Solutions: Types, Solubility and Concentration
A glass of nimbu paani, a cup of tea, salt water, soft drinks, air, and even brass used in decorative items have one thing in common. They are all connected to solutions in chemistry.
Solutions are a basic but very important part of Chemistry notes for Classes 6 to 10. Once you understand solute, solvent, solubility and concentration, many daily examples become easy to explain. Why does sugar dissolve faster in hot tea? Why do bubbles come out of a cold drink when you open it? Why does oil not mix with water? This chapter answers all these questions in simple English.
What is a solution?
A solution is a homogeneous mixture of two or more substances.
Homogeneous means the composition is the same throughout. If you dissolve salt in water properly, every sip tastes salty. You cannot see separate salt particles because the salt spreads evenly in the water.
In a solution:
The substance that dissolves is called the solute.
The substance that dissolves the solute is called the solvent.
Example:
Salt + Water = Salt solution
Here, salt is the solute and water is the solvent.
A solution can be made from solids, liquids or gases. Many students think all solutions must be liquids, but that is not true. Air is a gaseous solution. Brass is a solid solution.
Solute and solvent with examples
The solute and solvent are the two main parts of a solution.
Usually, the solute is present in a smaller amount, and the solvent is present in a larger amount. In most school examples, water is the solvent because it dissolves many substances.
Solute | Solvent | Solution formed |
Salt | Water | Salt water |
Sugar | Water | Sugar solution |
Carbon dioxide gas | Water | Soft drink |
Oxygen and other gases | Nitrogen | Air |
Zinc | Copper | Brass |
Iodine | Alcohol | Tincture of iodine |
Solute vs solvent
Point of difference | Solute | Solvent |
Meaning | Substance that dissolves | Substance that dissolves the solute |
Amount | Usually smaller amount | Usually larger amount |
Physical state | Can be solid, liquid or gas | Can be solid, liquid or gas |
Example in salt water | Salt | Water |
Example in air | Oxygen, carbon dioxide and other gases | Nitrogen |
Exam tip: In most Class 6 to 10 questions, the substance written first is not always the solute. Read the example carefully and identify which substance dissolves in which.
Solution vs mixture
A solution is a type of mixture, but not every mixture is a solution.
A mixture is formed when two or more substances are combined physically. The substances do not chemically react to form a new substance.
A solution is a homogeneous mixture. This means its particles are evenly spread.
Feature | Solution | General mixture |
Nature | Always homogeneous | Can be homogeneous or heterogeneous |
Appearance | Uniform throughout | May or may not be uniform |
Particle visibility | Particles are not visible | Particles may be visible |
Example | Sugar solution | Sand and water |
Separation | Often needs evaporation or distillation | Sometimes can be separated by hand-picking, filtration or decantation |
Example:
Sugar in water forms a solution because sugar dissolves completely.
Sand in water forms a mixture, but not a solution, because sand does not dissolve.
Types of solutions
The types of solutions are based on the physical state of the solute and solvent. Solutions can be solid, liquid or gaseous.
Solid solutions
In a solid solution, the solvent is a solid.
Common examples:
Solute | Solvent | Solution |
Zinc | Copper | Brass |
Tin | Copper | Bronze |
Carbon | Iron | Steel |
Brass looks like one uniform solid, but it is made from copper and zinc. Since the substances are mixed evenly, brass is a solid solution.
Liquid solutions
Liquid solutions are very common in daily life. In these, the solvent is usually a liquid.
Examples:
Salt water
Sugar solution
Vinegar in water
Lemon juice mixed with water
Alcohol mixed with water
Most examples in school Chemistry use liquid solutions because they are easy to prepare and observe.
Gaseous solutions
In gaseous solutions, gases mix uniformly.
The best example is air.
Air mainly contains nitrogen and oxygen, along with small amounts of carbon dioxide, water vapour and other gases. Since the gases are evenly mixed, air is a gaseous solution.
Aqueous and non-aqueous solutions
A solution is called aqueous when water is the solvent.
Examples of aqueous solutions:
Salt dissolved in water
Sugar dissolved in water
Copper sulphate dissolved in water
Lemon juice in water
A solution is called non-aqueous when the solvent is not water.
Examples of non-aqueous solutions:
Iodine dissolved in alcohol
Sulphur dissolved in carbon disulphide
Nail polish dissolved in nail polish remover
Water is often called the universal solvent because it dissolves many substances. This does not mean it dissolves everything. Oil, sand and petrol do not dissolve in water.
