Chemistry 2e · Solutions and Colloids

Electrolytes

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Why this matters
The college version
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In 30 seconds

An is a substance whose aqueous solution conducts electricity. Pure water conducts almost nothing; when certain solutes dissolve, they release ions — charged particles that can drift through the solution and carry current. The more ions a solution contains, the better it conducts.

Electrolytes come in three classes, defined by how completely they produce ions:

Strong electrolytes ionize essentially completely (≈100%): soluble ionic compounds (e.g., NaCl), strong acids (e.g., HCl, HNO₃), and strong bases (e.g., NaOH, KOH).
Weak electrolytes ionize only partially, establishing an equilibrium: weak acids (e.g., CH₃COOH), weak bases (e.g., NH₃), and a few salts (e.g., HgCl₂, Pb(CH₃COO)₂).
Nonelectrolytes produce no ions at all: molecular solutes like sugar, ethanol, and urea. Their solutions do not conduct.

The distinction is about degree of , not concentration — a dilute still ionizes completely, while a concentrated still ionizes only a little. This topic's equations also set up the van't Hoff factor (i), which quantifies how many particles each formula unit contributes — the link to colligative properties (topic 4).

Why this matters

The body runs on electrolytes: Nerve impulses and muscle contraction depend on Na⁺, K⁺, Ca²⁺, and Mg²⁺ gradients across cell membranes. Oral rehydration solutions and IV fluids are, at heart, carefully balanced electrolyte solutions; severe imbalance (from diarrhea, vomiting, or dehydration) can be dangerous.
Electrical safety and technology: of solutions matters in batteries, electroplating, and water-quality testing (e.g., measuring total dissolved solids in drinking water).
Medicine and pharmacy: Whether a drug is a salt (electrolyte) or a neutral molecule () determines its solubility, absorption, and behavior in the body.
Exam foundation: Classifying substances as strong/weak/nonelectrolytes and writing their dissociation equations is a classic general-chemistry skill that feeds directly into acids/bases, solubility, and colligative properties.

The college version

Core Concepts

Strong electrolytes: complete ionization

Three families:

Soluble ionic compounds: NaCl(s) → Na+(aq) + Cl-(aq). The ions pre-exist in the crystal; water simply separates them.
Strong acids: HCl(aq) + H₂O(l) → H₃O+(aq) + Cl-(aq) — essentially no HCl molecules remain. The common strong acids: HCl, HBr, HI, HNO₃, H₂SO₄ (first proton), HClO₄.
Strong bases: NaOH(s) → Na+(aq) + OH-(aq). Group 1 metal hydroxides and the heavier group 2 hydroxides (e.g., Ba(OH)₂).

Strong electrolyte solutions conduct well because nearly every formula unit contributes ions. Use → (single arrow) in their equations.

Weak electrolytes: partial ionization with equilibrium

Weak acids and bases ionize only a few percent, so the solution contains mostly intact molecules plus a small ion population — conductivity is poor but measurable.

$CH 3 COOH(aq) + H 2 O(l) ⇌ H 3 O+(aq) + CH 3 COO-(aq)$

$NH 3 (aq) + H 2 O(l) ⇌ NH 4 +(aq) + OH-(aq)$

Use ⇌ (equilibrium arrows) and describe with K_a or K_b. Note that "weak" refers to the extent of ionization, not the concentration: 0.1 M acetic acid is a weak electrolyte even though the solution may feel strong.

Nonelectrolytes: no ions

Molecular compounds that do not ionize in water — sugar (C₁₂H₂₂O₁₁), ethanol (C₂H₅OH), urea — dissolve as neutral molecules. No charged species, no conductivity. Water itself, though it autoionizes slightly, conducts so little that pure water is effectively a nonelectrolyte.

Conductivity as a diagnostic

A simple circuit test — two electrodes, a bulb (or ammeter), and the solution — sorts the classes:

Bright bulb / large current → strong electrolyte (many ions).
Dim bulb / small current → weak electrolyte (few ions).
No light / no current → nonelectrolyte.

