Saturated Solution vs Unsaturated Solution — Difference (with Table & FAQs)
Saturated Solution vs Unsaturated Solution — a 6-row comparison table, 4 key points and 7 exam FAQs. Class 10-11 Chemistry.
TL;DR: Saturated Solution vs Unsaturated Solution — a 6-row comparison table, 4 key points and 7 exam FAQs. Class 10-11 Chemistry.
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
The main difference between Saturated Solution and Unsaturated Solution: A saturated solution is one in which the maximum amount of solute that can dissolve at a given temperature is dissolved. An unsaturated solution contains l
Saturated Solution vs Unsaturated Solution — Comparison Table
| Basis | Saturated Solution | Unsaturated Solution |
|---|---|---|
| Definition | Contains maximum dissolved solute at given temperature | Contains less solute than saturation point |
| Solute Addition | No more solute can dissolve; excess remains undissolved | More solute can dissolve when added |
| Equilibrium | In dynamic equilibrium with undissolved solute | Not in equilibrium with undissolved solute |
| Crystal Formation | Crystals form when cooled or evaporated | No crystal formation upon cooling |
| Concentration | Maximum concentration for given conditions | Lower concentration than saturated solution |
| Example | Water containing 36 g salt per 100 g water at 20 degrees C | Water containing 20 g salt per 100 g water at 20 degrees C |
Key Points
- Saturation depends on temperature and pressure of the system
- Increasing temperature increases saturation point for most solids
- A saturated solution appears clear but contains maximum solute
- Supersaturated solutions exist in unstable conditions
Saturated solution — the point where no more will dissolve
A saturated solution is one that has dissolved the maximum amount of solute it can hold at a particular temperature. Add any more and it simply settles at the bottom undissolved, however long you stir.
The phrase 'at a particular temperature' is not optional. A solution saturated at 20 °C is usually no longer saturated at 60 °C, because most solids dissolve more readily when hot. Leaving the temperature out of a definition is the single most common way students lose a mark here.
Unsaturated solution — there is still room
An unsaturated solution contains less solute than the maximum it could hold at that temperature. Add a little more and it dissolves.
There is also a third, less familiar state. If a hot saturated solution is cooled very slowly and left undisturbed, it can end up holding more solute than it should be able to. This is a supersaturated solution, and it is unstable — a single crystal or even a jolt will make the excess solute crystallise out at once.
Solubility, and how to state it properly
Solubility is the amount of a solute that saturates 100 grams of solvent at a given temperature. It is the number that tells you where the saturation point sits.
So saying 'the solubility of potassium nitrate is 32 g at 20 °C' means 100 g of water at 20 °C will dissolve 32 g of potassium nitrate and no more. Different solutes have very different solubilities in the same solvent, and the same solute has different solubilities in different solvents.
What temperature does — and the exception for gases
For most solids, solubility increases as temperature rises. Heating a saturated sugar solution lets more sugar dissolve, which is exactly how sugar syrup is made.
Gases behave the opposite way: their solubility decreases as temperature rises. This is why a warm fizzy drink goes flat faster than a cold one, and why fish struggle in warm water — it holds less dissolved oxygen. Examiners like this reversal because it catches students who have memorised only the solid case.
How to express concentration
Concentration means how much solute is present in a given quantity of solution. Two formulas are on the syllabus.
- Mass by mass percentage = (mass of solute ÷ mass of solution) × 100.
- Mass by volume percentage = (mass of solute ÷ volume of solution) × 100.
- Note that mass of solution = mass of solute + mass of solvent. Dividing by the mass of the solvent alone is a frequent slip.
- A dilute solution has a small amount of solute; a concentrated solution has a large amount. These are relative terms, unlike saturated and unsaturated which have exact meanings.
Saturated Solution vs Unsaturated Solution — Worked Examples
- Sugar settling at the bottom of a cold glass of tea — The solution is saturated at that temperature — no more sugar can dissolve until it is heated.
- Two spoons of salt dissolving completely in a litre of water — Unsaturated. The solution can still take more salt.
- A hot saturated salt solution cooling and forming crystals — Solubility falls as the solution cools, so the excess solute can no longer stay dissolved and crystallises out.
- A warm cold drink going flat quickly — Gas solubility decreases with temperature, so dissolved carbon dioxide escapes faster.
