Density and Moles

As mentioned in an earlier post and hopefully common knowledge by this point, density is a measure of mass per volume. It is best defined by this formula:

As density is a quantitive measure of both mass or volume, the units used are g/L or g/mL. 

In molar conversions, density becomes an extension of mass that is solved either dividing or multiplying by it. Several examples are below. 

Example One: 

Water has a density of 1.0 g/mL. Determine the mass of 11.5 mL of water. 

        11.5 mL x (1g/1mL) = 11.5 grams  

How many moles are in 11.5 mL of water? 

        11.5g x (1 mol/18 g) = 0.639 mole  

Example Two:

If a gold ring has a volume of 7.50 mL and contains 0.736 mol of Gold determine the density of gold. 

        0.736 mol x (197.0 g/1 mol) = 145 g 

      

        D = (145 g/7.50 mL) 

            = 19 g/mL  

-Simon Sierra