Saturated, unsaturated and supersaturated solutions
A solution can hold only a limited amount of solute at a particular temperature.
This idea helps us understand saturated, unsaturated and supersaturated solutions.
Unsaturated solution
An unsaturated solution contains less solute than the maximum amount it can dissolve at a given temperature.
Example:
If you add one spoon of sugar to a glass of water and it dissolves completely, the solution is unsaturated. It can still dissolve more sugar.
Saturated solution
A saturated solution contains the maximum amount of solute that can dissolve at a given temperature.
Example:
If you keep adding sugar to water, a point comes when no more sugar dissolves. Extra sugar remains at the bottom. The solution above the undissolved sugar is saturated.
Supersaturated solution
A supersaturated solution contains more solute than it normally should at a given temperature.
It is usually prepared by dissolving more solute in hot water and then cooling the solution carefully without disturbing it.
Supersaturated solutions are unstable. If a small crystal is added, extra solute may separate quickly.
Comparison table
Feature | Unsaturated solution | Saturated solution | Supersaturated solution |
Amount of solute | Less than maximum | Maximum possible | More than normal maximum |
Can dissolve more solute? | Yes | No, at same temperature | No |
Stability | Stable | Stable | Unstable |
Example | One spoon sugar in water | Sugar solution with extra sugar at bottom | Carefully cooled sugar solution with extra dissolved sugar |
Common exam point | More solute can dissolve | No more solute dissolves | Extra solute may crystallise |
What is solubility?
Solubility is the maximum amount of solute that can dissolve in a fixed amount of solvent at a particular temperature.
A simple school-level definition is:
Solubility is the maximum amount of solute dissolved in 100 g of solvent at a given temperature.
Example:
If 36 g of salt dissolves in 100 g of water at a certain temperature, then the solubility of salt is 36 g per 100 g of water at that temperature.
This topic is often called solubility for students because it connects classroom Chemistry with daily life.
Why solubility matters
Solubility explains:
Why salt dissolves in water but sand does not
Why sugar dissolves faster in hot tea
Why soft drinks lose fizz when left open
Why some medicines dissolve in water and others do not
Why oil floats on water instead of mixing with it
Factors affecting solubility
Solubility depends mainly on three factors:
Temperature
Pressure
Nature of solute and solvent
Effect of temperature on solubility of solids
For most solid solutes, solubility increases when temperature increases.
That is why sugar dissolves better in hot tea than in cold water.
Example:
More sugar can dissolve in hot water than in cold water. When the hot sugar solution cools, some sugar may separate as crystals.
Some solids show only a small increase in solubility with temperature. A few may behave differently, but for Classes 6 to 10, remember that most solids become more soluble in hot water.
Effect of temperature on solubility of gases
Gases behave differently from most solids.
The solubility of gases in liquids usually decreases when temperature increases.
Example:
Cold soft drinks hold more dissolved carbon dioxide. When a soft drink becomes warm, carbon dioxide escapes faster, so it loses its fizz.
This is why soft drinks taste fizzier when cold.
Effect of pressure on solubility
Pressure has little effect on the solubility of solids and liquids.
Pressure has a big effect on gases.
When pressure increases, more gas dissolves in a liquid.
Example:
Carbon dioxide is dissolved in soft drinks under high pressure. When the bottle is opened, pressure decreases. The gas escapes as bubbles.
Nature of solute and solvent
Some substances dissolve in each other because their particles attract each other well.
A simple rule is:
Like dissolves like.
This means substances with similar nature tend to dissolve in each other.
Examples:
Salt dissolves in water.
Sugar dissolves in water.
Oil does not dissolve in water.
Grease dissolves better in petrol or kerosene than in water.
Miscible and immiscible liquids
Some liquids mix completely with each other. Some do not.
Miscible liquids
Liquids that mix completely are called miscible liquids.
Examples:
Water and alcohol
Water and vinegar
Water and lemon juice
Immiscible liquids
Liquids that do not mix are called immiscible liquids.
Examples:
Oil and water
Petrol and water
Kerosene and water
Oil and water form separate layers because they are immiscible. Oil usually floats because it is less dense than water.
Concentrated and dilute solutions
The terms concentrated and dilute tell us how much solute is present in a solution.
