Mass of Solute in a Solution of Known Molarity

General Chemistry • Chemical Reactions

Written by STEM Calculators Team Published October 17, 2025 Updated February 24, 2026

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Calculating the Mass of Solute in a Solution of Known Molarity

If you know a solution’s molarity \(M\) (mol·L⁻¹), the solution volume \(V\) (in liters), and the solute’s molar mass \(M_m\) (g·mol⁻¹), the solute mass is \( m = M \times V \times M_m \).

Workflow

Write the solute formula correctly (use parentheses when needed).
Compute the molar mass by summing atomic masses: \(M_m=\sum_i \nu_i\,Ar_i\).
Convert volume to liters (mL → L by dividing by 1000).
Find moles: \(n = M \times V\).
Convert to mass: \(m = n \times M_m\).

Worked Example

Problem: What mass of NaCl is present in 250.0 mL of 0.750 M NaCl solution?

Step 1: Molar mass from the formula.

\[ \begin{aligned} M_{\text{NaCl}} &= \sum_i \nu_i\,Ar_i \\ &= 1\cdot Ar_{\text{Na}} + 1\cdot Ar_{\text{Cl}} \\ &= 1\cdot 22.990 + 1\cdot 35.45 \\ &= 58.44\ \mathrm{g\ mol^{-1}} \end{aligned} \]

Step 2: Convert molarity and volume to moles.

\[ \begin{aligned} n &= M\,V \\ &= (0.750\ \mathrm{mol\ L^{-1}})\,(0.2500\ \mathrm{L}) \\ &= 0.18750\ \mathrm{mol} \end{aligned} \]

Step 3: Convert moles to mass.

\[ \begin{aligned} m &= n\,M_m \\ &= (0.18750\ \mathrm{mol})\,(58.44\ \mathrm{g\ mol^{-1}}) \\ &= 10.97\ \mathrm{g} \end{aligned} \]

Tips & Guardrails

Use mL or L for volume; the calculator converts mL → L automatically.
Formulas can include parentheses and numeric subscripts. State symbols (s, l, g, aq) are ignored.
Charges/electrons are out of scope here (no free polyatomic ions, no half-reactions).
Report a sensible number of significant figures; this tool lets you choose 3–6 s.f.

Frequently Asked Questions

What formula relates molarity to the mass of solute in a solution?

First find moles with n = M x V, where V is in liters, then convert to mass with m = n x Mm. Combining gives m = M x V x Mm.

Why does the calculator convert mL to liters before computing mass?

Molarity is defined as mol/L, so the volume must be in liters for units to match. The conversion is V(L) = V(mL) / 1000.

How does the calculator determine the molar mass from the solute formula?

It sums atomic masses according to the subscripts in the formula, including any atoms inside parentheses. The result is the molar mass Mm in g/mol.

Can I enter ions with charges or redox half-reactions in this tool?

No. Charges, electrons, and half-reactions are not supported because the calculator is designed for neutral chemical formulas used to compute molar mass and solution stoichiometry.

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Frequently Asked Questions

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