Question

the mass spectrum of a sample of a pure element is shown above. calculate the average atomic mass of the element. what is the identity of the element?

Explanation:

Step1: Identify isotopic masses and abundances

Let the isotopes have masses $m_1 = 39$, $m_2=40$, $m_3 = 41$ and abundances $a_1=93.26\%=0.9326$, $a_2 = 0.01\%=0.0001$, $a_3=6.73\% = 0.0673$.

Step2: Use average - atomic - mass formula

The formula for average atomic mass $A=\sum_{i}m_ia_i$. So $A=(39\times0.9326)+(40\times0.0001)+(41\times0.0673)$.

Step3: Calculate the result

$A = 39\times0.9326+40\times0.0001 + 41\times0.0673=38.9644+0.004+2.7593=39.0277\approx39.03$.

Answer:

The average atomic mass is approximately 39.03. To identify the element, we look up this value on the periodic - table. The element with an average atomic mass close to 39.03 is potassium (K).