Question

Cholrine has an average atomic mass of 35.45 amu. The two naturally occurring isotopes of chlorine are chlorine-35 and chlorine-37. do most chlorine atoms contain 18 neutrons or 20 neutrons? why?

Answer 1

let the moles of chlorine-35 is n1 and chlorine-37 is n2

now we will use the formula of average atomic mass

$M = \frac{n_1M_1 + n_2M_2}{n_1 + n_2}$

here let say

$\frac{n_1}{n_2} = x$

$35.45 = \frac{x(35) + 37}{x + 1}$

$35.45 x + 35.45 = 35x + 37$

$35.45 x - 35 x = 37 - 35.45$

$0.45 x = 1.55$

$x = 3.44$

so here since ratio of moles of chlorine 35 and chlorine 37 is more than 1 so chlorine 35 is more in the proportion in this mixture so there is most chlorine atom consist of 18 neutrons

Answer 2

Answer:

chlorine-35

Explanation:

We are given that Chlorine has an average atomic mass=35.45 amu

The two naturally occurring isotopes of chlorine are chlorine -35 and chlorine -37.

We have to find which isotope  most contain 18 neutrons or 20 neutrons and why.

Let

$\frac{x}{y}=a$

Where x= Part of chlorine-35

y=Part of chlorine-37

Then, x=a and y=1

Average atomic mass=$\frac{m_1x_1+m_2x_2}{x-1+x_2}$

Using this formula

$35.45=\frac{35a+37}{a+1}$

$35.45a+35.45=35a+37$

$35.45a-35 a=37-35.45=1.55$

$0.45 a=1.55$

$a=\frac{1.55}{0.45}=3.44$

The ratio of two isotopes is 3.44 which is greater than 1.

Therefore,chlorine-35 is greater than chlorine-37 in a mixture of two isotopes.

We know that atomic number of chlorine-35 is 17.

Neutron number=35-17=18

Hence, the chlorine-35 is most which contain 18 neutrons.