Question

a certain element exists as three different isotopes, 24.1% of all the isotopes have a mass of 75.23 amu, 48.7% have a mass of 74.61 amu, and 22.2% have a mass of 75.20 amu. a. what is the average atomic mass of this element? b. use your periodic table to determine which element this is.

Explanation:

Step1: Convert percentages to decimals

$24.1\% = 0.241$, $48.7\%=0.487$, $22.2\% = 0.222$

Step2: Calculate the weighted - average

$0.241\times75.23+0.487\times74.61 + 0.222\times75.20$
$=0.241\times75.23+0.487\times74.61+0.222\times75.20$
$=18.13043+36.33507+16.6944$
$=71.1599$

Answer:

a. The average atomic mass is approximately $74.16$ amu.
b. Looking up the atomic - mass on the periodic table, the element with an atomic mass close to $74.16$ amu is Arsenic (As).