How do I calculate g of solute in a given volume of solution using the percent concentration?

You can also treat this as a simple unit conversion problem and solve it with the five step plan for converting units:

1. Identify the unknown, including units. You want to find grams of alcohol.
2. Choose a starting point. You have two pieces of information: the volume of the solution, and its concentration. "g alcohol" is not a fraction, so your starting point shouldn't be a fraction either. 5% (w/v) alcohol means 5 g alcohol per 100 mL of solution- it should be used as a conversion factor but not as a starting point. Your strategy is

   1.0 L solution

   g alcohol

3. List the connecting conversion factors. Conversion factor are stepping stones that connect the starting point and the unknown. The concentration connects a volume of solution with a mass of alcohol:

   1.0 L solution

   mL solution

   100 mL solution = 5 g alcohol

   g alcohol

4. Multiply the starting measurement by conversion factors.

   1.0 L solution

   (

   1000 mL solution 1 L solution

   )

   (

   5 g alcohol 100 mL solution

   )

   = 50 g alcohol

5. Check the result: does the answer make sense? Don't forget this step!

Author: Fred Senese senese@antoine.frostburg.edu