What Are Solutions and Solubility?
A solution is a homogeneous mixture of a solute (dissolved substance) and a solvent (liquid, usually water). Solubility is the maximum amount of solute that can dissolve in a solvent at a given temperature.
A solution is a uniform mixture of solute and solvent. Solubility is the limit of dissolving — measured in g per 100 mL of solvent; once reached, excess solute falls out (precipitate).
- •Solute < solubility limit
- •More dissolves easily
- •Clear solution
- •Solute = solubility limit
- •No more dissolves
- •Precipitate settles
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Step-by-step worked examples
25 g of NaCl dissolves in 100 mL of water at 20°C. The solubility of NaCl at 20°C is 36 g per 100 mL. Is the solution saturated?
Solubility limit: 36 g per 100 mL. Actual solute: 25 g < 36 g. The solution is UNSATURATED.
A solution contains 40 g of sugar in 200 mL of water. The solubility of sugar is 200 g per 100 mL. What percent is dissolved?
Mass percent = (40 / (40 + 200)) × 100 = (40/240) × 100 = 16.7%. About 16.7% sugar by mass.
At 100°C, 39 g of KNO₃ per 100 mL water. At 20°C, only 13 g per 100 mL. A saturated solution at 100°C is cooled to 20°C. What happens?
At 100°C: 39 g dissolved = saturated. At 20°C: solubility drops to 13 g. The extra 26 g precipitates out.
Flashcards
Quick quiz
Q1.What is a solvent?
Q2.A saturated solution contains…
Q3.If solubility is 40 g/100 mL and 30 g dissolves, the solution is…
Q4.Cooling a saturated solution typically causes…
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Common mistakes
Confusing solute and solvent. — Correct: Solute = what dissolves; solvent = what it dissolves in.
Saturation means no solute present. — Correct: Saturation = maximum solute dissolved.
All solids have higher solubility at higher temperatures. — Correct: Most do, but some (like Ca(OH)₂) have inverse solubility.
A precipitate means the solution failed. — Correct: Precipitation is the normal result of exceeding solubility.
FAQ
What is the difference between a solution and a suspension?
A solution is homogeneous (particles invisible); a suspension is heterogeneous (large particles visible/settling).
How does temperature affect solubility?
For most solid solutes, higher temperature increases solubility. For gases, higher temperature decreases solubility.
Can a solution become supersaturated?
Yes, temporarily — if cooled slowly without disturbance, solute may remain dissolved beyond the saturation point.
What is concentration?
The ratio of solute to solvent, expressed as molarity, molality, or percent composition.