1 / 20

Mass, density, Avogadro’s number and Moles

Mass, density, Avogadro’s number and Moles. Relative Atomic Masses. The mass of atoms in Grams is very small Ex. Oxygen = 2.67 X 10 -23 Need a better way to express these numbers Relative atomic mass Based on carbon-12 New scale needs a new Unit Atomic mass unit AMU. AMU.

nuri
Download Presentation

Mass, density, Avogadro’s number and Moles

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Mass, density, Avogadro’s number and Moles

  2. Relative Atomic Masses • The mass of atoms in Grams is very small • Ex. Oxygen = 2.67 X 10-23 • Need a better way to express these numbers • Relative atomic mass • Based on carbon-12 • New scale needs a new Unit • Atomic mass unit • AMU

  3. AMU • Carbon-12 has exactly 12 AMU’s (surprise surprise) • All other atoms are based of this assumption. • Hydrogen-1 is about 1/12 the mass carbon -12 • Therefore • = 1.007825 amu • Oxygen-16 about 12/16 of carbon-14 • therefore • =15.994915

  4. Average atomic mass • Average atomic mass • The weighted average of the atomic masses of the naturally occurring isotopes of an element. • For example • Bag full of 100 marbles • 25% have mass of 2.00 g • 75% have mass of 3.00 g • Now we add the mass times the percent of each one • (2.00x.25)+(3.00x.75)= 2.75g

  5. Lets try some! • What is the average atomic mass of copper? • Copper-63 • amu=62.929599 • abundance(%) 69.17 • Copper-65 • amu=64.927793 • abundance(%) 30.83

  6. Solved • (69.17*.62929599)+(30.83*.6492793) • 63.546 • Compare to our periodic table • Is it close • Then we are good!

  7. Another one • Oxygen-16 • AMU=15.994915 • %=99.762 • Oxygen-17 • AMU=16.999131 • %=.038 • Oxygen-18 • AMU=17.999160 • %=0.200

  8. Solved • (15.994915*.99762)+(16.999131*.0038)+(17.999160*.00200) • Three four five six don’t matter do the same thing • 15.9994 • Check the table! • Are we close

  9. The mole • MOLE • The amount of a substance that contains as many particles as the are atoms in exactly 12g of carbon -12 • This is the SI unit for the amount of a substance • Like saying a dozen.

  10. The number • Avogadro’s number • The number of particles in exactly on mole of a pure substance • 6.0221367 x 1023 • round it to 6.022 x1023 • Obtained by experiments • Best modern value

  11. The mass of a mole • Molar Mass • The mass of one mole of a pure substance • Usually written in g/mol • Equal to the atomic mass of the element on the periodic table • Ex • He=4.00g • Li=6.94g • Hg=200.59g

  12. Gram Mole conversions • We can use this information to determine molar mass and vise versa • Ex. How many grams of He are in two moles of He?

  13. Lets try some • What is the mass in grams of 2.25 mol of the element Fe? • 126 g Fe • What is the mass in grams of 0.375 mol of K? • 14.7g K

  14. Some more • What is the mass in grams of 0.0135 Na? • 0.310g Na • What is the mass in grams of 16.3 mol Ni?

  15. Density • Density • The ratio of mass to volume • Mass divided by volume

  16. Try some • What is the density of a block with a mass of 25g and a volume of 25 cm3 • What is the density of a block with a mass of 10g and a volume of 100cm3

  17. Solutions • D=25/25 • 1.0 g/cm3 • D=10/100 • 0.1 g/cm3

  18. More problems • What is the mass of a coin with a volume of 3cm3 and a density of 50g/cm3? • What is the volume of a ball with a mass of 35.8kg and a density of 10.53 g/cm3?

  19. Solutions • Solve the formula for

  20. Solution #2 • Solve the formula for

More Related