Molar Concentration
What is Molar Concentration?
Molar concentration (molarity) is the number of moles of dissolved substance per liter of solution.
Basic Formula:
c = n / V
c: concentration (mol/L) | n: amount (mol) | V: volume (L)
c = n / V
c: concentration (mol/L) | n: amount (mol) | V: volume (L)
Unit: mol/L (Molar, M)
Rearrangements:
- n = c · V (amount from concentration)
- V = n / c (volume from concentration)
Example: 2 mol NaCl in 500 mL water → c = 2/0.5 = 4 mol/L
Formulas
Concentration:
c = n / V
c = n / V
Amount of Substance:
n = c · V
n = c · V
Volume:
V = n / c
V = n / c
Molar Mass:
M = m / n
M = m / n
Practical Examples
Example 1: Concentration of a NaCl Solution
You dissolve 58.5 g NaCl in 1 L of water.
M(NaCl) = 58.5 g/mol
n = 58.5 / 58.5 = 1 mol
c = 1 mol / 1 L = 1 mol/L
You dissolve 58.5 g NaCl in 1 L of water.
M(NaCl) = 58.5 g/mol
n = 58.5 / 58.5 = 1 mol
c = 1 mol / 1 L = 1 mol/L
Example 2: Required Amount of Substance
You want to prepare 500 mL of a 0.1 mol/L solution.
V = 0.5 L
n = 0.1 mol/L × 0.5 L = 0.05 mol
(That's 0.05 × 98 = 4.9 g H₂SO₄)
You want to prepare 500 mL of a 0.1 mol/L solution.
V = 0.5 L
n = 0.1 mol/L × 0.5 L = 0.05 mol
(That's 0.05 × 98 = 4.9 g H₂SO₄)
Example 3: Volume Calculation
You have 2 mol HCl and want a 0.5 mol/L solution.
V = 2 mol / 0.5 mol/L = 4 L
You have 2 mol HCl and want a 0.5 mol/L solution.
V = 2 mol / 0.5 mol/L = 4 L
Technical Background
Important Notes:
- The volume is always the total volume of the solution, not just the solvent!
- Molar concentration is one of the standardized units in laboratory chemistry
- Typical concentrations: 0.01–0.1 mol/L (dilute), 0.1–1 mol/L (normal), > 1 mol/L (concentrated)
- Concentrated acids/bases can reach 10–18 mol/L
Practical Applications:
- Laboratory Chemistry: Precise dosing of reagents
- Analytics: Standardization and calibration
- Pharmacy: Medication dosing
- Industry: Quality control and reproducibility
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