The table below shows data for two isotopes of chlorine ([tex]$Cl$[/tex]). The data in the "\% Abundance" column represents the likelihood that any given atom of chlorine is a particular isotope.

\begin{tabular}{|c|c|c|}
\hline
Isotope & Mass (amu) & \% Abundance \\
\hline
[tex]${ }^{35}Cl$[/tex] & 34.97 & 75.78 \\
\hline
[tex]${ }^{37}Cl$[/tex] & 36.97 & 24.22 \\
\hline
\end{tabular}

What is the weighted average mass of chlorine?

A. 26.50
B. 34.97
C. 35.45
D. 35.97



Answer :

To find the weighted average mass of chlorine based on the given isotopes and their abundances, follow these steps:

1. Identify the masses and abundances:
- Isotope [tex]\({}^{35}Cl\)[/tex] has a mass of 34.97 amu and an abundance of 75.78%.
- Isotope [tex]\({}^{37}Cl\)[/tex] has a mass of 36.97 amu and an abundance of 24.22%.

2. Convert the percentages to decimals:
- For [tex]\({}^{35}Cl\)[/tex]: 75.78% becomes 0.7578
- For [tex]\({}^{37}Cl\)[/tex]: 24.22% becomes 0.2422

3. Calculate the contribution of each isotope to the weighted average mass:
- Contribution of [tex]\({}^{35}Cl\)[/tex]: [tex]\( 34.97 \times 0.7578 \)[/tex]
- Contribution of [tex]\({}^{37}Cl\)[/tex]: [tex]\( 36.97 \times 0.2422 \)[/tex]

4. Sum these contributions to get the weighted average mass:
[tex]\[ (34.97 \times 0.7578) + (36.97 \times 0.2422) \][/tex]

5. Perform the calculations:
- [tex]\( 34.97 \times 0.7578 = 26.502866 \)[/tex]
- [tex]\( 36.97 \times 0.2422 = 8.951534 \)[/tex]

6. Add these values together:
[tex]\[ 26.502866 + 8.951534 = 35.4544 \][/tex]

Therefore, the weighted average mass of chlorine is [tex]\( 35.4544 \, \text{amu} \)[/tex].

The correct answer is:
C. 35.45