Chapter 42, Problem 019 Your answer is partially correct. A periodic table might

Question

Chapter 42, Problem 019 Your answer is partially correct. A periodic table might list the average atomic mass of magnesium as being 24.312 u. That average value is the result of weighting the atomic masses of the magnesium isotopes according to their natural abundances on Earth.The three isotopes and their masses are 24Mg (23.98504 u), 25Mg (24.98584 u), and 26Mg (25.98259 u). The natural abundance of 24Mg is 78.99 % by mass (that is, 78.99 % of the m ass of a naturally occurring sample of magnesium is due to the presence of 24Mg).What is the abundance of (a)25Mg and (b)26Mg? (a) NumberT11.707 percent (b) Number TT9.303

Explanation / Answer

Abundance of 25 and 26 will be 21.01 %, hence we will have to devide this to get their respective proportion.

Let their combined mass be M

78.99 * 23.98504 + 21.01* M = 100 * 24.312

M = 25.541 u

let the share of 25 be x

x *24.98584 + (21.01 -x) 25.98259 = 21.01* 25.541

x = 9.303 is the percentage of 25 and 11.707 is the percentage of 26.

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