Common Mistakes Students Make
- Defining a saturated solution without mentioning temperature. The definition is meaningless without it.
- Treating 'saturated' and 'concentrated' as the same thing. Concentrated just means a lot of solute; saturated means the exact maximum has been reached.
- Assuming solubility always rises with temperature. It does for most solids, but falls for gases.
- Calculating mass percentage using the mass of the solvent instead of the mass of the whole solution.
- Forgetting that a supersaturated solution exists and is unstable.
Diagrams
Where This Shows Up in Real Life
How sugar crystals and rock candy form
Dissolve as much sugar as possible in hot water and you have a solution saturated at that high temperature. As it cools, solubility falls, so the solution can no longer hold all the dissolved sugar and the excess comes out as crystals on a string or the side of the jar. The slower the cooling, the larger and better-formed the crystals. The same principle produces salt from evaporating seawater in the salt pans of Gujarat and Tamil Nadu.
Why fish struggle in warm water
Gases behave opposite to solids: their solubility falls as temperature rises. Warm river or pond water therefore holds less dissolved oxygen than cold water, which is why fish kills happen in summer and why thermal pollution from industrial cooling water is an ecological problem. The same reversal explains why a cold soft drink stays fizzy far longer than a warm one.
Purification by recrystallisation
A chemist purifies an impure solid by dissolving it in a minimum of hot solvent to make a saturated solution, filtering off insoluble impurities, then cooling slowly. The desired compound crystallises out while the soluble impurities, present in much smaller amounts, stay dissolved because the solution is still unsaturated with respect to them. This is a standard laboratory technique and rests entirely on how saturation changes with temperature.
Reading a solubility curve
A solubility curve plots grams of solute per 100 g of water against temperature. Any point ON the curve is a saturated solution, any point BELOW it is unsaturated, and the rare point above it is supersaturated. Being able to read off how much solute crystallises when a solution is cooled from one temperature to another is a standard numerical, and it is simply the difference between the two solubility values.
Solved Numericals — Step by Step
Problem 1. The solubility of potassium nitrate is 32 g per 100 g of water at 20 °C. A solution contains 20 g of potassium nitrate in 100 g of water at 20 °C. Is it saturated, and how much more will dissolve?
- Solubility at 20 °C = 32 g per 100 g water — this is the maximum.
- The solution currently holds 20 g, which is less than 32 g.
- Therefore it is UNSATURATED.
- Extra that can still dissolve = 32 − 20 = 12 g.
Answer: Unsaturated; a further 12 g of potassium nitrate will dissolve at 20 °C.
Problem 2. A saturated solution of a salt at 60 °C contains 60 g of salt in 100 g of water. On cooling to 20 °C the solubility falls to 35 g per 100 g of water. How much salt crystallises out?
- At 60 °C the solution holds 60 g in 100 g of water.
- At 20 °C only 35 g can remain dissolved in that same 100 g.
- Excess = 60 − 35 = 25 g.
Answer: 25 g of salt crystallises out. This is exactly how recrystallisation purifies a solid.
Problem 3. Calculate the mass by mass percentage of a solution made by dissolving 25 g of sugar in 175 g of water.
- Mass of solution = mass of solute + mass of solvent = 25 + 175 = 200 g.
- Mass by mass % = (mass of solute ÷ mass of SOLUTION) × 100.
- = (25 ÷ 200) × 100
- = 12.5%.
Answer: 12.5%. Dividing by 175 (the solvent) instead of 200 (the solution) is the classic error and gives 14.3%.
Board-Style Questions with Model Answers
Define saturated and unsaturated solutions. How would you convert one into the other? (3 marks)
A saturated solution is one that contains the maximum amount of solute that can dissolve in a given quantity of solvent at a particular temperature; adding more solute leaves it undissolved. An unsaturated solution contains less solute than that maximum, so more will still dissolve. A saturated solution can be made unsaturated by raising the temperature, since the solubility of most solids increases with temperature, or by adding more solvent. An unsaturated solution can be made saturated by adding more solute until no more dissolves, by cooling it, or by evaporating some of the solvent. The temperature must always be stated, because saturation has no meaning without it.
