Chemistry • Year 11 • Module 1 • Lesson 12
Solubility and Like-Dissolves-Like
Lock in the core vocabulary, the “like dissolves like” principle, and the IMF-based framework for predicting solubility before tackling harder questions.
1. Term–definition match
The definitions below are shuffled. In the right-hand column write the matching term from this list: solubility, like dissolves like, miscible, immiscible, hydrophilic, hydrophobic, hydration shell, amphiphilic, ion-dipole force, lattice energy. 10 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | The maximum mass of solute that dissolves in a given volume of solvent at a specific temperature, forming a stable homogeneous solution. | |
| 1.2 | The principle that polar solvents dissolve polar and ionic solutes, and non-polar solvents dissolve non-polar solutes, because IMF compatibility between solute and solvent determines dissolution. | |
| 1.3 | Describes two liquids that mix in any proportion to form a homogeneous solution because their intermolecular forces are compatible (e.g. ethanol and water). | |
| 1.4 | Describes two liquids that do not mix but form two distinct layers because their IMFs are incompatible (e.g. oil and water). | |
| 1.5 | “Water-loving” — describes substances or molecular regions that are polar or ionic and interact favourably with water via H-bonding or ion-dipole forces. | |
| 1.6 | “Water-fearing” — describes non-polar substances or molecular regions that do not interact favourably with water and are excluded from aqueous solutions. | |
| 1.7 | The layer of polar water molecules that surrounds and stabilises an ion in aqueous solution, oriented with δ− oxygen toward cations and δ+ hydrogen toward anions. | |
| 1.8 | A molecule that has both a polar (hydrophilic) head group and a non-polar (hydrophobic) tail; examples include soaps, detergents, and phospholipids. | |
| 1.9 | The attractive force between an ion (carrying a full charge) and a polar molecule’s permanent dipole; the primary force responsible for dissolving ionic compounds in water. | |
| 1.10 | The energy required to separate the ions in one mole of an ionic solid, overcoming the electrostatic attractions that hold the crystal lattice together. |
2. True or false — with correction
Circle T or F for each statement. If the statement is false, write the corrected version on the line below it. 12 marks (1 T/F + 1 correction each)
2.1 All ionic compounds dissolve in water because water is polar and can form ion-dipole forces with all ions. T / F
2.2 Iodine (I2) dissolves better in hexane than in water because I2 is non-polar and hexane is non-polar, so their dispersion forces are compatible. T / F
2.3 CO2 dissolves well in water because it has two polar C=O bonds, making it a polar molecule overall. T / F
2.4 Vegetable oil does not dissolve in water because oil molecules have no intermolecular forces at all. T / F
2.5 Ethanol is miscible with water because its –OH group can form hydrogen bonds with water molecules. T / F
2.6 A substance described as “insoluble” in water has absolutely no interaction with water molecules at all. T / F
3. Fill-in-the-blank paragraph
Use the word bank to complete the passage. Each word is used once. 8 marks (1 per blank)
Word bank:
compatible · dispersion · hydration · hydrophobic · immiscible · ion-dipole · lattice · polar
The guiding principle “like dissolves like” means that dissolution occurs when the intermolecular forces of the solute and solvent are ___________ in type. Water is a strongly ___________ solvent that dissolves ionic compounds through ___________ forces, in which δ− oxygen atoms orient toward cations and δ+ hydrogen atoms orient toward anions. For an ionic compound to dissolve, the energy released when water molecules form the ___________ shell around each ion must exceed the ___________ energy of the crystal. Non-polar molecules such as hydrocarbons interact only through weak ___________ forces, making them ___________ — excluded from the water network. Water and hexane are therefore ___________: they form two distinct layers rather than a single homogeneous solution.
4. Function recall
Answer each question in 1–2 sentences using precise chemistry terms. 8 marks (2 each)
4.1 What is the function of the water’s dipole in dissolving an ionic compound such as NaCl?
4.2 Why does the addition of soap allow grease to be washed away with water?
4.3 What role does lattice energy play in determining whether an ionic compound dissolves in water?
4.4 Why are multiple –OH groups in glucose responsible for its high solubility in water?
5. Build a concept map
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a linking phrase (e.g. “requires”, “explains”, “is determined by”). Aim for at least 6 labelled arrows. 6 marks (1 per valid labelled arrow)
Supplied terms: like dissolves like · IMF compatibility · polar solvent · ionic compound · hydrophobic effect · miscibility.
Q1 — Term–definition match
1.1 solubility • 1.2 like dissolves like • 1.3 miscible • 1.4 immiscible • 1.5 hydrophilic • 1.6 hydrophobic • 1.7 hydration shell • 1.8 amphiphilic • 1.9 ion-dipole force • 1.10 lattice energy.
Q2 — True / false with correction
2.1 False. Not all ionic compounds dissolve in water. Solubility depends on the balance between lattice energy and hydration energy. Compounds with very high lattice energy (e.g. AgCl, BaSO4, CaCO3) are insoluble despite water’s polarity.
2.2 True.
2.3 False. CO2 is a non-polar molecule overall. Although it has two polar C=O bonds, its linear, symmetric geometry (O=C=O) means the two dipoles point in opposite directions and cancel exactly — giving a net dipole of zero. CO2 is therefore only sparingly soluble in water.
2.4 False. Oil molecules do have intermolecular forces — dispersion forces. The reason oil does not dissolve in water is that oil’s dispersion forces are incompatible with water’s strong hydrogen-bond network. Dissolving oil would require breaking H-bonds in water with no comparable energy released from oil–water interactions.
2.5 True.
2.6 False. Even “insoluble” substances interact weakly with water through dispersion forces. The correct statement is that the solute–solvent interactions are insufficient to compensate for the disruption of water’s hydrogen-bond network, so dissolution does not occur to any significant extent.
Q3 — Cloze paragraph
In order: compatible / polar / ion-dipole / hydration / lattice / dispersion / hydrophobic / immiscible.
Q4.1 — Water’s dipole function
The permanent dipole of water means the oxygen atom carries a partial negative charge (δ−) and each hydrogen carries a partial positive charge (δ+). When NaCl approaches water, the δ− oxygen atoms orient toward Na&sup+; ions and the δ+ hydrogen atoms orient toward Cl− ions. These ion-dipole forces are strong enough to overcome the interionic attractions in the NaCl lattice, pulling the ions from the surface and stabilising them in solution as hydrated ions.
Q4.2 — Function of soap
Soap molecules are amphiphilic: they have a long non-polar (hydrophobic) hydrocarbon tail and a polar (hydrophilic) ionic head. The non-polar tails dissolve in the grease through dispersion forces, while the polar heads remain in the water. The soap molecules form spherical micelles around grease particles, with tails pointing inward and heads pointing outward into water. This allows grease to be dispersed (emulsified) into the water and rinsed away.
Q4.3 — Role of lattice energy
Lattice energy is the energy required to separate the ions in one mole of an ionic solid. For dissolution to occur, the hydration energy released when water molecules surround the separated ions must be greater than or equal to the lattice energy. If the lattice energy is very high (e.g. BaSO4), even the strong ion-dipole interactions of water cannot compensate, so the compound remains insoluble.
Q4.4 — Role of –OH groups in glucose
Each –OH group in glucose can act as both a hydrogen-bond donor (O–H···O) and a hydrogen-bond acceptor (O···H–O) with surrounding water molecules. Glucose has five –OH groups plus a ring oxygen, allowing it to form numerous hydrogen bonds with water simultaneously. The total energy released by forming these H-bonds more than compensates for breaking the water–water H-bonds needed to accommodate the glucose molecule, making glucose highly soluble in water.
Q5 — Sample concept map
Correct maps should include arrows such as:
- like dissolves like — is based on → IMF compatibility
- IMF compatibility — determines → miscibility
- polar solvent — dissolves → ionic compound
- polar solvent — causes → hydrophobic effect
- ionic compound — is hydrophilic so it → like dissolves like
- hydrophobic effect — results in → immiscibility (not miscibility)
Award 1 mark per valid labelled arrow (minimum 6, maximum 6 marked).