Chemical Reactions in Solutions (molarity)

General Chemistry • Chemical Reactions

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

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Solute formula

Mass of solute (g)

Leave blank if you provide moles.

Moles of solute (mol)

If both mass and moles are provided, moles take priority.

Solution volume

Volume must be > 0.

Display precision

Used only for display; exact arithmetic is used internally.

How to enter:
• Use element symbols and parentheses. Subscripts may be normal numbers or real subscripts (e.g., H2SO4 or H₂SO₄).
• Optional state symbols (s), (l), (g), (aq) are allowed and ignored.
• Charges/electrons are not supported (no polyatomic-charge notation or half-reactions).

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Molarity of a Solution

Molarity (c, often denoted M) is the amount of solute in moles per liter of solution. To compute it from a weighed mass, you also need the solute’s molar mass.

Definitions

From the chemical formula, the molar mass is the sum of atomic masses:

\[ M_{\text{solute}}=\sum_i \nu_i\,Ar_i \quad (\mathrm{g\,mol^{-1}}) \]

Convert mass to moles, then use molarity:

\[ n=\frac{m}{M_{\text{solute}}}\qquad\text{and}\qquad c=\frac{n}{V}=\frac{n}{V_{\mathrm{(L)}}}\quad(\mathrm{mol\,L^{-1}}) \]

Convert volume to liters when entered in mL:

\[ V_{\mathrm{(L)}}=\frac{V_{\mathrm{(mL)}}}{1000} \]

Workflow

Write the solute formula (e.g., NaCl, H₂SO₄).
Compute molar mass \(M\) from atomic masses.
Use either:
- Given mass \(m\): \(n=m/M\).
- Given moles \(n\): use directly.
Convert volume to liters if needed: \(V_{\mathrm{(L)}} = V_{\mathrm{(mL)}}/1000\).
Compute molarity: \(c=n/V_{\mathrm{(L)}}\).

Example

NaCl solution: 5.844 g NaCl in 0.500 L.

\[ \begin{aligned} M_{\mathrm{NaCl}} &= Ar(\mathrm{Na}) + Ar(\mathrm{Cl}) \\ &= 22.99 + 35.45 \approx 58.44\ \mathrm{g\,mol^{-1}} \\ n &= \frac{m}{M} = \frac{5.844}{58.44} \approx 0.1000\ \mathrm{mol} \\ c &= \frac{n}{V} = \frac{0.1000}{0.500} = 0.2000\ \mathrm{mol\,L^{-1}} \end{aligned} \]

Good practice

Enter formulas with parentheses and subscripts; the calculator accepts normal digits or true subscripts.
Use a reasonable number of significant figures (the tool displays 3–6; default is 4).
Ignore optional state symbols; charges/electrons are not supported.

Frequently Asked Questions

What is molarity and what does M mean in chemistry?

Molarity is the amount of solute per liter of solution, with units mol/L. The symbol M is often used to denote molarity, but it is different from molar mass.

How does the calculator find molarity from mass and volume?

It computes molar mass from the formula, converts grams to moles with n = m / M, converts volume to liters if needed, then calculates c = n / V(L).

Why must volume be in liters for molarity calculations?

Molarity is defined as moles per liter, so any volume entered in mL must be converted using V(L) = V(mL) / 1000 to keep units consistent.

What happens if I enter both mass and moles of solute?

The calculator uses the moles input and ignores the mass for the stoichiometric amount, since moles are already the required amount unit for molarity.

Does changing significant figures change the calculation result?

No. Significant figures only control how many digits are displayed; the tool uses exact arithmetic internally and then formats the final numbers for display.

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Frequently Asked Questions

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