The same measurement, done quantitatively, gives the van't Hoff factor: for a strong electrolyte like NaCl, i = 2 (two ions per formula unit); for CaCl₂, i = 3. Measured values fall slightly below ideal because ions pair up at higher concentrations. This factor multiplies concentrations in all colligative-property calculations (topic 4).

General lab safety principles

Conductivity and electrolyte experiments often involve acids, bases, and salts. General principles: wear eye protection, handle concentrated reagents carefully, never taste or directly touch samples, and dispose of solutions as directed by your instructor. None of the classification chemistry requires unsafe procedures.

How It Works / Step-by-Step Process

Worked example 1: classifying and writing equations

Problem. Classify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte, and write the equation describing its behavior in water: (a) KNO₃, (b) HF, (c) C₁₂H₂₂O₁₁ (sugar), (d) Ba(OH)₂.

Solution.

(a) KNO₃ — soluble ionic compound → strong electrolyte: $KNO 3 (s) \to K+(aq) + NO 3 -(aq)$
(b) HF — a weak acid → weak electrolyte: $HF(aq) + H 2 O(l) ⇌ H 3 O+(aq) + F-(aq)$
(c) Sugar — covalent, non-ionizing → nonelectrolyte: dissolves as intact C₁₂H₂₂O₁₁(aq) molecules.
(d) Ba(OH)₂ — group 2 hydroxide → strong electrolyte: $Ba(OH) 2 (s) \to Ba 2+ (aq) + 2OH-(aq)$ Note the stoichiometry: each formula unit yields three ions → i = 3.

Worked example 2: predicting relative conductivity

Problem. Rank these 0.1 M solutions by expected conductivity: NaCl, CH₃COOH, C₆H₁₂O₆ (glucose), CaCl₂.

Solution.

Count ions per formula unit at full ionization: NaCl → 2; CaCl₂ → 3; CH₃COOH → far fewer than 2 (only a few percent ionize); glucose → 0.
Rank by ion concentration: CaCl₂ > NaCl >> CH₃COOH > glucose. CaCl₂ gives three ions per formula unit; NaCl two; acetic acid only a tiny fraction of ions; glucose none.
Lesson: conductivity tracks number of ions in solution, which depends on both the formula (i) and the degree of ionization.

Worked example 3: using the van't Hoff factor

Problem. A solution is 0.050 M in CaCl₂. Assuming complete ionization, what is the total concentration of dissolved particles? What would the measured i tell you if it came out as 2.7?

Solution.

Write the dissociation: CaCl₂ → Ca²⁺ + 2Cl⁻ → i = 3.
Total particle concentration = i × M: $[particles] = 3 \times 0.050 M = 0.15 M$ Dimensional check: (unitless)(mol/L) = mol/L ✓
A measured i of 2.7 (below 3) means some ion pairing or incomplete separation of ions at this concentration — real solutions deviate slightly from the ideal; this matters when computing colligative properties precisely (topic 4).

Common Confusions

Do Not Confuse	With	Difference
"Strong" electrolyte	"Concentrated" solution	Strong = complete ionization; a 0.001 M HCl is still a strong electrolyte, and a 6 M acetic acid is still weak
Weak electrolyte	Nonelectrolyte	Weak electrolytes produce some ions (dim bulb); nonelectrolytes produce none (no bulb)
Soluble	Electrolyte	Solubility is about dissolving; conductivity is about ionizing. Sugar is very soluble but a nonelectrolyte
Molecular compound	Nonelectrolyte	Not always: strong acids like HCl are molecular yet strong electrolytes; classification depends on ionization, not bond type alone
Equilibrium arrow	Single arrow	Weak electrolytes need ⇌ (equilibrium); strong electrolytes use → (complete)
One ion per formula unit	Ions per formula unit	Count ALL ions: CaCl₂ gives 3 particles, Na₂SO₄ gives 3, NaCl gives 2 — the factor i matters for colligative properties

Eli explains

The same idea, in plain words

Explain it like I’m 10

Think of ions as tiny charged runners in water. Salt water has lots of runners (ions), so electricity can race through it — that's a strong electrolyte. Vinegar has only a few runners, so electricity crawls through slowly — a weak electrolyte. Sugar water has no runners at all — the electricity just stops, like a road with no one to pass the ball. Your body needs these runners to send messages between your brain and your muscles.

