Molarity Calculator
Molarity Formulas
Common Molar Masses
Related Calculators
Understanding Molarity
What is Molarity?
Molarity (M) is a measure of concentration that tells you how many moles of solute are dissolved in one liter of solution. It's one of the most common ways to express concentration in chemistry.
Molarity Formula
Key Relationships
Moles
Moles = Molarity × Volume (L)
Volume
Volume (L) = Moles ÷ Molarity
Mass
Mass (g) = Moles × Molar Mass
The Dilution Equation
Stock concentration × Stock volume = Final concentration × Final volume
This equation is used when diluting a concentrated solution. The total amount of solute (moles) remains constant—you're just adding more solvent to spread it out.
Example Problems
Example 1: Finding Molarity
Q: You dissolve 5.84 g of NaCl (MM = 58.44 g/mol) in 500 mL of water. What's the molarity?
A: n = 5.84 ÷ 58.44 = 0.1 mol; M = 0.1 ÷ 0.5 = 0.2 M
Example 2: Dilution
Q: How do you make 1 L of 0.1 M HCl from 12 M stock?
A: V₁ = (0.1 × 1000) ÷ 12 = 8.33 mL of stock + water to 1 L
Common Molarity Values
| Solution | Molarity | Common Use |
|---|---|---|
| Saline (0.9%) | 0.154 M | Medical/IV solutions |
| Conc. HCl | 12 M | Lab stock solution |
| Conc. H₂SO₄ | 18 M | Lab stock solution |
| Conc. NaOH | ~19 M | Lab stock solution |
Safety Tips
- Always add acid to water, never water to acid (prevents splashing)
- Concentrated acids and bases are corrosive—wear appropriate PPE
- Label all solutions with concentration, date, and preparer's initials
- Use volumetric flasks for accurate dilutions
Frequently Asked Questions
What is molarity and how do I calculate it?
Molarity (M) is concentration expressed as moles of solute per liter of solution. Formula: M = moles / liters. To find moles, divide mass by molar mass: n = mass / MM. For example, 5.85g NaCl (MM=58.5) in 1L water = 0.1M solution.
How do I use the dilution formula C1V1 = C2V2?
This formula helps calculate dilutions. C1 and V1 are initial concentration and volume; C2 and V2 are final values. To make 500mL of 0.5M solution from 2M stock: V1 = (0.5 x 500) / 2 = 125mL stock + 375mL water.
What is the difference between molarity and molality?
Molarity (M) is moles per liter of solution. Molality (m) is moles per kilogram of solvent. Molality is temperature-independent and preferred for precise work, while molarity is more practical for everyday lab use.
Why do I add acid to water, not water to acid?
Adding acid to water is safer because water absorbs heat generated by dilution. Adding water to concentrated acid can cause violent boiling and spattering. Remember: 'Do as you oughta, add acid to water.'