General Chemistry 10th Edition

Published by Cengage Learning
ISBN 10: 1-28505-137-8
ISBN 13: 978-1-28505-137-6

Chapter 2 - Atoms, Molecules, and Ions - Questions and Problems - Page 87: 2.145

Answer

In total in 18 Ml water there are: 6 x $10^{24}$ protons 4.8x $10^{24}$ neutrons 6 x $10^{24}$ electrons

Work Step by Step

The sample contains 6.0 x $10^{23}$ molecules of water, with chemical formula $H_{2}$O. For every $H_{2}$O molecule there is 1 atom O and 2 atoms H. Therefore 6.0 x $10^{23}$ molecules of water will have 6.0 x $10^{23}$ atoms O and 2 x (6.0 x $10^{23}$) atoms H. Let us find the number of protons, neutrons, and electrons in 6.0 x $10^{23}$ atoms O. It is given that isotope oxygen-16 is present in all the molecules of water in this sample. So mass number A = 16, and we see in the periodic table of elements that Z= 8 for oxygen. So each atom oxygen has 8 protons in the nucleus, and 8 electrons in the atom. The number of neutrons would be 16 - 8 = 8 ( mass number minus atomic number, as we know that mass number is the total number of neutrons and protons in nucleus). So for 1 atom oxygen-16, there are 8 protons, 8 neutrons, and 8 electrons. For 6.0 x $10^{23}$ atoms oxygen-16 there should be: 8 x 6.0 x $10^{23}$ = 48x $10^{23}$ protons 8 x 6.0 x $10^{23}$ = 48x $10^{23}$ neutons 8 x 6.0 x $10^{23}$ = 48x $10^{23}$ electrons Let us find the number of protons, neutrons, and electrons in 2x 6.0 x $10^{23}$ atoms hydrogen-1. Number of protons for 1 atom hydrogen-1 is 1, number of neutrons for 1 atom hydrogen-1 is 0 ( 1-1=0), because mass number is 1 and atomic number is 1. number of electrons for 1 atom hydrogen-1 is 1. For 2x 6.0 x $10^{23}$ atoms hydrogen-1, there are: 1 x 2x 6.0 x $10^{23}$ = 12x $10^{23}$ protons 0 x 2x 6.0 x $10^{23}$ = 0 neutrons 1 x 2x 6.0 x $10^{23}$ = 12x $10^{23}$ electrons In total in 18 Ml water, there should be: 48x $10^{23}$ + 12x $10^{23}$ = 60 x $10^{23}$ protons 48x $10^{23}$ + 0 = 48x $10^{23}$ neutrons 48x $10^{23}$ + 12x $10^{23}$= 60 x $10^{23}$ electrons So there are: 6 x $10^{24}$ protons 4.8x $10^{24}$ neutrons 6 x $10^{24}$ electrons
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