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E3.2 · Explain formation of ionic, molecular, and non-polar solutions

Learn to explain formation of ionic, molecular, and non-polar solutions through clear examples and targeted practice.

Ontario Grade 11 Chemistry

Solutions and Solubility

Ontario Grade 11 Chemistry — Study topic E3.2

Salt disappears when stirred into water, but the salt has not vanished. Its particles have spread through the water. Sugar can also dissolve, yet its particles do not become ions. Oil and water, by contrast, separate into visible layers. These observations can be explained by looking at the kinds of particles in each substance and how those particles interact. This lesson focuses on how ionic, molecular, and non-polar solutions form.

What you will learn

Describe a solution as a uniform mixture of particles.
Explain how water particles separate and surround ions when an ionic substance dissolves.
Distinguish molecular solutes that remain as molecules from ionic solutes that form separated ions.
Use particle attraction and polarity to explain why some substances mix to form solutions.

1. Start with mixtures and particle attractions

A solution is a uniform mixture. Its particles are spread evenly through the mixture, so a small sample has the same overall composition as another sample. The substance that does the dissolving is the solvent. The substance that dissolves is the solute. In salt water, water is the solvent and salt is the solute.

A particle model helps explain what happens. In a solid, particles are close together. When a solute dissolves, particles separate from one another and become mixed among solvent particles. The particles do not need to disappear or change into a different substance for a solution to form.

The particles in matter attract one another. A solution forms when attractions between solute and solvent particles can help separate the solute particles and keep them mixed. A useful course-level guide is “like dissolves like”: substances with similar kinds of particle attractions are more likely to form a solution. This is a guide, not a promise that every pair of similar substances will mix in every amount.

Polarity describes an uneven distribution of electrical charge in a molecule. A polar molecule has a slightly positive region and a slightly negative region. Water is polar. A non-polar molecule has no strongly separated positive and negative regions. Many oils are non-polar. Ions are charged particles: positive ions are cations, and negative ions are anions.

Solvent dissolves solute; together they can form a uniform solution.
Dissolving spreads particles through a solvent; it does not always change their identity.
Polarity and particle attractions help predict whether substances form a solution.

2. Formation of an ionic solution

When an ionic solid such as sodium chloride is added to water, the solid may seem to disappear. At the particle level, it is made of positive and negative ions held together in a repeating arrangement. Water molecules are polar: the oxygen side is slightly negative, and the hydrogen sides are slightly positive.

Water particles attract the ions at the surface of the solid. The oxygen side of a water molecule is attracted to positive ions. The hydrogen sides are attracted to negative ions. Water particles surround the separated ions and help keep them spread through the liquid. This surrounding is called hydration. It does not mean that the ions have changed into water or become neutral.

The dissolved sodium and chloride ions remain charged and can move through the solution. The formula unit of sodium chloride separates into one sodium ion and one chloride ion. The balanced symbolic representation shows the same number of each kind of atom and the same total charge on both sides.

Use the solubility table provided for the course when deciding whether an ionic compound is expected to dissolve in water. Do not assume that every ionic solid is soluble. If an ionic substance does not dissolve appreciably, it will not form a uniform solution under the stated conditions.

\mathrm{NaCl(s) \rightarrow Na^+(aq) + Cl^-(aq)}

Water’s partial charges attract oppositely charged ions.
Dissolved ions remain ions; they are separated and surrounded by water molecules.
A dissolution equation must conserve atoms and total charge.

3. Formation of a molecular solution

Molecular substances are made of molecules. Some molecular substances, such as sugar, dissolve in water. When sugar dissolves, sugar molecules separate from one another and spread among water molecules. The molecules remain molecules. They do not split into positive and negative ions just because they dissolve.

For a molecular solute to mix with a solvent, attractions between solute and solvent particles must make mixing possible. Polar molecular substances are more likely to mix with polar solvents such as water. The exact result depends on the substance; polarity is a guide rather than a rule that guarantees solubility.

A molecular formula can identify the particles present, but it does not by itself show whether a substance dissolves. For a molecular solute that remains intact, the dissolved particles are still molecules. The label (aq) means the substance is dissolved in water; it does not mean that it has become ionic.

\mathrm{C_{12}H_{22}O_{11}(s) \rightarrow C_{12}H_{22}O_{11}(aq)}

A molecular solute can dissolve while remaining as whole molecules.
An aqueous molecular substance is not automatically an ionic substance.
Particle attractions and polarity help explain whether a molecular solute mixes with a solvent.

4. Formation of a non-polar solution

A non-polar solution forms when non-polar solute particles mix with a non-polar solvent. For example, a non-polar substance may dissolve in a non-polar liquid because the particles can mix without creating a large mismatch in their attractions. The particles spread through one another, making a uniform mixture.

