Question

Determine the molecular and empirical formula of a compound that contains 26.7% P, 12.1% N, and the remainder is Cl. One molecule has a mass of 9.63x10^-22 g.

Answer 1

1)

we have mass of each elements as:

P: 26.7 g

N: 12.1 g

Cl: 61.2 g

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

P: 26.7/30.97 = 0.862125

N: 12.1/14.01 = 0.863669

Cl: 61.2/35.45 = 1.726375

Divide by smallest to get simplest whole number ratio:

P: 0.862125/0.862125 = 1

N: 0.863669/0.862125 = 1

Cl: 1.726375/0.862125 = 2

  

So empirical formula is:

PNCl2

2)

molar mass = mass of 1 mol

= mass of one molecule * 6.022*10^23

= 9.63*10^-22 * 6.022*10^23

= 579.9 g/mol

Molar mass of PNCl2,

MM = 1*MM(P) + 1*MM(N) + 2*MM(Cl)

= 1*30.97 + 1*14.01 + 2*35.45

= 115.88 g/mol

Now we have:

Molar mass = 579.9 g/mol

Empirical formula mass = 115.88 g/mol

Multiplying factor = molar mass / empirical formula mass

= 579.9/115.88

= 5

Hence the molecular formula is : P5N5Cl10