Time remaining:
What are the natural abundances of the other two isotopes? 25Mg and 26Mg. In %.

Chemistry
Tutor: None Selected Time limit: 1 Day

There are 3 stable isotopes of magnesium. Their masses are 23.9850, 24.9858 and 25.9826 amu. If the average atomic mass of magnesium is 24.3050 amu and the natural abundance of the lightest isotope is 78.99%.

Oct 5th, 2014

Given Magnesium 24 is in abundance of 78.99 %.

Therefore amount remaining = 100-78.99%=21.01%

Now this 21% is equal to (Magnesium 25 + Magnesium 26)

take Mg-25 = X

and Mg-26=21.01 - X

Given average atomic mass of magnesium = 24.3050 amu

24.3050 = (0.7899) x (23.9850) + (X) x ( 24.9858) + (0.2101-x) x 25.9826

24.3050 = 18.9457 + 24.9858 X + [ ( 25.9826 x 0.2101) - (25.9826 x X)]

24.3050 = 18.9457 + 24.9858X + 5.4589 - 25.9826 X

24.3050=18.9457 +5.4589 +24.9858X-25.9826X

24.3050 = 24.4046-0.9968X

24.3050-24.4046 = -0.09968X

-0.0996=-0.09968X

X=-0.0996/-0.08868=0.09991


therefore Mg-25= X = 0.09991 Multiply by 100 = 9.991%

 and Mg-26 =21.01-X=21.01-9.991 = 11.019%



Oct 5th, 2014

Are you studying on the go? Check out our FREE app and post questions on the fly!
Download on the
App Store
...
Oct 5th, 2014
...
Oct 5th, 2014
Dec 6th, 2016
check_circle
Mark as Final Answer
check_circle
Unmark as Final Answer
check_circle
Final Answer

Secure Information

Content will be erased after question is completed.

check_circle
Final Answer