What is solubility? How does temperature affect the solubility of solids and gases? (3 marks)
Solubility is the maximum mass of a solute that can dissolve in 100 grams of solvent at a stated temperature to give a saturated solution. For most solids, solubility increases as temperature rises, because the added energy helps break the solute lattice and disperse the particles; this is why more sugar dissolves in hot water than in cold. For gases the trend is reversed: solubility decreases as temperature rises, because the added energy helps dissolved gas molecules escape from the liquid. This is why a warm fizzy drink goes flat quickly and why warm water holds less dissolved oxygen for aquatic life.
Explain, with the method, how you would obtain pure copper sulphate crystals from an impure sample. (5 marks)
The method is crystallisation. Take the impure copper sulphate in a china dish and add just enough water to dissolve it, warming gently and stirring until a saturated solution forms. Add a few drops of dilute sulphuric acid to prevent hydrolysis. Filter the hot solution to remove insoluble impurities, collecting the filtrate in a clean dish. Allow the filtrate to cool slowly and undisturbed. As it cools the solubility falls, the solution can no longer hold all the dissolved copper sulphate, and pure blue crystals separate out while the soluble impurities remain in the mother liquor, which is still unsaturated with respect to them. Finally, filter off the crystals and dry them between filter papers. Slow cooling is important because it produces larger, purer crystals.
A student adds sugar to a glass of cold water until no more dissolves, then heats the glass and finds the remaining sugar dissolves. Explain. (3 marks)
When no more sugar would dissolve, the solution had become saturated at that low temperature — it was holding the maximum mass of sugar that 100 grams of water can dissolve at that temperature. On heating, the solubility of sugar increases, because the extra thermal energy helps separate the sugar particles from one another and disperse them among the water molecules. The maximum has therefore risen, and the same solution is now unsaturated with respect to the new temperature, so the undissolved sugar goes into solution. If the glass is cooled again, the excess sugar will crystallise back out.
Calculate the mass by mass percentage of a solution containing 40 g of common salt in 320 g of water. (2 marks)
The mass of the solution is the mass of solute plus the mass of solvent, that is 40 + 320 = 360 g. Mass by mass percentage is the mass of solute divided by the mass of the solution, multiplied by 100. So it is (40 ÷ 360) × 100 = 11.1% approximately. Note that the denominator must be the mass of the whole solution and not the mass of the water alone.
Assertion–Reason Questions (CBSE Format)
For each question choose: (a) both A and R are true and R is the correct explanation of A; (b) both are true but R is not the correct explanation; (c) A is true but R is false; (d) A is false but R is true.
1. Assertion (A): A saturated solution can dissolve more solute when heated.
Reason (R): The solubility of most solids increases with temperature.
Answer: (a) — Both are true and the reason explains the assertion. Raising the temperature raises the maximum, so the solution is no longer saturated at the new temperature.
2. Assertion (A): A saturated solution is always a concentrated solution.
Reason (R): A saturated solution holds the maximum possible amount of solute.
Answer: (d) — The assertion is false: for a sparingly soluble substance the maximum is a very small amount, so the solution is saturated yet dilute. The reason is true but does not rescue the false assertion.
3. Assertion (A): Warm water holds less dissolved oxygen than cold water.
Reason (R): The solubility of gases decreases as temperature increases.
Answer: (a) — Both are true and correctly linked. Gases behave opposite to most solids, which is why aquatic life suffers in warm or thermally polluted water.
4. Assertion (A): Crystallisation can be used to purify an impure solid.
Reason (R): On cooling a hot saturated solution, the dissolved solid separates as crystals while soluble impurities stay in solution.
Answer: (a) — Both are true and the reason is the mechanism behind the assertion. Falling solubility forces the major component out first.
Quick Self-Check
Q1. A solution that can dissolve no more solute at a given temperature is:
- A. Dilute
- B. Unsaturated
- C. Saturated
- D. Colloidal
Answer: C. Saturated — Saturated means the maximum amount of solute for that temperature has already dissolved.
Q2. The solubility of most solids in water when temperature increases:
- A. Increases
- B. Decreases
- C. Stays the same
- D. Becomes zero
Answer: A. Increases — Most solids dissolve more readily in hot solvent. Gases are the exception — their solubility falls as temperature rises.
