A compound contains 26.7% phosphorus, 12.1% nitrogen, and 61.2% chlorine. It’s molar mass is 695 g/mol. Find the molecular formula of the compound.

Question

Please help asap. I already cried over this twice and I just don't understand. Thank you in advance.

Answer 1

Hi Alli,

The first step is to find out how many grams of each element are in one mole of the compound. We can do this because we've been given the molar mass of the compound, as well as the percent mass of each element.

695g * 26.7% = 186g of Phosphorous/mol of compound.

695g * 12.1% = 84g of Nitrogen/mol of compound.

695g * 61.2% = 425g of Chlorine/mol of Compound.

Now that we know how many grams of each element are present per mole of compound, we can use the molar masses of each element to find out how many moles of each element are present per mole of the compound.

186g P * (1mole P/30.1g) = Approximately 6 moles of Phosphorous.

84g N * (1mole N/14g) = Approximately 6 moles of Nitrogen.

425g Cl * (1mole/35g) = Approximately 12 moles of Chlorine.

Therefore, the chemical formula for this compound would be N₆Cl₁₂P₆. We can double check by making sure that a compound with this formula has the same molar mass as the one you were given in the problem.

(6*14) + (35.45*12) + (31*6) = 695.4 grams!

Hope this helped.