Average Atomic Mass Worksheet 2Name: ______
AP Chemistry
Show your work for each of the following problems.
Calculation of average atomic mass is not a straight average but a weighted averagebased upon the percent isotopic ratio of the element. The following general formula can be used in all cases.
What is the average atomic mass of the following isotopic mixtures? Show your work!!
1) 22.00% of 159.3 amu; 78.00% of161.2 amu.
2) 42.10 amu - 93.50%; 48.30 amu - 6.200%; 50.40 amu - 0.3000%
3)75.0 % 133Cs with a mass of 132.97 amu, 20.0 % 132Cs with a mass of 131.98 amu, and 5.00 % 134Cs with a mass of 133.982 amu
4)80.00 % 127I with a mass of 126.963 amu, 17.00 % 126I with a mass of 125.984 amu, 3.00 % 128I with a mass of 127.992 amu
5)50.00 % 197Au with a mass of 196.798 amu, 50.00 % 198Au with a mass of 197.882 amu
6) 15.35 % 55Fe with a mass of 54.997 amu, 84.65 % 56Fe with a mass of 55.989 amu
7) 99.00 % 1H with a mass of 1.0003 amu, 0.8000 % 2H with a mass of 2.0074 amu, 0.2000 % 3H with a mass of 3.0121 amu
8)Find the average atomic mass for Li if 7.50% of Li atoms are 6Li with amass of 6.0151223 amu and 92.5% are 7Li with a mass of 7.0160041 amu.
9)Find the average atomic mass for B if 19.9% of B atoms are 10B with a massof 10.0129371 amu and 80.1% are 11B with a mass of 11.0093055 amu.
10)Find the average atomic mass for Cl if 75.78% of Cl atoms are 35Cl with amass of 34.96885271 amu and 24.22% are 37Cl with a mass of36.96590260 amu.
11 Find the average atomic mass for Mg if 78.99% of Mg atoms are 24Mgwith a mass of 23.9850419 amu, 10.00% are 25Mg with a mass of24.9858370 amu, and 11.01% are 26Mg with a mass of 25.9825930 amu.
12) There are 2 isotopes of copper that occur naturally; 63Cu and 65Cu. The63Cu atoms which occur 77.93 % of the time have a mass of 62.929601 amu and the 63Cu atoms have a massof 64.927794 amu.
13) There are 2 isotopes of gallium that occur naturally; 69Ga and 71Ga. The69Ga atoms which occur 19.32% of the time have a mass of 68.925581 amu and the 71Ga atoms have amass of 70.924707 amu.
14) Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of85Rb which has an atomic mass of 84.974 amu is 72.2% and the abundance of 87Rb which has an atomic mass of 86.973 amu is 27.8%, what is the averageatomic mass of rubidium?
15) Uranium has three common isotopes. If the abundance of 234U which has an atomic mass of 233.878 amu is 0.01%,the abundance of 235Uwhich has an atomic mass of 234.892 amu is 0.71%, and the abundance of 238Uwhich has an atomic mass of 237.911 amu is 99.28%,what is the average atomic mass of uranium?
16) Titanium has five common isotopes: 46Ti (8.00%, 45.983 amu), 47Ti (7.80%, 46.988 amu), 48Ti (73.4%, 47.910 amu),49Ti (5.50%, 48.923 amu), 50Ti (5.30%, 49.942 amu). What is the average atomic mass of titanium?
17) What is the average atomic mass of silver if 51.84% of silver atoms have a mass of 106.905amu and 48.16% of them have a mass of 108.905 amu?
18) Find the average atomic mass of krypton using the data below:
Isotope Mass (AMU) / Percentage Abundance (%)77.920 / 0.350
79.916 / 2.27
81.913 / 11.56
82.914 / 11.55
83.912 / 56.90
85.911 / 17.37
19) Calculate the average atomic mass of chromium, given the following percent abundances andisotopic masses.
Isotope Mass (AMU) / Percentage Abundance (%)49.946 / 4.345%
51.941 / 83.789%
52.941 / 9.501%
53.939 / 2.365%
20) Calculate the average atomic mass of indium if 4.3% of its atoms are indium-113 with an atomic mass of 112.941 amu and 95.7% of its atoms are indium-115 with an atomic mass of 114.943 amu.
21) Explain why atoms have different isotopes. In other words, how is it thathelium can exist in three different forms?