Concentration of Solutions
A solution is made when a solute (e.g. salt) dissolves in a solvent (e.g. water). The concentration tells us how much solute is dissolved in a certain volume of solvent.
What is concentration?
- Concentration is a measure of how much solute is dissolved in a given volume of solution
- It is usually measured in g/dm³ (grams per decimetre cubed)
Concentration formula
To calculate concentration, use the following triangle to help:
m = mass (g)
C = concentration (g/dm³)
V = volume (dm³)
Formulas
- Concentration = mass ÷ volume
- Mass = concentration × volume
- Volume = mass ÷ concentration
💡 1 dm³ = 1000 cm³ (so divide cm³ by 1000 to convert to dm³)
Example 1: Calculate concentration
Question:
What is the concentration of a solution made by dissolving 10 g of salt in 0.25 dm³ of water?
Answer:
Concentration = 10 ÷ 0.25 = 40 g/dm³
Example 2: Calculate mass of solute
Question:
How much solute is in 200 cm³ of solution with a concentration of 15 g/dm³?
Step 1: Convert 200 cm³ to dm³ → 200 ÷ 1000 = 0.2 dm³
Step 2: Mass = concentration × volume = 15 × 0.2 = 3 g
Example 3: Calculate volume
Question:
How much solution is needed to dissolve 5 g of solute at a concentration of 10 g/dm³?
Answer:
Volume = 5 ÷ 10 = 0.5 dm³ (or 500 cm³)
Why concentration matters
- Tells us how strong or dilute a solution is
- Used in titrations, reactions, and medicine
- Needed for accurate quantitative chemistry calculations
Questions
- What is concentration a measure of?
- What is the unit for concentration?
- Convert 250 cm³ into dm³
- What is the concentration of 5 g of salt in 0.5 dm³ of solution?
- How do you calculate mass from concentration and volume?
Summary
- Concentration = mass of solute ÷ volume of solution
- Measured in g/dm³
- Convert cm³ to dm³ by dividing by 1000
- Use the formula triangle to calculate mass, volume, or concentration
- Higher concentration = more solute in the same volume