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General Chemistry I · Core Concept

Properties of Aqueous Solutions

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On this page 7 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Study tools

In 30 seconds

A is a homogeneous mixture of a (the dissolved substance) and a (the dissolving medium). In an , water is the solvent. When an ionic compound dissolves, polar water molecules surround and separate the ions in a process called . Substances whose solutions conduct electricity are electrolytes; strong electrolytes fully dissociate, weak electrolytes partially ionize, and nonelectrolytes form no ions.

Why this matters

balance is a core concern in medicine. Intravenous fluids such as 0.9% saline (NaCl) and lactated Ringer's solution contain strong electrolytes — Na+, K+, Ca2+, Cl−, and lactate — because these ions control nerve signaling, muscle contraction, and fluid distribution. Blood tests report "electrolytes" precisely because these dissolved ions (not intact salts) are what cells actually use.

The college version

1. Solutes, Solvents, and Solutions

A solution is a homogeneous mixture — the same composition and properties throughout. The solute is the component in the smaller amount (or the one that changes phase); the solvent is the component in the larger amount. In an aqueous solution, water is the solvent and the dissolved material is the solute. In seawater, for example, water is the solvent and the many dissolved salts are the solutes.

2. Hydration — How Water Dissolves Things

Water is a polar molecule: oxygen pulls shared electrons toward itself, making the oxygen end partially negative (δ−) and the hydrogen ends partially positive (δ+). When an ionic solid such as NaCl enters water, the δ− oxygens orient toward Na+ cations and the δ+ hydrogens toward Cl− anions. This cumulative attraction overcomes the ionic lattice energy, so the ions separate and become surrounded by water — this is hydration. Water also dissolves polar covalent molecules (sugar, ethanol) through similar dipole attractions or hydrogen bonding, but it does not pull them into ions.

3. Electrolytes: Strong, Weak, and Nonelectrolytes

An electrolyte is any substance whose aqueous solution conducts electricity; conduction requires mobile, charged particles (ions).

  • : dissociates or ionizes essentially 100%. All soluble ionic compounds (NaCl, KBr, CaCl2), strong acids (HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4), and strong bases (NaOH, KOH, Ca(OH)2) are strong electrolytes.
  • : ionizes only slightly, existing mostly as intact molecules with a small fraction of ions. Weak acids (acetic acid, HC2H3O2) and weak bases (ammonia, NH3) are weak electrolytes.
  • : dissolves as intact molecules and forms no ions, so the solution does not conduct. Sugar (C12H22O11), ethanol (C2H5OH), and urea are nonelectrolytes.

How it works

  1. A polar solute or ionic solid is placed in water.
  2. Water molecules collide with and orient around the solute particles.
  3. For ionic compounds, water's attractions overcome the crystal lattice, freeing each ion.
  4. Each freed ion is surrounded by a shell of oriented water molecules (hydration).
  5. The result is a homogeneous solution of hydrated ions, which conducts electricity.
  6. For molecular compounds, the molecules disperse but stay intact (nonelectrolyte) or ionize only slightly (weak electrolyte).

Common confusions

Do not confuseWithDifference
Strong electrolyteConcentrated solutionStrong = fully ionized; concentrated = a lot of solute present
Weak electrolyteNonelectrolyteWeak electrolytes make a few ions; nonelectrolytes make none
Strong acidStrong electrolyteStrong acids are one class of strong electrolyte; strong bases and soluble salts are the others
DissolvingReactingDissolving is a physical change (solute recoverable); a reaction makes new substances
HydrationHydrolysisHydration is physical solvation; hydrolysis is a chemical reaction with water

Memory aids

"Salts and strong acids/bases light the bulb; sugars stay dark." Remember "SUGAR won't conduct" (Sucrose, Urea, Glucose, Alcohol, and other covalent solutes form no ions).

Quick review

Topic Recap

Aqueous solutions are homogeneous mixtures of a solute in water. Water's polarity lets it hydrate (solvate) ions and polar molecules. Whether a solution conducts depends on whether it contains ions: strong electrolytes ionize fully, weak electrolytes partially, and nonelectrolytes not at all. This vocabulary is the foundation for ionic equations and solution stoichiometry.

