January 25th - Mass to Moles to Moles to Mass

Today, we were able to learn how to go from one mass to another mass. We've already learned all the tools we need to do this, and all we need is this chart:

To correctly move from Mass A to Mass B, we must first go to moles of both substances. To refresh, here is a detailed step-by-step procedure for these type of questions.

1)    Write a balanced chemical formula.

2)    Find the mass of your first substance, and using molar mass, convert it to moles.

3)    Using mole to mole conversions, change mole A to mole B (using coefficients of the balanced equation). Remember, always put what you need over what you have.

4)    Finally, move from moles B to mass B by simply using the molar mass of the new substance.

If you're really good, numbers two through four can be accomplished in a single dimensional analysis equation.

Let’s try an example.

Ex.)  Limestone (calcium carbonate) is heated to produce calcium oxide and carbon dioxide. How much limestone is needed to produce 10kg of calcium oxide?

CaCO₃ à CaO + CO₂

10 000g CaO (1 mol CaO/56.1g CaO) (1 mol CaCO₃ / 1 mol CaO) ( 100g CaCO₃ / 1 mol CaO)
= 1.78 x 10⁴ g or 17.8kg.

That is all you have to do! All it takes is one additional conversion from our previous equations. And since we have all the tools needed, it should be a snap!

For additional practice, the following video is provided:

Posted by Andrew.