What is a solution?

How is the concentration of a solution calculated?

Parts Per Million and Parts Per Billion

What is a solution?

How is the concentration of a solution calculated?

Learning Target 3.3.1: I can explain the dynamic process by which a solution is formed when one or more solute dissolve in a solvent. I can calculate solution concentration in terms of molarity, percent concentration, and parts per million.

Parts Per Million and Parts Per Billion

Goal 3.3.1.f: I can calculate solution concentration in terms of parts per million and parts per billion.

Your teacher found the tap water at your school has 400 parts per billion (ppb) of fluorine in it. Turn to your neighbor and talk about what you think this means. t might be helpful to draw a picture.

There are many solutions where the concentration is tiny. So tiny those molarities would be similar to 0.00000001 M, which is annoying to write and use. Instead, we use parts per million (ppm) and parts per billion (ppb), which are other forms of percent mass.

Here are the formulas to determine the concentration in ppm and ppb:

You should notice that ppm and ppb are very similar to percent mass from above. Percent mass is really out of 100 g of solution (that is why we multiply by 100% in the percent mass equation), but ppm is out of 1 million grams and ppb is out of 1 billion grams of solution.

To imagine the small scale of these concentrations, draw the beakers below and then place one dot (to represent 1 gram of solute) in each of the beakers.

The following is another way of describing the difference between the three beakers.

• 1% NaCl means 1 g NaCl in 100 g of solution.
• 1 ppm NaCl means 1 g NaCl in 1,000,000 g of solution.
• 1 ppb NaCl means 1 g NaCl in 1,000,000,000 g of solution

When determining ppm and ppb, make sure the units for mass of solute and solution are in grams (if not, you will need to convert), and the mass of solution is the total mass of the solute and solvent.

Practice:

14. 0.68 grams of mercury (Hg) is accidentally spilled into a small aquarium containing 1,000 g of water. What is the concentration of Hg in ppm?

 15. In a nearby lake, it is found that 0.008 grams of oxygen is dissolved in 1,000 mL of water. What is the concentration in ppb?

16. Determine the concentration in ppm of a solution made by dissolving 8.50 g of Mg(NO3)2 in 70.0 g of water.

Check your answers to the Concentration Practice Problems Answers.

For additional practice problems do the Worksheet 3.3.9, Solutions Problems. Your teacher may want to use this as homework for this unit.

Check your answers to 3.3.9 Solutions Problems Homework here.

Solutions: Parts Per Million and Parts Per Billion by MN Partnership for Collaborative Curriculum is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. CC-BY-NC