Question

calculating average atomic mass - round average atomic mass to 3 decimal places

1. nitrogen

isotope	mass number	percent abundance
$^{15}_{7}n$	15	0.37%

average atomic mass =

1. argon

isotope	mass number	percent abundance
$^{38}_{18}ar$	38	0.06%
$^{40}_{18}ar$	40	99.60%

average atomic mass =

on this problem, you will need to calculate the average atomic mass and fill in the blanks in the chart.

1. tin

isotope	mass number	percent abundance
	115	23.60%
	118	22.60%
	120

average atomic mass =

1. krypton

isotope	mass number	percent abundance
	86

average atomic mass =

Explanation:

Step1: Recall average atomic mass formula

The formula for average atomic mass is $\sum_{i}(m_i\times p_i)$, where $m_i$ is the mass - number of the isotope and $p_i$ is the percent abundance (expressed as a decimal) of the isotope.

Step2: Calculate average atomic mass of nitrogen

For nitrogen:
$m_1 = 14$, $p_1=0.9963$; $m_2 = 15$, $p_2 = 0.0037$
Average atomic mass $=14\times0.9963 + 15\times0.0037=14\times0.9963+15\times0.0037=13.9482 + 0.0555=14.004$

Step3: Calculate average atomic mass of argon

For argon:
$m_1 = 36$, $p_1 = 0.0034$; $m_2 = 38$, $p_2=0.0006$; $m_3 = 40$, $p_3 = 0.9960$
Average atomic mass $=36\times0.0034+38\times0.0006 + 40\times0.9960=0.1224+0.0228 + 39.84=39.985$

Step4: Calculate average atomic mass of tin (incomplete data, assume remaining abundances sum to $100-(1.50 + 23.60+22.60)=52.30\%$ and mass - number of the remaining isotope is 119 for simplicity)

$m_1 = 114$, $p_1 = 0.0150$; $m_2 = 115$, $p_2 = 0.2360$; $m_3 = 118$, $p_3 = 0.2260$; $m_4 = 119$, $p_4 = 0.5230$
Average atomic mass $=114\times0.0150+115\times0.2360+118\times0.2260+119\times0.5230$
$=1.71+27.14+26.668+62.237=117.755$

Step5: Calculate average atomic mass of krypton (incomplete data, assume remaining abundance is $100 - 50.69=49.31\%$ and mass - number of the remaining isotope is 84 for simplicity)

$m_1 = 82$, $p_1 = 0.5069$; $m_2 = 84$, $p_2 = 0.4931$
Average atomic mass $=82\times0.5069+84\times0.4931=41.5658+41.4204=82.986$

Answer:

1. $14.004$
2. $39.985$
3. $117.755$
4. $82.986$