Dilute solution
A dilute solution contains a small amount of solute compared to the solvent.
Example:
A glass of water with a few drops of lemon juice is dilute.
Concentrated solution
A concentrated solution contains a large amount of solute compared to the solvent.
Example:
A glass of water with many spoons of sugar dissolved in it is concentrated.
Concentrated vs dilute
Feature | Dilute solution | Concentrated solution |
Solute amount | Small amount | Large amount |
Solvent amount | More compared to solute | Less compared to solute |
Taste example | Slightly sweet sugar water | Very sweet sugar syrup |
Colour example | Pale copper sulphate solution | Dark blue copper sulphate solution |
Meaning | Weak solution | Strong solution |
A concentrated solution is not always saturated. A solution may be concentrated but still able to dissolve more solute.
What is concentration?
Concentration tells us the amount of solute present in a given amount of solution or solvent.
The concentration of solution can be expressed in different ways. For Classes 6 to 10, the most common methods are:
Mass percentage
Volume percentage
Mass by volume percentage
Concentration formula for mass percentage
Mass percentage = Mass of solute / Mass of solution x 100
Mass of solution = Mass of solute + Mass of solvent
Example:
If 10 g salt is dissolved in 90 g water, mass of solution = 100 g.
Mass percentage = 10 / 100 x 100 = 10%
So, the solution is 10% by mass.
Concentration formula for volume percentage
Volume percentage = Volume of solute / Volume of solution x 100
Example:
If 20 mL alcohol is mixed with water to make 100 mL solution:
Volume percentage = 20 / 100 x 100 = 20%
So, alcohol is 20% by volume.
Mass by volume percentage
Mass by volume percentage = Mass of solute in g / Volume of solution in mL x 100
Example:
If 5 g glucose is dissolved in water to make 100 mL solution:
Mass by volume percentage = 5 / 100 x 100 = 5%
This is written as 5% mass by volume.
Solubility curves explained simply
A solubility curve is a graph that shows how the solubility of a substance changes with temperature.
Usually:
Temperature is shown on the horizontal axis.
Solubility is shown on the vertical axis.
Each line represents one solute.
If the curve goes upward, solubility increases with temperature.
If the curve goes downward, solubility decreases with temperature.
How to read a solubility curve
Suppose a graph shows that 40 g of a substance dissolves in 100 g water at 50°C.
This means:
At 50°C, the solubility of that substance is 40 g per 100 g water.
If only 25 g is dissolved, the solution is unsaturated.
If 40 g is dissolved, the solution is saturated.
If more than 40 g stays dissolved, the solution is supersaturated.
Suggested diagrams for your notebook
Draw these simple diagrams to improve your Chemistry notes:
Salt water solution
Show salt particles evenly spread in water.
Saturated solution
Show some dissolved sugar and some undissolved sugar at the bottom.
Solubility curve
Draw temperature on the X-axis and solubility on the Y-axis.
Miscible and immiscible liquids
Draw alcohol and water as one layer, and oil and water as two layers.
Soft drink bottle
Show carbon dioxide bubbles escaping when the cap is opened.
Everyday examples of solutions
Salt water
Salt water is an aqueous solution. Salt is the solute and water is the solvent.
Sugar solution
Sugar solution is another aqueous solution. Sugar dissolves evenly in water.
Soft drinks
Soft drinks contain carbon dioxide gas dissolved in water under pressure. When the bottle opens, pressure decreases and bubbles escape.
Air
Air is a gaseous solution. Nitrogen is the main solvent gas, while oxygen and other gases act as solutes.
Vinegar
Vinegar is a solution of acetic acid in water. It is used in cooking and pickles.
Metal alloys
Brass and bronze are solid solutions called alloys.
Did You Know facts
Water is called the universal solvent because it dissolves many substances, but it cannot dissolve everything.
Cold drinks are bottled under pressure so that more carbon dioxide stays dissolved.
Air is a solution, even though you cannot see its separate gases.
A saturated solution can become unsaturated if you heat it and the solubility of the solute increases.
Common mistakes and misconceptions
Mistake 1. All solutions are liquids
Not true. Solutions can be solid, liquid or gaseous.
Examples:
Solid solution: brass
Liquid solution: salt water
Gaseous solution: air
Mistake 2. A concentrated solution is always saturated
Not always. A concentrated solution has a large amount of solute, but it may still dissolve more solute.
