Question

Molar Mass (g/mol)

N	14.007
H	1.0080

A pure sample of a compound that contains phosphorus and oxygen weighs 1.164 g. If the sample is found to contain 0.508 g of phosphorus , what is the empirical formula of the compound?

Molar Mass (g/mol)

P	30.974
O	15.999

A pure sample of a compound that contains nitrogen and hydrogen weighs 1.555 g. If the sample is found to contain 1.359 g of nitrogen, what is the empirical formula of the compound?

Answer 1

1)

we have mass of each elements as:

P: 0.508 g

O: 1.164 - 0.508 = 0.656 g

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

P: 0.508/30.97 = 0.0164

O: 0.656/16.0 = 0.041

Divide by smallest:

P: 0.0164/0.0164 = 1

O: 0.041/0.0164 = 2.5

Multiply by 2 to get simplest whole number ratio:

P : 1*2 = 2

O : 2.5*2 = 5

So empirical formula is:P2O5

2)

we have mass of each elements as:

N: 1.359 g

H: 1.555 - 1.359 = 0.196 g

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

N: 1.359/14.01 = 0.097

H: 0.196/1.008 = 0.1944

Divide by smallest to get simplest whole number ratio:

N: 0.097/0.097 = 1

H: 0.1944/0.097 = 2

So empirical formula is:NH₂