Calculate solution strength and how to dilute properly
Solution Concentration
Concentration tells you how much solute (the dissolved substance) is in a given volume of solution. Common formats: Percentage: 5% means 5 g of solute per 100 mL of solution. Ratio: 1:1000 means 1 g per 1,000 mL. mg/mL: milligrams of solute per milliliter of solution.
Percentage Concentrations
How much salt is in 500 mL of a 0.9% saline solution?
0.9% means 0.9 g per 100 mL
Set up: 0.9/100 = x/500
x = 4.5 g of salt
Dilution Formula
C₁ × V₁ = C₂ × V₂
C₁ = starting concentration, V₁ = starting volume
C₂ = final concentration, V₂ = final volume
The amount of solute stays the same — you're just adding more liquid.
Dilute 100 mL of 10% solution to 2%. What is the final volume?
10 × 100 = 2 × V₂
1,000 = 2V₂
V₂ = 500 mL total
Add 400 mL of water to the 100 mL
💡 Key idea: Diluting makes the concentration smaller and the volume larger, but the total amount of solute doesn't change.
🎯 Practice Problems
1. How many grams of glucose are in 250 mL of a 5% glucose solution?
A) 5 g
B) 12.5 g
C) 25 g
D) 50 g
2. A 1:1000 solution means 1 g per 1,000 mL. How many mg per mL?
A) 0.001 mg/mL
B) 0.1 mg/mL
C) 1 mg/mL
D) 10 mg/mL
3. You have 200 mL of 15% solution. You need to dilute to 5%. What total volume?
A) 300 mL
B) 400 mL
C) 600 mL
D) 1,000 mL
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🎯 Bonus Practice
1. How much water do you add to 50 mL of 20% solution to make 10%?
A) 25 mL
B) 50 mL
C) 100 mL
D) 150 mL
2. A cleaning solution calls for a 1:10 dilution. How much concentrate for 5 liters total?
A) 0.5 L
B) 1 L
C) 0.05 L
D) 5 L
3. What is the concentration of 3 g dissolved in 200 mL, expressed as a percentage?
A) 0.15%
B) 1.5%
C) 3%
D) 15%
4. You mix 100 mL of 8% solution with 100 mL of 2% solution. What is the final concentration?
A) 3%
B) 4%
C) 5%
D) 10%
5. A 0.9% saline bag contains 1,000 mL. How many grams of salt?