Mole Conversions

Let us start with a relatively simple mole conversion problem.

What is the mass (in grams) of 0.050 moles of calcium hydroxide?

Before starting, consider what tools you will need to solve this problem. I will assume all of you have some paper, pencil, a standard calculator, and a periodic table. This problem introduces some new levels of difficulty. The student must now be able to write the correct chemical formula, but understand the intricacies of calculating the molar mass from the formula. (Alternatively, imagine you had assigned this problem to work out in class. How would you respond to each of the answers given to you by the students?)

Entering Formulas

(We will work on this problem by opening up the Calculate Mode window, the use of which was introduced in working through the first problem.) First, enter "0.050 mol" using the Numeric- and Units keypad (or the computer keyboard). You can use the periodic table and Numeric keypad to write the chemical formula of calcium hydroxide. 2ENTER.gif (Note: the subscript is contextually determined. The chemical calculator, as would be the case with any other calculator, will not tell you if you have written the correct formula for calcium hydroxide!)

Click on the Enter button to place the molar mass of calcium hydroxide in the calculation workspace.

2ENTER2.gif

Mole Conversion Calculations

We can complete the calculation by multiplying the two terms:

2MULT.gif (Note: the setup displays the chemical formula, not the molar mass that was used in the calculation. This makes it a lot easier to check your setup. The current program does not calculate the number of significant figures that should be displayed in the answer.)

It is possible, however, to reset the precision of the display. Here, I've set it to 2.) 2MULT2.gif

Using the Formula Mode

Molar Mass Calculations: Another source of error students may encounter in working this problem involves the calculation of the molar mass from a chemical formula. More help is available to the student needing review the steps involved in this calculation can be obtained by opening up the Formula Mode.

Like to try another problem? Return to Sample Problems.