Mistake 3. Solute is always a solid
Not true. Solute can be solid, liquid or gas.
Example:
In soft drinks, carbon dioxide gas is the solute.
Mistake 4. Water dissolves everything
Water dissolves many substances, but not oil, sand or petrol.
Mistake 5. Solubility does not depend on temperature
Solubility often changes with temperature. Most solids dissolve more in hot water, while gases dissolve better in cold water.
Exam tips
Always write the temperature when defining solubility.
For mass percentage, use mass of solution, not mass of solvent.
Remember that air is a gaseous solution.
Do not confuse a saturated solution with a concentrated solution.
In soft drinks, carbon dioxide is the solute and water is the solvent.
Use proper units such as g, mL, percentage and °C.
In numericals, write the formula before substitution.
Quick revision notes
A solution is a homogeneous mixture.
Solute dissolves in solvent.
Water-based solutions are aqueous solutions.
Non-water-based solutions are non-aqueous solutions.
Saturated solution cannot dissolve more solute at the same temperature.
Unsaturated solution can dissolve more solute.
Supersaturated solution is unstable.
Solubility is the maximum amount of solute dissolved in a fixed amount of solvent at a given temperature.
Most solids become more soluble in hot water.
Gases become less soluble in hot liquids.
Concentration tells the amount of solute in a solution.
Mass percentage = Mass of solute / Mass of solution x 100.
Volume percentage = Volume of solute / Volume of solution x 100.
20 solved questions and numericals
1. Define solution.
A solution is a homogeneous mixture of two or more substances.
2. Identify solute and solvent in salt water.
Salt is the solute. Water is the solvent.
3. Is air a solution?
Yes. Air is a gaseous solution mainly made of nitrogen, oxygen and other gases.
4. What type of solution is brass?
Brass is a solid solution. Zinc is dissolved in copper.
5. What is an aqueous solution?
A solution in which water is the solvent is called an aqueous solution.
6. Give one example of a non-aqueous solution.
Iodine dissolved in alcohol is a non-aqueous solution.
7. What is a saturated solution?
A saturated solution contains the maximum amount of solute that can dissolve at a given temperature.
8. What is an unsaturated solution?
An unsaturated solution contains less solute than the maximum amount it can dissolve at a given temperature.
9. What happens to gas solubility when temperature increases?
The solubility of gases in liquids usually decreases.
10. Why do bubbles come out when a soft drink bottle is opened?
The pressure inside the bottle decreases, so dissolved carbon dioxide escapes as bubbles.
11. Calculate mass percentage when 5 g salt is dissolved in 95 g water.
Mass of solution = 5 g + 95 g = 100 g
Mass percentage = 5 / 100 x 100 = 5%
Answer: 5% by mass
12. Calculate mass percentage when 20 g sugar is dissolved in 180 g water.
Mass of solution = 20 g + 180 g = 200 g
Mass percentage = 20 / 200 x 100 = 10%
Answer: 10% by mass
13. A solution has 15 g solute and 85 g solvent. Find mass percentage.
Mass of solution = 15 g + 85 g = 100 g
Mass percentage = 15 / 100 x 100 = 15%
Answer: 15% by mass
14. Find the volume percentage if 25 mL alcohol is present in 100 mL solution.
Volume percentage = 25 / 100 x 100 = 25%
Answer: 25% by volume
15. Find the volume percentage if 10 mL vinegar is present in 200 mL solution.
Volume percentage = 10 / 200 x 100 = 5%
Answer: 5% by volume
16. A glucose solution contains 4 g glucose in 100 mL solution. Find mass by volume percentage.
Mass by volume percentage = 4 / 100 x 100 = 4%
Answer: 4% mass by volume
17. A solution contains 12 g solute in 48 g solvent. Find mass percentage.
Mass of solution = 12 g + 48 g = 60 g
Mass percentage = 12 / 60 x 100 = 20%
Answer: 20% by mass
18. If 30 g solute is present in 150 g solution, find mass percentage.
Mass percentage = 30 / 150 x 100 = 20%
Answer: 20% by mass
19. If 40 mL solute is present in 200 mL solution, find volume percentage.
Volume percentage = 40 / 200 x 100 = 20%
Answer: 20% by volume
20. The solubility of a salt is 35 g per 100 g water at 25°C. What does this mean?
It means a maximum of 35 g of that salt can dissolve in 100 g water at 25°C to form a saturated solution.
