 19 2007, midnight – Inst: FAKHREDDINE 2 × 12 g C 1 mol C = 12 g C This leaves the “contains two molecules H 2 answer as the false answer. This answer is not a correct description of 16 g methane because, while there are four hydrogen atoms, these hydrogen atoms are not bound together into diatomic hydrogen molecules. 003 (part 1 of 1) 1 points What is the mass of a single atom of the element aluminum (atomic weight 26.98)? 1.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern