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Lessons · Neutralization

When acid meets base: which one runs out?

Machine-checked — balanced, charge-conserved, extent-verified by ChemKernel 3 modeling assumptions (disclosed)

20.0 mL of 0.100 M HCl(aq) is mixed with 30.0 mL of 0.0500 M NaOH(aq). The acid's H+ and the base's OH- combine into water, leaving dissolved sodium chloride. How much water forms, which reactant runs out first, and what stays in solution?

Mass of H2O\mathrm{H_{2}O} formed
0.027 g
Salt formed (NaCl\mathrm{NaCl})
0.088 g
Limiting reagent
NaOH
Left in solution
HCl 0.5 mmol
Molecular equation — what you combine
HCl (aq)+NaOH (aq)→NaCl (aq)+H2O (l)\mathrm{HCl}\,\text{(aq)} + \mathrm{NaOH}\,\text{(aq)} \rightarrow \mathrm{NaCl}\,\text{(aq)} + \mathrm{H_{2}O}\,\text{(l)}
Complete ionic — every strong electrolyte shown as free ions strong-electrolyte model
H++Cl−+Na++OH−→Na++Cl−+H2O\mathrm{H}^{+} + \mathrm{Cl}^{-} + \mathrm{Na}^{+} + \mathrm{OH}^{-} \rightarrow \mathrm{Na}^{+} + \mathrm{Cl}^{-} + \mathrm{H_{2}O}
Net ionic — spectators cancelled, the reaction that actually happens
H++OH−→H2O\mathrm{H}^{+} + \mathrm{OH}^{-} \rightarrow \mathrm{H_{2}O}

Spectator ions (unchanged, still dissolved): Cl⁻ Na⁺

Verification Every claim below was proven at build time — not asserted.
  • ✓ Atoms balance across the equation [conservation matrix]
  • ✓ Charge balances (net ionic re-verified) [charge row]
  • ✓ Units cancel through the dimensional chain [units engine]
  • ✓ No amount goes negative — extent is physical [nonnegative-extent guard]
✗ Common misconception: “Neutralization uses up both the acid and the base completely.”

Only when the amounts match the ratio exactly. Here one reactant runs out first and the other is left over: NaOH reaches 0 (all 1.5 mmol consumed), but HCl keeps 0.5 mmol unreacted — so both are not used up. Neutralization stops when the limiting reactant hits 0; whatever the other started with above the matching amount stays in solution.

Modeling assumptions — author-asserted, disclosed not discharged
  • model HCl and NaOH are strong and dissociate completely in water.
  • model The neutralization goes essentially to completion (H+ + OH- -> water).
  • model Solution volumes are additive.

Concepts in this lesson

Linked into the Chemical Atlas where an entry exists; the rest fill in as the Atlas grows.

Practice this

The lesson goes deep on one scenario; the gym builds fluency by repetition. Drill these: