Wednesday, September 16, 2009

9-16-09: Atomic, Formula, and Molecular Weight Problem Set

Note: All atomic masses should be rounded to two decimal places before calculation, except Hydrogen (H), Helium (He), Lithium (Li), and Beryllium (Be), which should be rounded to three decimal places.

Part I. Answer the following questions. Use the periodic table to find atomic weights.

1. A silver atom weighs approximately 9 times as heavy as an atom of carbon-12. What is its atomic weight? Answer: ≈108 amu

2. Approximately how many times heavier than a carbon atom is an atom of neodymium (Nd)? Answer: 12.01 times heavier

3. Approximately how many nitrogen atoms would weigh the same as one atom of iron? Answer: ≈ 4 nitrogen atoms

4. Look at the atomic weight of chlorine in the periodic table. Suppose you are told that there are two isotopes of chlorine, namely chlorine-35 and chlorine-37. Which do you think is more abundant in nature, Cl-35 or Cl-37? Why? Answer: Cl-35, because the average atomic weight for chlorine is closer to 35 than 37.

5. There are three isotopes of hydrogen: H-1 (hydrogen), H-2 (deuterium), and H-3 (tritium). Look at the atomic weight of hydrogen on the periodic table. Which of the three isotopes do you think is most abundant in a sample of hydrogen. Answer: H-1 (Hydrogen)

Part II. Calculate the formula weight of each of the following compounds (answers in bold).

1. Na2O2 77.98

2. PCl5 208.24

3. K2SO4 174.26

4. Al(NO3)3 213.01

5. C12H22O11 342.34

6. Ca3(PO4)2 310.18

7. K2Cr2O7 294.19

8. Pb(CH3COO)4 443.376

9. Ba(CIO4)2 336.227

10. NH4HCO3 79.06

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17 comments:

  1. DuklewskiSeptember 16, 2009 at 3:24 PM

    EXTREMELY GOOD PRACTICE, TEST PREP, OR PREP FOR QUIZ!
    EXACTALY WHAT WE ARE GOING OVER
    http://gbs.glenbrook.k12.il.us/Academics/gbssci/team/chemunit30506/atomicmassisotopepractice.htm

    ReplyDelete
  2. AnonymousSeptember 16, 2009 at 3:27 PM

    This is a good site for more sample problems. It goes right along with the book, too.

    http://go.hrw.com/hrw.nd/gohrw_rls1/pKeywordResults?keyword=hc6atmx

    ReplyDelete
  3. Matt OriansSeptember 16, 2009 at 3:41 PM

    This is an extremely good website to help you out with molecular weight and many other things. great website.

    http://www.school-for-champions.com/chemistry/atomic_weight.htm

    ReplyDelete
  4. Patrick BloseSeptember 16, 2009 at 4:07 PM

    http://library.thinkquest.org/19957/chemcomp/molecularweightbody.html

    This website helps with finding molecular weight.

    ReplyDelete
  5. Peter WetzelSeptember 16, 2009 at 5:10 PM

    This Site can help find molecular weight.
    www.convertunits.com/molarmass/

    ReplyDelete
  6. Chris MathewsSeptember 16, 2009 at 5:28 PM

    remember that if you have for example (NA2OS)3 you wold multiply three by the subscript of each element. Therefore NA would be NA6 O3 and S3

    This is very important when calculating these problems

    ReplyDelete
  7. Will BrantleySeptember 16, 2009 at 5:51 PM

    Here is a molecular weight calculator so if you cant figure out a problem you can use this to find the answer:
    http://www-jmg.ch.cam.ac.uk/tools/magnus/MolWeight.html

    ReplyDelete
  8. Matt FarrellSeptember 16, 2009 at 5:53 PM

    If you are confused about how to calculate the molecular weight of a compound, this site has a video that teaches you how AND some practice problems:

    http://www.chemcollective.org/stoich/calculating_molecular_weight.php

    ReplyDelete
  9. Evan HarknettSeptember 16, 2009 at 5:56 PM

    http://dl.clackamas.edu/ch104-03/practice.htm This site has some helpful practice problems

    ReplyDelete
  10. Griff MoranSeptember 16, 2009 at 5:57 PM

    This web address has a worksheet very similar to the worksheet we had in class today. You have to find the molar mass of the compounds given.

    http://users.salineschools.com/~mccargas/Chemical%20Reactions/molar_mass1.pdf

    ReplyDelete
  11. joe "kitty" krebsSeptember 16, 2009 at 6:04 PM

    http://www.chem1.com/acad/webtext/intro/MOL.html

    helps with moles and avogadro's number

    ReplyDelete
  12. matt johnsonSeptember 16, 2009 at 6:28 PM

    Always remember that even when their are () you need to add it isn't like algebra 2 guys

    ReplyDelete
  13. Alex BlandSeptember 16, 2009 at 6:38 PM

    Worksheet for calculating molar mass of chemicals.
    http://www.mtnhomesd.org/Classrooms/Brantley/chemistry%20stuff/chemistry%20worksheets/chemistry%20ch.3/molar_mass_worksheet.htm

    ReplyDelete
  14. Andrew ParmenterSeptember 16, 2009 at 7:43 PM

    This website helps and provides tips for calculating atomic weight.

    http://chemistry.about.com/od/chemistryquickreview/a/atomicweight.htm

    ReplyDelete
  15. Donnie SheaSeptember 16, 2009 at 7:46 PM

    Good practice problems for mole-gram conversion problems:
    1)Determine the number of moles of CO2 in 454 grams. Solution and answer at: http://chemistry.about.com/od/workedchemistryproblems/a/molegramconvert.htm

    2)Determine the mass in grams of 3.60 mol of H2SO4. Solution and answer at:
    http://chemistry.about.com/od/workedchemistryproblems/a/molegramconvert_2.htm

    ReplyDelete
  16. Taylor AdkinsSeptember 16, 2009 at 7:47 PM

    Don't forget to have grams/mole after the answers in part 2

    ReplyDelete
  17. Kyle McCafferySeptember 16, 2009 at 8:13 PM

    http://environmentalchemistry.com/yogi/reference/molar.html

    This website takes calculating the mass of a compound step by step.

    ReplyDelete

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