Q3. If 20 g of salt is dissolved in 80 g of water, the mass by mass percentage is:
- A. 25%
- B. 20%
- C. 80%
- D. 16%
Answer: B. 20% — Mass of solution = 20 + 80 = 100 g. So (20 ÷ 100) × 100 = 20%. Dividing by 80 instead of 100 gives the wrong 25%.
Q4. A warm fizzy drink goes flat faster because:
- A. Sugar dissolves faster
- B. Gas solubility decreases with temperature
- C. The solution becomes saturated
- D. Water evaporates
Answer: B. Gas solubility decreases with temperature — Unlike solids, gases become less soluble as temperature rises, so dissolved carbon dioxide escapes more quickly.
Key Terms Glossary
- Solution
- A homogeneous mixture of two or more substances, with particles smaller than 1 nm.
- Solute
- The substance that dissolves, usually present in the smaller amount.
- Solvent
- The substance in which the solute dissolves, usually present in the larger amount.
- Saturated solution
- A solution holding the maximum solute that will dissolve at a stated temperature.
- Unsaturated solution
- A solution holding less than the maximum, so more solute will still dissolve.
- Supersaturated solution
- An unstable solution holding MORE than the maximum, made by cooling a hot saturated solution slowly.
- Solubility
- The maximum mass of solute that dissolves in 100 g of solvent at a stated temperature.
- Concentration
- How much solute a solution actually contains, expressed as a mass or volume percentage.
- Mass by mass %
- (mass of solute ÷ mass of SOLUTION) × 100. The denominator is the whole solution, not the solvent.
- Dilute solution
- A solution containing a relatively small amount of solute. A relative term, unlike "saturated".
- Crystallisation
- Purifying a solid by cooling its hot saturated solution so pure crystals separate out.
- Mother liquor
- The liquid remaining after crystals have separated, still holding the soluble impurities.
One-Minute Revision
- SATURATED = maximum solute dissolved AT A STATED TEMPERATURE. Never omit the temperature.
- UNSATURATED = below the maximum, so more will still dissolve.
- SUPERSATURATED = above the maximum, unstable; a seed crystal makes the excess crystallise instantly.
- Solubility = grams of solute per 100 g of SOLVENT at a stated temperature.
- SOLIDS: solubility RISES with temperature. GASES: solubility FALLS. The gas case is the exam trap.
- Saturated ≠ concentrated. A sparingly soluble salt gives a saturated but DILUTE solution.
- Mass by mass % divides by the mass of the SOLUTION (solute + solvent), not the solvent alone.
- Crystallisation purifies by cooling a hot saturated solution — solubility falls, pure crystals drop out.
Syllabus reference: NCERT Class 9 Science, Chapter 2 — Is Matter Around Us Pure?
Frequently Asked Questions
What is the main difference between a saturated and an unsaturated solution?
A saturated solution holds the maximum amount of solute that can dissolve at a given temperature — no more will dissolve. An unsaturated solution holds less than that maximum, so it can still dissolve more solute.
How can you tell if a solution is saturated?
Add a little more solute and stir. If it dissolves, the solution is unsaturated; if the extra solute settles undissolved at the bottom, the solution is saturated.
Does temperature affect whether a solution is saturated?
Yes. For most solids, solubility rises with temperature, so a solution that is saturated at a low temperature can become unsaturated when heated — allowing more solute to dissolve.
What is a supersaturated solution?
It is a solution holding more dissolved solute than its saturation point allows at that temperature. It is made by cooling a hot saturated solution slowly without disturbing it, and it is unstable — adding a seed crystal or shaking it makes the excess solute crystallise out immediately.
Is a saturated solution always concentrated?
No. Saturated means the maximum possible amount has dissolved for that solute and temperature, which for a poorly soluble substance may be a very small amount. A saturated solution of a barely soluble salt is saturated but still dilute.
How do you turn a saturated solution into an unsaturated one?
Heat it, if the solute is a solid — higher temperature raises solubility, so the same amount of dissolved solute is no longer the maximum. Alternatively, add more solvent.
What is the difference between solubility and concentration?
Solubility is a fixed property: the maximum mass of solute that dissolves in 100 g of solvent at a stated temperature. Concentration is how much solute a particular solution actually contains, which can be anything from nearly zero up to the solubility limit.