Question

Cacodyl, a compound used in the manufacture of herbicide, has a molar mass of 209.96 g/ mol. Its mass composition is 22.88% C, 5.76% H, and 71.36% As. Show all work.

a) What is the empirical formula of cacodyl?

b) What is the molecular formula of cacodyl?

Answer 1

a)

we have mass of each elements as:

C: 22.88 g

H: 5.76 g

As: 71.36 g

Divide by molar mass to get number of moles of each:

C: 22.88/12.01 = 1.9051

H: 5.76/1.008 = 5.7143

As: 71.36/74.92 = 0.9525

Divide by smallest to get simplest whole number ratio:

C: 1.9051/0.9525 = 2

H: 5.7143/0.9525 = 6

As: 0.9525/0.9525 = 1

  

So empirical formula is:C₂H₆As

b)

Molar mass of C2H6As = 2*MM(C) + 6*MM(H) + 1*MM(As)

= 2*12.01 + 6*1.008 + 1*74.92

= 104.988 g/mol

Now we have:

Molar mass = 209.96 g/mol

Empirical formula mass = 104.988 g/mol

Multiplying factor = molar mass / empirical formula mass

= 209.96/104.988

= 2

So molecular formula is:C₄H₁₂As₂