(4) What is the empirical formula of the compound?
The empirical formula identifies the relative amounts of the elements. The previous problem shows that there is three times as much hydrogen as phosphorous and four times as much oxygen as phosphorous. Assigning phosphorous a base coefficient of one, the empirical formula must be
(5) What is the molecular formula of the compound?
Not enough information is given in the problem to determine the molecular formula. The actual compound could be and still obey the restrictions given in the problem. If the molecular mass of the compound were given, the molecular mass of the compound derived in question 3 could be compared to the given molecular mass to determine the molecular formula. (The comparison would yield a whole number identifying by what factor the subscripts of the empirical formula must be multiplied to obtain the molecular formula.) Additionally, if the sample were identified as a sample of phosphoric acid, the empirical formula could be identified as the molecular formula because is the molecular formula for phosphoric acid. However, without one of these identifying pieces of information, the molecular formula cannot be determined.
