Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chemistry Lab Atomic Structure Name __________________________6/06 Date ___________ Period ______ ISOTOPES AND AVERAGE ATOMIC MASS INTRODUCTION The atomic mass of an element is the sum of all the masses of the sub-atomic particles which comprise the atom. The mass in grams of these particles (protons, neutrons, electrons, et al) are exceptionally small. The mass of the proton is 1.67 X 10-23 grams. The neutron is slightly larger and the electron is much smaller. For any given atom, the number of protons and electrons can not vary. However, the number of neutrons may vary from atom to atom of the same element. This causes the mass of atoms of the same element to vary. Atoms of the same element with different atomic masses are called ISOTOPES. To obtain the best value of the mass of an element, we would need to consider the various masses of the atoms of that element and the percentage of all atoms of that element with those masses. We would need to find the "weighted" average of the masses. Consider the diagram below: 14 12 12 14 12 12 12 12 12 12 12 12 14 12 The average mass be for the sample of atoms below is not thirteen due to many more atoms which weigh twelve: In this lab you will determine the "atomic mass" of the hypothetical element Beanium (Bn). PROCEDURE 1. Obtain a sample of Beanium atoms. 2. Determine the total number of atoms in your sample. 3. Count the number of atoms of each isotope. 4. Calculate the percent abundance of each isotope by dividing the number of atoms of each isotope by the total number of atoms. 5. Calculate the mass of each isotope by massing 10 atoms on the electronic balance and dividing by 10 (you are therefore determining the mass of ONE typical atom of the isotope.) 6. Calculate the average atomic mass of Beanium (Bn) by multiplying the percent abundance of each isotope times that isotope’s atomic mass for each isotope and adding all of the products. DATA 1. Total number of "atoms" 2. Number of isotope 1 “atoms” Number of isotope 2 “atoms” Number of isotope 3 “atoms” 3. Mass one (1) atom of isotope 1 Mass of one (1) atom of isotope 2 Mass of one (1) atom of isotope 3 4. Mass of all Beanium atoms (actual) CALCULATIONS: Show all work!!! (Since all numbers are “exact values” calc. All % to +/- .1%) 1. % isotope 1 % isotope 2 % isotope 3 2. Average atomic mass of Beanium = (% isotope 1) (mass isotope 1) + (% isotope 2) (mass isotope 2) + (% isotope 3) (mass isotope 3) 3. Actual average mass (mass of all Beanium atoms on electronic balance 4. % error = average atomic mass – actual mass x 100% average atomic mass QUESTIONS: 1. What is an isotope? 2. Are C-14 and N-14 isotopes? Explain your reasoning. 3. How do the different beans represent isotopes? 4. In a given sample element X-25 is found in 65.0% abundance, element X-27 in 25.0% abundance and element X-29 in 10% abundance. Is the weighted average mass closest to X-25, X-27 or X-29. Justify your answer. 5. Calculate the average atomic mass of the substances below: % Abundance symbol Mass (amu) 75.53 Cl-35 34.969 24.47 Cl-37 36.966