Question

Phosphoric acid, which is a component of many soft drinks, has a molar mass of 98.00 grams per mole. A sample of phosphoric acid contains 3.1 percent hydrogen, 31.6 percent phosphorus, and 65.3 percent oxygen by mass. What is the molecular formula of phosphoric acid

Answer 1

Answer:

$H_{3} PO_{4}$

Explanation:

We start this question by assuming we have 100 g of phosphoric acid. Based on the percentages, this means 3.1 g of it is hydrogen, 31.6 g of it is phosphorus and 65.3 of it is oxygen. Now we can calculate the empirical formula

H : 3.1/1.008 = 3.075 ≈ 3

P : 31.6/30.97 = 1.020 ≈ 1

O : 65.3/15.99 = 4.08 ≈ 4

This would mean that its formula is H3PO4 which has a relative molecular mass of 3 (1.008) + 1(30.97) + 4(15.99) =  97.954. Since the empirical molecular mass is equal to the molar mass of this substance in grams, then we have found the molecular mass