How do you convert percentage concentration to molarity?
To convert percentage concentration to molarity, you need to know the density of the solution and the molecular weight of the solute. The process involves several steps:
- Calculate the mass of solute in a given volume of solution.
- Convert the mass of solute to moles.
- Calculate the volume of the solution in liters.
- Divide the number of moles by the volume in liters to get molarity.
Suppose you have a 25% (w/w) solution of sodium hydroxide (NaOH) with a density of 1.28 g/mL. To convert this to molarity:
- For 100 g of solution, there are 25 g of NaOH.
- The molecular weight of NaOH is 40 g/mol.
- Moles of NaOH = 25 g ÷ 40 g/mol = 0.625 mol
- Volume of solution = 100 g ÷ 1.28 g/mL = 78.125 mL = 0.078125 L
- Molarity = 0.625 mol ÷ 0.078125 L = 8 M
A 25% (w/w) solution of NaOH with a density of 1.28 g/mL is equivalent to an 8 M solution.
Converting percentage concentration to molarity is a common task in chemistry. Percentage concentration represents the mass of solute per 100 units of solution, while molarity expresses the number of moles of solute per liter of solution.
Percentage Concentration to Molarity Conversion Chart
| Percentage Concentration (w/w) | Density (g/mL) | Molecular Weight (g/mol) | Molarity (M) |
|---|---|---|---|
| 5% | 1.05 | 58.44 (NaCl) | 0.90 |
| 10% | 1.10 | 58.44 (NaCl) | 1.88 |
| 15% | 1.15 | 58.44 (NaCl) | 2.95 |
| 20% | 1.20 | 58.44 (NaCl) | 4.11 |
| 25% | 1.25 | 58.44 (NaCl) | 5.35 |
| 30% | 1.30 | 58.44 (NaCl) | 6.68 |
| 35% | 1.35 | 58.44 (NaCl) | 8.10 |
| 40% | 1.40 | 58.44 (NaCl) | 9.59 |
Note: This chart uses sodium chloride (NaCl) as an example solute. The density values are approximate and may vary in real solutions.
Percent Concentration to Molarity Formula
The formula to convert percent concentration to molarity is:
M = (ρ × w% × 10) ÷ MWWhere:
- M is molarity (mol/L)
- ρ (rho) is the density of the solution (g/mL)
- w% is the weight percentage of the solute
- 10 is a conversion factor (1000 mL/L ÷ 100%)
- MW is the molecular weight of the solute (g/mol)
Convert 12% (w/w) sulfuric acid (H2SO4) solution with a density of 1.08 g/mL to molarity.
- ρ = 1.08 g/mL
- w% = 12
- MW of H2SO4 = 98.08 g/mol
M = (1.08 × 12 × 10) ÷ 98.08 = 1.32 M
Convert 45% (w/w) potassium hydroxide (KOH) solution with a density of 1.45 g/mL to molarity.
- ρ = 1.45 g/mL
- w% = 45
- MW of KOH = 56.11 g/mol
M = (1.45 × 45 × 10) ÷ 56.11 = 11.63 M