What concentration means
Concentration compares how much solute is present to how much solution there is. A concentrated solution has more solute particles in the same volume than a dilute solution.
Unit 3: Intermolecular Forces and Properties
Molarity and Solution Concentration
How do chemists describe how much solute is dissolved in a solution?
24 min
High School Chemistry / AP Chemistry
5 source chapters
Learning Objectives
- Define molarity as moles of solute per liter of solution.
- Calculate molarity from moles and volume.
- Rearrange M = n / V to solve for moles or volume.
- Explain why solution volume, not solvent volume alone, is used in molarity.
- Interpret concentration at the particle level.
Molarity as a ratio
Molarity is a ratio: moles of solute divided by liters of solution. The denominator is total solution volume because the final mixture is what particles occupy.
Same solute, different volume
Imagine the same number of dissolved particles spread through two beakers. In the smaller volume, particles are closer together, so the concentration is higher.
Two beakers with equal solute particles but different solution volumes.
Molarity equation
Use liters of solution in the denominator. Convert milliliters to liters before substituting.
M = n / V
- 1M is molarity in mol/L, often written as M.
Worked Example
Calculate molarity
What is the molarity of a solution containing 0.500 mol NaCl in 2.00 L of solution?
Quick Check
Two solutions contain the same moles of solute. Which one is more concentrated?
Quick Check
How many moles of solute are in 0.750 L of a 0.200 M solution?
Misconception Check
Misconception: Molarity is grams of solute divided by water volume.
Correction: Molarity uses moles of solute divided by liters of final solution. If grams are given, convert grams to moles first.
Key Terms
solution
溶液A homogeneous mixture of solute and solvent.
solute
溶质The substance dissolved in a solution.
solvent
溶剂The substance that dissolves the solute.
molarity
物质的量浓度Moles of solute per liter of solution.
concentration
浓度How much solute is present in a given amount of solution.
dilution
稀释Adding solvent to lower concentration while solute amount stays the same.
Summary
- Molarity is moles of solute per liter of solution.
- Use liters in M = n / V.
- The final solution volume is the denominator.
- Higher molarity means more solute particles per liter.
Practice bridge
Convert 250. mL to liters, then calculate the molarity of 0.100 mol KBr in that volume.
Explain your answer using both the equation and a particle-level picture.
Related Resources
Marker chapters
- Chemistry 11e By Steven Zumdahl, DeCoste/Chapter 11- Properties of Solutions
- Chemistry 14e by Raymond Chang Jason Overby/Chapter 04 - Reactions in Aqueous Solutions
- Chemistry 14e by Raymond Chang Jason Overby/Chapter 12 - Physical Properties of Solutions
- Chemistry The Central Science in SI Units 15th Global Edition/Chapter 13- Properties of Solutions
- Chemistry 11e By Steven Zumdahl, DeCoste/Chapter 4- Types of Chemical Reactions and Solution Stoichiometry
Optional downloads
- molarity_solution_concentration_student_handout.md
- molarity_solution_concentration_teacher_guide.md
- molarity_solution_concentration_qa_report.md
Practice Bridge
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