### Bonus Empirical Formula Problem Answers 1 & 2

**Problem #1:** Calculate the molar mass of a metal that forms an oxide having the empirical formula M_{2}O_{3} and contains 68.04% of the metal by mass. Identify the metal.

**Solution**

(1) 68.04% of the compound is the metal, therefore 31.96% is oxygen.

(2) The three oxygens weigh 48.0 and this represents 31.96% of the total weight.

(3) 31.96% is to 48.0 as 100% is to x

x = 150.2

(4) Subtract 48 from 150.2 to get 102.2, which is the weight contribution of M_{2}.

(5) Dividing by two gets 51.1. The nearest atomic weight on the periodic table is 50.9, that of vanadium.

**Problem #2:** Hemoglobin is the oxygen carrying compound found in human blood. It is found to contain 0.3335% iron by mass. It is already known that one molecule of hemoglobin contains four atoms of iron. What is the molecular mass of hemoglobin?

**Solution**

(1) One iron weighs 55.845; four of them weigh 223.38

(2) This value (223.38) represents 0.3335% of the total mass of hemoglobin.

(3) 223.38 is to 0.3335% as x is to 100%

(4) x = 66,980 g/mol

Comment: in biochemistry, molecular weights into the tens of thousands are very common. Also, the unit "daltons," as a symbol for g/mol, is often used in biochemistry, as in 66,980 daltons.