Key takeaways

Electrolyte = solute whose solution conducts electricity by releasing ions; classification = degree of ionization, not concentration.
Strong electrolytes (≈100% ionized): soluble ionic compounds, strong acids (HCl, HNO₃, H₂SO₄ first proton, HClO₄, HBr, HI), strong bases (group 1 hydroxides, Ba(OH)₂) — single arrow.
Weak electrolytes (partial): weak acids (CH₃COOH, HF, HCN), weak bases (NH₃) — equilibrium arrows, K_a/K_b.
Nonelectrolytes: molecular solutes with no ions (sugar, ethanol, urea) — no conductivity.
Conductivity test: bright = strong, dim = weak, none = nonelectrolyte.
Van't Hoff factor i: ions per formula unit (NaCl → 2, CaCl₂ → 3); needed for colligative properties.
Body function depends on electrolyte balance: Na⁺, K⁺, Ca²⁺, Mg²⁺ gradients drive nerves and muscles; rehydration solutions restore them.
General safety: eye protection and careful handling for all acid/base/salt work.

Check yourself

5 review questions from the chapter. Try each one, then open the answer.

Define strong, weak, and nonelectrolytes in terms of ionization.
Show answer
Strong: ionize essentially completely; weak: ionize only partially (equilibrium); nonelectrolytes: produce no ions.
Write the equation for HNO₃ in water. Strong or weak?
Show answer
HNO₃(aq) + H₂O(l) → H₃O+(aq) + NO₃-(aq) — strong acid, strong electrolyte (single arrow).
Why does a 0.1 M sugar solution not conduct electricity?
Show answer
Sugar dissolves as intact neutral molecules — no ions, so no charge carriers to conduct.
What is the van't Hoff factor for Na₂SO₄? For CH₃COOH (ideal)?
Show answer
Na₂SO₄: 3 (2 Na⁺ + 1 SO₄²⁻). Acetic acid: ideal i = 1 (it barely ionizes; treat as ~1).
Give one biological reason electrolyte balance matters.
Show answer
Na⁺/K⁺/Ca²⁺/Mg²⁺ gradients across cell membranes drive nerve impulses and muscle contraction; imbalance disrupts these essential functions (which is why rehydration solutions replace them).

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Study tools & related lessonsKey vocabulary · Related

Key vocabulary

electrolyte: Substance whose solution conducts electricity via ions
strong electrolyte: Ionizes ~100% in water
weak electrolyte: Ionizes only partially (equilibrium)
nonelectrolyte: Dissolves as neutral molecules; no ions
ionization: Formation of ions from a dissolved substance
van't Hoff factor (i): Number of particles a formula unit produces
conductivity: Ability of a solution to carry electric current

Sources & references

openstax.org — Chemistry 2e

This lesson was adapted from the open educational references above; their licenses and attributions are preserved. See Copyright & Licensing.

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In 30 seconds

Why this matters

The college version

Core Concepts

Strong electrolytes: complete ionization

Weak electrolytes: partial ionization with equilibrium

Nonelectrolytes: no ions

Conductivity as a diagnostic

General lab safety principles

How It Works / Step-by-Step Process

Worked example 1: classifying and writing equations

Worked example 2: predicting relative conductivity

Worked example 3: using the van't Hoff factor

Common Confusions

The same idea, in plain words

Key takeaways

Check yourself

Keep learning

Key vocabulary

Related lessons

Sources & references