10 FAQs
1. What is a solution in Chemistry?
A solution is a homogeneous mixture in which one or more solutes dissolve in a solvent.
2. What is the difference between solute and solvent?
The solute dissolves, and the solvent dissolves the solute. In salt water, salt is the solute and water is the solvent.
3. Is every mixture a solution?
No. A solution is always homogeneous. A mixture like sand and water is not a solution because sand does not dissolve.
4. Why is water called a universal solvent?
Water dissolves many substances, so it is called the universal solvent. It does not dissolve everything.
5. What is a saturated solution?
A saturated solution has dissolved the maximum possible amount of solute at a given temperature.
6. Can gases dissolve in liquids?
Yes. Carbon dioxide dissolves in water to make fizzy soft drinks.
7. Does heating always increase solubility?
Heating usually increases the solubility of solids in liquids, but it decreases the solubility of gases in liquids.
8. What is concentration?
Concentration tells how much solute is present in a given amount of solution.
9. Are oil and water miscible?
No. Oil and water are immiscible because they do not mix completely.
10. Is air a solution?
Yes. Air is a gaseous solution of nitrogen, oxygen, carbon dioxide and other gases.
25 practice questions
Define solution.
What are solute and solvent?
Identify the solute and solvent in sugar solution.
Give two examples of aqueous solutions.
Give one example of a non-aqueous solution.
Why is air called a gaseous solution?
What is a saturated solution?
What is an unsaturated solution?
What is a supersaturated solution?
10. Define solubility.
11. Name two factors affecting solubility.
12. How does temperature affect the solubility of most solids?
13. How does temperature affect the solubility of gases?
14. Why do cold drinks lose fizz when kept open?
15. What are miscible liquids?
16. What are immiscible liquids?
17. Give one example of a solid solution.
18. Is a concentrated solution always saturated?
19. Write the formula for mass percentage.
20. Write the formula for volume percentage.
21. Calculate mass percentage when 8 g salt is dissolved in 92 g water.
22. Calculate mass percentage when 25 g sugar is present in 125 g solution.
23. Calculate volume percentage when 30 mL alcohol is present in 150 mL solution.
24. A solution contains 6 g glucose in 100 mL solution. Find mass by volume percentage.
25. The solubility of a substance is 50 g per 100 g water at 40°C. What does this mean?
Answer key
A solution is a homogeneous mixture of two or more substances.
Solute dissolves, solvent dissolves the solute.
Sugar is solute, water is solvent.
Salt water and sugar solution.
Iodine in alcohol.
Air is a uniform mixture of gases.
It contains maximum dissolved solute at a given temperature.
It can dissolve more solute at the same temperature.
It contains more dissolved solute than normally possible and is unstable.
10. Maximum amount of solute dissolved in a fixed amount of solvent at a given temperature.
11. Temperature and pressure. Nature of solute and solvent is another factor.
12. Solubility usually increases.
13. Solubility usually decreases.
14. Carbon dioxide escapes from the drink.
15. Liquids that mix completely.
16. Liquids that do not mix completely.
17. Brass.
18. No.
19. Mass percentage = Mass of solute / Mass of solution x 100.
20. Volume percentage = Volume of solute / Volume of solution x 100.
21. Mass of solution = 8 g + 92 g = 100 g. Answer: 8%.
22. Mass percentage = 25 / 125 x 100 = 20%.
23. Volume percentage = 30 / 150 x 100 = 20%.
24. Mass by volume percentage = 6 / 100 x 100 = 6%.
25. A maximum of 50 g of the substance dissolves in 100 g water at 40°C.
Conclusion
Solutions are everywhere around us. Salt water, sugar solution, soft drinks, vinegar, air and brass all help us understand the same idea: a solute dissolves in a solvent to form a uniform mixture.
For Classes 6 to 10, focus on the main links. A solution is homogeneous. Solubility depends on temperature, pressure and the nature of substances. Most solids dissolve better in hot water, while gases dissolve better in cold liquids. Concentration tells how much solute is present, and simple formulas help us calculate it.
If these basics are clear, topics like acids, bases, salts, separation techniques and chemical reactions become much easier to learn. Keep practising examples and numericals, and this chapter will become one of the simplest parts of Chemistry.
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