Oil and water usually separate into layers. Water is polar, while many oils are non-polar. Their particles do not attract one another in a way that allows them to remain evenly mixed. Shaking can temporarily break one liquid into small droplets in the other, but the droplets join again and the layers return. A temporary cloudy mixture of droplets is not the same as a stable, uniform solution.

Use the “like dissolves like” guide carefully: polar substances tend to dissolve in polar solvents, and non-polar substances tend to dissolve in non-polar solvents. The guide helps explain patterns, but observations or course reference information are needed for a specific substance pair.

Non-polar solutes tend to form solutions with non-polar solvents.
Oil and water separate because their particles do not remain evenly mixed.
A temporarily cloudy mixture is not necessarily a solution.

Worked example

Predicting what happens when three solutes meet water

Use the particle model to explain what happens when sodium chloride, sugar, and a non-polar oil are each added separately to water. Identify whether the dissolved particles are ions or molecules, where a solution is expected, and what particle attractions support the prediction.

Classify the solutes
Sodium chloride is ionic, sugar is molecular, and the oil is non-polar. Water is a polar molecular solvent. This classification identifies the particles and helps compare their attractions with water.
Predict the ionic case
If the solubility table indicates that sodium chloride dissolves, water surrounds the separated sodium and chloride ions. The dissolved particles are ions, not intact sodium chloride formula units.
$\mathrm{NaCl(s) \rightarrow Na^+(aq) + Cl^-(aq)}$
Predict the molecular case
Sugar molecules can separate from one another and spread through water. The dissolved particles remain sugar molecules; they are not represented as ions.
$\mathrm{C_{12}H_{22}O_{11}(s) \rightarrow C_{12}H_{22}O_{11}(aq)}$
Predict the non-polar case
The oil is non-polar and water is polar, so the “like dissolves like” guide predicts that the oil will not form a uniform solution with water. It is expected to separate rather than remain evenly spread through the water.

Answer: Sodium chloride forms an ionic solution when it dissolves, with separated hydrated ions. Sugar can form a molecular solution, with intact sugar molecules. The non-polar oil is expected to separate from polar water rather than form a uniform solution.

Check: The particle types match the representations: sodium chloride gives charged ions, sugar remains neutral molecules, and the oil-water pair is not expected to remain uniformly mixed.

Common mistakes and how to avoid them

Saying that an ionic substance disappears when it dissolves.

Correction: Its ions separate and spread through the solvent. They remain present in the solution.

Writing dissolved sugar as separate positive and negative ions.

Correction: Sugar is molecular, and its particles remain whole sugar molecules when dissolved.

Assuming that every substance labelled (aq) is ionic.

Correction: The label (aq) means dissolved in water. An aqueous substance can contain ions or intact molecules.

Calling any shaken mixture a solution.

Correction: A solution is uniform. Oil and water may look mixed briefly after shaking but separate into layers.

Lesson summary

A solution is a uniform mixture of solute and solvent particles.
In an ionic solution, water surrounds separated ions; the ions keep their charges.
A molecular solute can dissolve as intact molecules.
Non-polar solutes tend to dissolve in non-polar solvents, while polar substances tend to mix with polar solvents.
“Like dissolves like” is a useful guide, and course solubility information helps with specific substances.

Check your understanding

Question 1

When sodium chloride dissolves in water, what particles are spread through the solution?

Separate sodium and chloride ions
Intact neutral sodium chloride molecules only
Sodium atoms and chlorine atoms
Water molecules changed into sodium and chloride

Show answer and explanation

Separate sodium and chloride ions

An ionic solid that dissolves separates into ions. Water surrounds those ions, which remain charged.

Question 2

A molecular solute dissolves in water and remains molecular. Which statement describes its particles?

They remain whole molecules among water molecules.
They must become positive and negative ions.
They change into atoms before mixing.
They cease to exist in the solution.

Show answer and explanation

They remain whole molecules among water molecules.

Some molecular solutes dissolve as intact molecules. Dissolving does not always split a solute into ions.

Question 3

Why do oil and water usually separate after shaking?

The polar water and non-polar oil do not remain evenly mixed.
Water turns the oil into ions.
Oil particles are always larger than water particles.
The oil dissolves completely, then sinks as a solid.

Show answer and explanation

The polar water and non-polar oil do not remain evenly mixed.

Water is polar and many oils are non-polar. Their particles do not remain uniformly mixed, so the liquids separate into layers.

Key terms

Solution: A uniform mixture in which solute particles are spread through a solvent.
Solvent: The substance that dissolves another substance to form a solution.
Solute: The substance that dissolves in a solvent.
Ion: A charged particle. A cation is positive; an anion is negative.
Polar molecule: A molecule with slightly positive and negative regions because its charge is unevenly distributed.
Non-polar molecule: A molecule without strongly separated positive and negative regions.
Hydration: The surrounding of dissolved ions by water molecules.

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Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 11 Chemistry (SCH3U), expectation E3.2. It is a study resource, not an official curriculum publication.

Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.

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