2
Explain
Thinking in Parts Per Million
Duration
45 minutes
Type
Explain
Standards
MS-PS1-1, 6.RP.A.3
Learning Objectives
Students will be able to:
- Define concentration and explain why it matters
- Convert between percentages, fractions, and ppm
- Use ppm to describe gas concentrations in air
- Calculate ppm given real-world scenarios
What is Concentration?
Concentration describes how much of one substance is mixed in another.
Everyday Examples:
- Salt in soup (too little = bland, too much = inedible)
- Chlorine in pool water
- Caffeine in coffee
- Pollution in air
Understanding Scale
| Unit | Meaning | Example |
|---|---|---|
| Percentage (%) | Parts per 100 | Oxygen at 21% |
| Parts per million (ppm) | Parts per 1,000,000 | CO2 at 420 ppm |
| Parts per billion (ppb) | Parts per 1,000,000,000 | Some pollutants |
The Key Conversion
1% = 10,000 ppm
% to ppm:
ppm = percentage × 10,000
ppm to %:
percentage = ppm ÷ 10,000
Practice Problems
Convert to ppm:
- Oxygen is 21% of air. How many ppm? 21 × 10,000 = 210,000 ppm
- Argon is 0.93% of air. How many ppm? 0.93 × 10,000 = 9,300 ppm
- CO2 is 0.042% of air. How many ppm? 0.042 × 10,000 = 420 ppm
Convert to percentage:
- Indoor CO2 is 1,000 ppm. What percentage? 1,000 ÷ 10,000 = 0.1%
- CO safety limit is 35 ppm. What percentage? 35 ÷ 10,000 = 0.0035%
What Does 1 ppm Look Like?
Imagine finding one grain of rice in a million grains. That's 1 ppm!
1 ppm is like:
- 1 inch in 16 miles
- 1 second in 11.5 days
- 1 cent in $10,000
Scaling up:
- 10 ppm = 1 in 100,000
- 100 ppm = 1 in 10,000
- 1,000 ppm = 0.1%
Why ppm Matters: Indoor CO2
| CO2 Level | ppm | Effect |
|---|---|---|
| Outdoor air | ~420 | Normal |
| Well-ventilated room | 600-800 | Good |
| Crowded room | 1,000-2,000 | Drowsiness begins |
| Poor ventilation | >2,500 | Headaches, poor concentration |
Even though all these are less than 1%, the differences matter significantly for health and learning!