Question

atomic mass
elements come in a variety of isotopes, meaning they are made up of atoms with the same atomic number but different atomic masses. these atoms differ in the number of neutrons.
the average atomic mass is the weighted average of all the isotopes of an element.
example: a sample of calcium is 75% ¹³³ca, 20% ¹³²ca and 5% ¹³⁴ca. what is its average atomic mass?
answer:.75 x 133 = 99.75
.20 x 132 = 26.4
.05 x 134 = 6.7
total = 132.85 amu = average atomic mass
determine the average atomic mass of the following mixtures of isotopes.

1. 80% ¹²⁷i, 17% ¹²⁴i, 3% ¹²⁸i
2. 50% ¹⁹⁷au, 50% ¹⁹⁸au
3. 15% ⁵⁴fe, 85% ⁵⁶fe
4. 99% ¹h, 0.8% ²h, 0.2% ³h
5. 95% ¹⁴n, 3% ¹⁵n, 2% ¹⁴n
6. 98% ¹²c, 2% ¹⁴c

Explanation:

Step1: Calculate for 1st mixture

$0.80\times127 + 0.17\times124+0.03\times126$
$=101.6+21.08 + 3.78$
$=126.46$

Step2: Calculate for 2nd mixture

$0.50\times197+0.50\times198$
$=98.5 + 99$
$=197.5$

Step3: Calculate for 3rd mixture

$0.15\times54+0.85\times56$
$=8.1+47.6$
$=55.7$

Step4: Calculate for 4th mixture

$0.99\times1+0.008\times2+0.002\times3$
$=0.99 + 0.016+0.006$
$=1.012$

Step5: Calculate for 5th mixture

$0.95\times14+0.03\times15+0.02\times14$
$=13.3+0.45 + 0.28$
$=14.03$

Step6: Calculate for 6th mixture

$0.98\times12+0.02\times14$
$=11.76+0.28$
$=12.04$

Answer:

1. $126.46$
2. $197.5$
3. $55.7$
4. $1.012$
5. $14.03$
6. $12.04$