Knowledge Check

  1. In a glass of salt water, which component is the solvent?
  2. Which end of a water molecule surrounds a sodium cation (Na+), and why?
  3. Classify each as strong electrolyte, weak electrolyte, or nonelectrolyte: HCl, sucrose, NH3, KNO3.
  4. How many moles of ions does one mole of AlCl3 produce when it dissolves?
  5. Does a dilute solution of a strong electrolyte still conduct electricity? Explain.

Answers and Rationales

  1. Water — it is present in the larger amount and is the dissolving medium.
  2. The oxygen (δ−) end, because opposite charges attract and Na+ is positive.
  3. HCl is a strong electrolyte (strong acid), sucrose is a nonelectrolyte (molecular, no ions), NH3 is a weak electrolyte (weak base), and KNO3 is a strong electrolyte (soluble ionic salt).
  4. Four moles: Al3+ + 3 Cl− (1 + 3 = 4).
  5. Yes — strength describes how completely the solute ionizes, so even a dilute strong electrolyte is fully dissociated and conducts, just with fewer ions present.
Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Imagine a crowd of tiny, lopsided magnets called water molecules. Each has a slightly negative end (the oxygen) and a slightly positive end (the hydrogens). Drop table salt into water, and the negative oxygen ends tug on the positive sodium ions while the positive hydrogen ends tug on the negative chloride ions. Repeated billions of times, this tug-of-war pulls the crystal apart and wraps each ion in a snug coat of water. That wrapping is hydration.

A useful comparison is melting versus dissolving. Melting uses heat to overcome the attractions holding a solid together; dissolving uses the attraction between solvent and solute to do the same job without high temperature. This comparison stops being exact because in melting a pure substance stays the same substance (ice becomes water), while dissolving makes a new mixture and, with salt, tears the solute into charged pieces (ions) that were not free to move before.

Simple Example

Stir a spoonful of sodium chloride (NaCl) into water. The solid disappears and the water now conducts electricity: NaCl(s) H2O⟶ Na+(aq) + Cl-(aq) The "(aq)" label means each ion is hydrated — surrounded by water and free to wander through the solution.

Worked example

Dissociation equations show how many ions form per formula unit, bridging to the concentration work in later topics.

Example: calcium chloride dissociates into three ions per formula unit: CaCl2(s) → Ca2+(aq) + 2 Cl-(aq) One mole of CaCl2 therefore produces three moles of ions (1 mol Ca2+ + 2 mol Cl−).

Example: one mole of Na2SO4 gives three moles of ions: Na2SO4(s) → 2 Na+(aq) + SO42-(aq) Common setup error: forgetting the subscript's coefficient. The "2" before Na+ (and Cl− above) comes from the formula subscript — it is a coefficient in the products, never a subscript edit.

Key takeaways

  • High yield: Strong electrolytes dissociate ~100%; strength is about how completely a substance ionizes, not how concentrated it is.
  • High yield: All soluble ionic compounds are strong electrolytes; strong acids and strong bases are too.
  • High yield: Weak acids and weak bases are weak electrolytes; they exist mostly as intact molecules.
  • Molecular compounds such as sugar and ethanol are nonelectrolytes.
  • "Strong" means degree of ionization; "concentrated/dilute" means amount of solute — a weak acid can be concentrated and a strong acid can be dilute.

Keep learning

Ready to build on this? Continue to the next lesson.

Practice General Chemistry I

This lesson has no separate scored set. Practice draws from the subject’s question bank.

Study tools & related lessonsYou’ll learn to · Key vocabulary · Related

You’ll learn to

  • Identify the solute and solvent in a solution, and describe what makes a solution "aqueous."
  • Explain the process of hydration and why water dissolves ionic and polar covalent substances.
  • Distinguish strong electrolytes, weak electrolytes, and nonelectrolytes, and classify common substances.
  • Predict the ions produced when an ionic compound or a strong acid dissolves in water.

Key vocabulary

Solution
A homogeneous mixture of two or more substances
Solute
The substance dissolved (usually the smaller amount)
Solvent
The dissolving medium (usually the larger amount)
Aqueous solution
A solution in which water is the solvent
Hydration
Water molecules surrounding dissolved ions/molecules
Electrolyte
A substance whose solution conducts electricity via ions
Strong electrolyte
Dissociates ~100% into ions
Weak electrolyte
Ionizes only slightly
Nonelectrolyte
Dissolves without forming ions
Dissociation
Separation of an ionic compound into ions in solution

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