Multi-Step Conversions

  Sometimes, there will be cases where you will be given information that you would have to use in order to make numerous conversions. Here are some examples:

EXAMPLE:

12.5 grams of Hydrogen (H2) are placed in a balloon at STP (Standard Temperature and Pressure = 0º C & 101.3 kPa). Determine it's volume.

1. First, use molar mass as your conversion factor and cancel accordingly.

-> 12.5 g of H2    x    1 mol     
                               2.0 g*


*The mass in grams is 2.0 because there are hydrogen is diatomic.

2. Next, use molar volume as your conversion factor and cancel accordingly.

-> 12.5 g of H2    x    1 mol    x    22.4 L
                               2.0 g           1 mol

3. Alter your answer to have the appropriate number of significant digits.

-> There are 1.4 x 10² Liters in 12.5 grams of Hydrogen.


   There will be other instances where they ask you for more conversions such as grams to atoms or liters to molecules. The most important thing to do is to first recognize what you have and what your answer's units should be. From there, you can decide on you conversion factors. Here are some of them:

Molar Volume (of all gases @ STP):
22.4 L / 1 mol

Molar Volume (of all gases @ SATP-> Standard Ambient Temperature & Pressure):
24.8 L / 1 mol


Molar Mass:
grams (g) / 1 mol


Avogadro's Number:

6.02 x 10²³ molecules or atoms or fundamental units / 1 mol

  Here are some links to help you out as well:
http://www.youtube.com/watch?v=tS9l-OxucQU
http://www.youtube.com/watch?v=AsqEkF7hcII&feature=related
http://www.youtube.com/watch?v=8TkY36qB1f0