When two solutions contain the same solute, their solute moles add. Enter each molarity and measured volume, plus that solute’s molar mass, to calculate the combined amount and molarity under an additive-volume assumption.

Formula: total mol = A mol/L × A mL ÷ 1,000 + B mol/L × B mL ÷ 1,000; combined mol/L = total mol ÷ ((A mL + B mL) ÷ 1,000); g = total mol × molar mass

Worked example

Mix 100 mL at 1 mol/L with 300 mL at 0.5 mol/L of the same solute. The total is 0.25 mol in an assumed 400 mL final volume, or 0.625 mol/L. At 58.44 g/mol, it contains 14.61 g solute.

Both solutions must contain the same solute

This is an inventory calculation for one chemical identity. Different solutes cannot be collapsed into one molarity. OpenStax defines molarity as moles of a solute per liter of solution; each starting amount follows concentration times volume.

Volumes are assumed additive

The displayed final volume is A volume plus B volume. Real mixtures may contract, expand, react or precipitate. If an accurate final volume is measured and differs from that sum, this simple estimate is not suitable.

Concentration is not a mixing instruction

The page does not evaluate compatibility, heat of mixing, purity or a preparation procedure. It only combines entered quantities. Zero molarity is valid for a solute-free solution; both volume inputs must still be positive.

Explore the related calculation

For a different starting point, try the molarity calculator or return to the main calculator. Browse the complete tool directory for this site.

Reference and corrections

The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.

openstax.org reference

Found a problem? Email contact@gramstomoles.org.

Mix two solutions molarity calculator

Enter your values

Result