# Cl-35 has an atomic weight of #"34.9689# and Cl-37 has an atomic weight of #"36.9695#. What is the percent abundance of Cl-35?

##### 1 Answer

The percent abundance of Cl-35 = 76.0%.

#### Explanation:

The percent abundance of chlorine-35 and chlorine-37 must equal 100, or, in decimal form 1.

**Given/Known:**

atomic weight of Cl-35

atomic weight of Cl-37

atomic weight of chlorine

**Unknown:**

**SOLUTION:**

**1. Set up the equation as follows:**

**2. Carry out multiplication.**

**3. Combine the x values.**

**4. Subtract 36.9695 from both sides.**

(rounded to two decimal places due to significant figure rounding rules for addition and subtraction)

**5. Divide both sides by -2.0006 to calculate abundance.**

(rounded to three significant figures due to rounding rules for multiplication and division)

(In this case 1 is an exact number, which has an infinite number of significant figures, so significant figures are dependent upon

**6. Multiply abundance times #100%# to get percent abundance.**