R02-A - CHEM 111 Recitation Week #3 February 5th & 7th,...

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CHEM 111 Recitation Week #3 Name: ANSWER KEY February 5 th & 7 th , 2008 (10 points) Section: Some possibly useful information average atomic mass = Σ [(isotope mass) x (fractional isotope abundance)] E = h ν νλ = c E n = –2.18 x 10 -18 J Z 2 n 2 " # $ % & h = 6.626 x 10 –34 J-s c = 3.00 x 10 8 m/s 1. Complete the table assuming all of the atoms are electrically neutral. Atom # Protons # Neutrons Chemical Symbol # Electrons manganese 25 30 55 Mn 25 bismuth 83 126 209 Bi 83 xenon 54 75 129 Xe 54 cesium 55 78 133 Cs 55 helium 2 1 3 He 2 For the following calculations, show all of your work, and report your answers with the correct number of significant figures and units. 2. Given the information below, calculate the average atomic mass of magnesium (Mg). 24 Mg: mass = 23.985 amu; percent abundance = 78.99% 25 Mg: mass = 24.986 amu; percent abundance = 10.00% 26 Mg: mass = 25.983 amu; percent abundance = 11.01% (1 point) 4 sig figs needed, specifically 2 are needed after the decimal (23.985 " 0.7890) + (24.986 " .1000) + (25.983 " .1101) = 24.31 amu 3. Copper has two naturally occurring isotopes, 63 Cu (mass = 62.9296 amu) and 65 Cu (mass = 64.9278 amu). Calculate the % abundances of the two isotopes of Cu.
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This homework help was uploaded on 04/20/2008 for the course CHEM 111 taught by Professor Grzegorz during the Spring '08 term at Colorado State.

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R02-A - CHEM 111 Recitation Week #3 February 5th & 7th,...

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