te Undergr D The Purdue rs n Chapter 3-Atems, the Building Bleche of Clenents Ch

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te Undergr D The Purdue rs n Chapter 3-Atems, the Building Bleche of Clenents Chapter 3 Review Questions Amanda Brock Feb 21, 2018 11:5944 PM Return to Site (14 of 25) Calculate the isotope mass of Ga71 f the atomic mass of goalium is 69.7 g/mol and one of its two isotopes has the following relative mass and percent Ga69 689256 gmol 60.11% 72.3 69.2 70.9 703 Skip Qvestien Note: Clicking any button other than the Save Answer button will NOT save ary changes to your answers 7 For questions or concems rearding this onllne Having trobles viewing something on the M,"20 is a trodemark of Great Riv publication, please contaer eb the comect MacBook Air 0 5 6 7 8

Explanation / Answer

Ans. #14. Given,       content of 69Ga = 60.11 %

So, content of 71Ga = 100.000 % - % 69Ga = 100.000 % - 60.11% = 39.89 %

Let the atomic mass of 71Ga isotope = Y

Now,

Average atomic mass = (% 69Ga x its atomic mass) + (% 71Ga x its atomic mass)

Or, 69.7 g mol-1 = (60.11 % x 68.9256 g mol-1) + (39.89 % x Y)

Or, 69.7 g mol-1 = 41.43117816 g mol-1 + 0.3989 Y                               ; [ Y % = Y/ 100]

Or, 0.3989 Y = 69.7 g mol-1 - 41.43117816 g mol-1 = 28.26882184 g mol-1

Or, Y = 28.26882184 g mol-1 / 0.3989 = 70.869 g mol-1

Therefore, atomic mass (isotope mass) of 71Ga = 70.869 g mol-1 = 70.9 g/ mol

# Therefore, correct option is- C. 70.9

#15. Moles of selenium = Mass / Molar mass

                                    = 43.8 g/ (78.96 g/ mol)

                                    = 0.5547 mol

# Number of Se-atoms = Number of moles x Avogadro number

                                    = 0.5547 mol x (6.022 x 1023 atoms/ mol)

                                    = 3.34 x 1023 atoms

So, correct option is- D. 3.34 x 1023

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