What is the mole fraction?
List each component of a mixture or solution with its amount in moles, or with its mass and molar mass. The calculator gives the mole fraction and mole percent of every component and the total moles.
- Mole fraction of the first component
- X = 0.243715
The mole fraction of Ethylene glycol is 0.243715.
- X (first component)
- 0.243715
- Mole percent (first component)
- 24.3715
- Every component
- Ethylene glycol: 0.243715 (24.3715%); Water: 0.756285 (75.6285%)
- Moles of each
- Ethylene glycol: 35.7661 mol; Water: 110.988 mol
- Total moles
- 146.754
- First component
- Ethylene glycol
Mole fraction of the first component: X = 0.243715. The mole fraction of Ethylene glycol is 0.243715.
How to calculate
Finds the mole fraction and mole percent of each component of a mixture or solution from its moles, or from its mass and molar mass: X = moles of the component ÷ total moles.
Example with the default inputs (Components [Name Ethylene glycol, Mass (g) 2,220, Molar mass (g/mol) 62.07; Name Water, Mass (g) 2,000, Molar mass (g/mol) 18.02]): The mole fraction of Ethylene glycol is 0.243715.
Method: X_A = n_A ÷ (n_A + n_B + …), where each n is typed in moles or is mass (g) ÷ molar mass (g/mol); mole percent = 100 × X.
- Every component of the mixture is listed; the fractions add up to 1.
- A row with moles uses them; a row without moles needs both its mass and its molar mass.
Worked examples
Each example is checked against the calculator on every build.
- Components Ethylene glycol 2220 62.07; Water 2000 18.02 gives X (first component) 0.243715, Mole fraction of the first component X = 0.243715.Source: OpenStax, Chemistry 2e, §11.4 Colligative Properties (mole fraction X_A = mol A ÷ total mol of all components), https://openstax.org/books/chemistry-2e/pages/11-4-colligative-properties, Example 11.3 (a): X(ethylene glycol) = 0.244
- Components Ammonia 0.85 17.03; Water 125 18.02 gives X (first component) 0.007144.Source: OpenStax, Chemistry 2e, §11.4 Colligative Properties (mole fraction X_A = mol A ÷ total mol of all components), https://openstax.org/books/chemistry-2e/pages/11-4-colligative-properties, Check Your Learning after Example 11.3: X(NH₃) = 7.14 × 10⁻³
- Components Ethanol 4; Glycerin 1 gives X (first component) 0.8, Every component Ethanol: 0.8 (80%); Glycerin: 0.2 (20%), Total moles 5.Source: OpenStax, Chemistry 2e, §11.4 Colligative Properties (mole fraction X_A = mol A ÷ total mol of all components), https://openstax.org/books/chemistry-2e/pages/11-4-colligative-properties, Example 11.6: 4.000 mol ethanol and 1.00 mol glycerin, X(ethanol) = 0.800
- Components Oxygen 2.83; Nitrous oxide 8.41 gives X (first component) 0.251779, Mole percent (first component) 25.177936.Source: OpenStax, Chemistry 2e, §9.3 Stoichiometry of Gaseous Substances, Mixtures, and Reactions (X_A = n_A ÷ n_Total), https://openstax.org/books/chemistry-2e/pages/9-3-stoichiometry-of-gaseous-substances-mixtures-and-reactions, Example 9.15: X(O₂) = 2.83 ÷ 11.24 = 0.252
How it works
Formula. For components A, B, C, …:
X_A = n_A ÷ (n_A + n_B + n_C + …)
and mole percent = 100 × X.
Moles of each row. A row with moles typed uses them. A row with the moles box empty uses n = mass (g) ÷ molar mass (g/mol), and then needs both. Moles are from 10⁻¹⁵ to 10¹², grams from 10⁻¹² to 10¹², and molar masses from 10⁻⁶ to 10⁶ g/mol. A mixture has 2 to 10 rows.
Results. The headline is the mole fraction of the first row; every component’s mole fraction and mole percent, and its moles, are listed in row order. Typed values are exact decimals, so each fraction is exact until it is rounded once, to 6 significant figures with trailing zeros dropped (0.0071439). A value below 0.000001 is written with a power of ten, in the lists as in the number rows (1 × 10⁻²⁷); the total moles row also writes 10¹⁵ or more that way. A row with no name is called “component 1”, “component 2”, and so on; a name loses the spaces at its ends.
Worked examples by hand
Antifreeze (OpenStax Example 11.3). Ethylene glycol: 2,220 g ÷ 62.07 g/mol = 35.7661 mol. Water: 2,000 g ÷ 18.02 g/mol = 110.988 mol. X(glycol) = 35.7661 ÷ 146.754 = 0.243715 (OpenStax: 0.244).
Ammonia in water (Check Your Learning). 0.850 ÷ 17.03 = 0.0499119 mol NH₃; 125 ÷ 18.02 = 6.93674 mol water. X(NH₃) = 0.0499119 ÷ 6.98665 = 0.0071439 (OpenStax: 7.14 × 10⁻³).
Ethanol and glycerin (Example 11.6). 4 mol and 1 mol: X(ethanol) = 4 ÷ 5 = 0.8, X(glycerin) = 0.2.
Anesthetic gas (OpenStax Example 9.15). 2.83 mol O₂ and 8.41 mol N₂O: X(O₂) = 2.83 ÷ 11.24 = 0.251779 (25.1779 mol %).
Other questions people ask
How do I calculate the mole fraction?
Divide the moles of one component by the moles of all the components together: X_A = n_A ÷ n_total. In a solution of 35.77 mol ethylene glycol and 110.99 mol water, X(glycol) = 35.77 ÷ 146.75 = 0.2437.
What is mole percent?
The mole fraction times 100. A mole fraction of 0.2518 is 25.18 mol %: about a quarter of the molecules in the mixture belong to that component.
How do I get moles from grams?
Divide the mass by the molar mass: 2,220 g of ethylene glycol ÷ 62.07 g/mol = 35.77 mol. Leave the moles box empty and type the mass and molar mass, and the page does this for that row.
Do the mole fractions add up to 1?
Yes, when every component is listed: the fractions of all the components add up to exactly 1, and the mole percents to 100%. A missing component makes the others too large.
How is mole fraction different from molarity and molality?
Mole fraction compares moles with moles, so it has no units. Molarity divides the moles of solute by the volume of solution (mol/L), and molality by the mass of solvent (mol/kg).
What is the mole fraction used for?
Dalton’s law gives a gas’s partial pressure as its mole fraction times the total pressure, and Raoult’s law gives a solution’s vapor pressure as the solvent’s mole fraction times the pure solvent’s vapor pressure: 0.800 × 0.178 atm = 0.142 atm for ethanol with glycerin.