Question

Chlorine is made up of 75.78% 35Cl and 24.22% 37Cl.

Answer 1

If 35Cl = 34.969 amu and 37Cl = 36.966 amu

Average atomic mass of the sample of chlorine..;

; [34.969(75.78) + 36.966(24.22)] ÷ 100....,where 100 is the total percentage.

; 3545.267 ÷ 100

; Hence the average atomic mass....,

35.453 amu

Answer 2

Answer: The average atomic mass of chlorine is 35.453 amu.  

Explanation:

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.  

Formula used to calculate average atomic mass follows:

$\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i$   .....(1)

• For $_{17}^{35}\textrm{Cl}$ isotope:

Mass of $_{17}^{35}\textrm{Cl}$ isotope = 34.969 amu

Percentage abundance of $_{17}^{35}\textrm{Cl}$ isotope =  75.78 %

Fractional abundance of $_{17}^{35}\textrm{Cl}$ isotope = 0.7578

• For $_{17}^{37}\textrm{Cl}$ isotope:

Mass of $_{17}^{37}\textrm{Cl}$ isotope = 36.966 amu

Percentage abundance of $_{17}^{37}\textrm{Cl}$ isotope = 24.22 %

Fractional abundance of $_{17}^{37}\textrm{Cl}$ isotope = 0.2422

Putting values in equation 1, we get:  

$\text{Average atomic mass of Chlorine}=[(34.969\times 0.7578)+(36.966\times 0.2422)]$

$\text{Average atomic mass of chlorine}=35.453amu$

Hence, the average atomic mass of chlorine is 35.453 amu.