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Solutions
Chemistry
Useful for: OSSC RHT — Regular High School Teacher, OSEPA Upper Primary — Science, OSSC Science, OSSSC Govt TGT Science — CBZ, OSSSC Govt TGT Science — PCM, SSB Lecturer (Degree Colleges), SSB TGT CBZ, SSB TGT PCM
Overview
A solution is a homogeneous mixture of solute and solvent; its concentration and properties depend on the amount of solute.
Key points
- Molarity = moles of solute per litre of solution; molality = moles per kilogram of solvent.
- Saturated solutions hold the maximum solute at a temperature.
- Solubility of gases decreases as temperature rises; Henry’s law links gas solubility to pressure.
- Colligative properties depend on the number of solute particles: boiling-point elevation, freezing-point depression, osmotic pressure.
- Colloids scatter light (Tyndall effect); true solutions do not.
- Suspensions settle; solutions do not.
Explanation
- Molality does not change with temperature; molarity does.
- Salt on icy roads lowers the freezing point.
- Reverse osmosis purifies water.
- Soda water fizzes when opened as pressure drops.
- Milk and fog are colloids.
Step by step
- Identify the concept, method or fact asked.
- Recall the definition, thinker, year or rule.
- Apply it and eliminate extreme or mismatched options.
Examples
- 2 moles in 1 litre → 2 M solution.
- Fish struggle in warm water → less dissolved oxygen.
- A torch beam visible in fog → Tyndall effect.
Traps and advanced points
- Trap: Mixing molarity and molality.
- Trap: Thinking gas solubility rises with heat.
- Trap: Calling milk a true solution.
Quick revision
- Molarity vs molality.
- Colligative properties.
- Tyndall effect.
Practice MCQs
Molarity is moles of solute per —
- kilogram of solvent
- litre of solution
- gram of solute
- mole of solvent
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Answer: (b) litre of solution. mol/L.
Molality is moles of solute per —
- gram of solution
- litre of solvent
- litre of solution
- kilogram of solvent
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Answer: (d) kilogram of solvent. mol/kg.
2 moles of solute in 1 litre of solution gives —
- 4 M
- 1 M
- 2 M
- 0.5 M
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Answer: (c) 2 M. Molarity = 2.
Solubility of gases in water —
- decreases as temperature rises
- does not change
- becomes infinite
- increases with temperature
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Answer: (a) decreases as temperature rises. Warm water holds less gas.
Henry’s law relates gas solubility to —
- volume of container only
- time
- pressure
- colour
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Answer: (c) pressure. Higher pressure, more dissolved gas.
Colligative properties depend on —
- the nature of solute
- the number of solute particles
- the colour
- the container
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Answer: (b) the number of solute particles. Number, not nature.
A torch beam visible in fog shows —
- diffusion
- electrolysis
- Tyndall effect
- osmosis
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Answer: (c) Tyndall effect. Colloids scatter light.
Salt on icy roads works by —
- absorbing light
- raising the freezing point
- lowering the freezing point
- heating the road
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Answer: (c) lowering the freezing point. Freezing-point depression.
Which does NOT change with temperature?
- density
- molarity
- molality
- volume
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Answer: (c) molality. Molality uses mass.
More topics in this chapter
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