As we understand it in chemistry, the concept of solutions involves a homogeneous mixture of two or more substances. The study and use of solutions date back to ancient times, but the formal introduction and systematic study of solutions can be attributed to the development of modern chemistry. Ancient civilizations understood the concept of solutions in a rudimentary form. For instance, early chemists and alchemists in ancient Egypt, China, and India used solutions in their practices, such as dissolving metals in acids. The formal scientific study of solutions began to take shape with the work of early chemists. Robert Boyle (1627-1691) made significant contributions by studying the solubility of gases and liquids. In the late 18th century, chemists like Henry Cavendish and Joseph Priestley expanded the understanding of gases in solutions, particularly with their work on carbon dioxide in water. The concept of solutions was further refined with the development of physical chemistry. Svante Arrhenius (1859-1927) introduced the idea of electrolytic dissociation in 1887, which described how electrolytes break into ions in a solution, fundamentally changing the understanding of how solutions work at the molecular level. The study of solutions continued to evolve with the development of more sophisticated theories and models, including the concept of colligative properties, which depend on the number of particles in a solution, and advances in spectroscopy and analytical techniques to understand solution behavior better.
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Solutions are important in various practical applications and lots of scientific studies in such a way that Solutions are crucial in multiple fields such as medicine (e.g., intravenous fluids), chemistry (e.g., reaction media), and industry (e.g., metal plating). Understanding solutions is fundamental to chemistry and physics as it affects how substances interact and react, influencing everything from biological processes to industrial operations.
The solution is a homogeneous mixture of two or more chemically non-reacting substances whose composition can be varied within certain limits. A solution that contains only two components is called a binary solution. The component which has the same physical state as the solution is the solvent. If both the components have the same physical state, then the component present in a larger amount is called the solvent and the other present in a smaller amount is called the solute.
The solutions may be gaseous, liquids, and solids. The most common type of solution is the liquid solution (gas in liquid, liquid in liquid, solid in liquid). In all, we can divide solutions into nine different classes as follows:
The concentration of a solution gives us an idea about the relative amount of solute and solvent present in the solution. The concentration can be expressed either qualitatively or quantitatively. For example, qualitatively we can say that the solution is dilute (i.e., a relatively very small quantity of solute) or it is concentrated (i.e., a relatively very large quantity of solute). But in reality, the qualitative description can confuse, and hence there is a need for a quantitative description of the solution.
There are several ways by which we can describe the concentration of the solution quantitatively.
(1) Mass percentage (w/w):
It is the mass of any component present in 100 g of solution.
Mathematically, it can be defined as:
Mass $\%$ of a component $=\frac{\text { Mass of the component in the solution }}{\text { Total mass of the solution }} \times 100$
For example, a solution described as 20% by mass of glucose in water, it means that 20 g of glucose is dissolved in 80 g of water resulting in a 100 g solution.
The mass % can also be expressed in terms of the mass fraction by simply removing the 100 from the above-given formula
Concentration described by mass percentage is commonly used in industrial chemical applications.
(2) Volume percentage (V/V):
It is the volume of any solute present in 100 ml of the solution. Mathematically it is defined as:
Volume $\%$ of a component $=\frac{\text { Volume of the component }}{\text { Total volume of solution }} \times 100$
For example, a 20% Methanol solution in water means that 20 mL of Methanol is dissolved in water such that the total volume of the solution is 100 mL. Solutions containing liquids are commonly expressed in this unit.
(3) Mass by volume percentage (w/V):
It is the mass of solute dissolved in 100 mL of the solution. Mathematically, it is defined as:
Mass by Volume $\%$ of a component $=\frac{\text { Mass of the component }}{\text { Total volume of solution }} \times 100$
For example, a 20% weight-by-volume solution of Glucose in water means that 20 g of Glucose was dissolved in water to obtain a 100ml solution.
This concentration term is commonly used in medicine and pharmacy.
(4) Parts per million (ppm):
When a solute is present in trace quantities, it is convenient to express concentration in parts per million (ppm) and is defined as: Parts per million $=\frac{\text { Number of parts of the component }}{\text { Total number of parts of all components of the solution }} \times 10^6$
As in the case of percentage, concentration in parts per million can also be expressed as mass to mass, volume to volume, and mass to volume.
This is generally used in expressing the hardness of water and in expressing the concentration of dissolved oxygen in water etc.
For example, if the hardness of a hard water sample is 100pm in CaCO3, it means that 100 g of CaCO3 is present in 106 g of the water sample.
(5) Mole fraction:
It is the ratio of the moles of any component present in the solution to the total moles present in the solution. A commonly used symbol for mole fraction is X and the subscript used on the right-hand side of X denotes the component.
It is defined as: Mole fraction of a component $=\frac{\text { Number of moles of the component }}{\text { Total number of moles of all the components }}$
For example, in a binary mixture, if the number of moles of A and B is nA and nB respectively, the mole fraction of A will be:
$\mathrm{x}_{\mathrm{i}}=\frac{\mathrm{n}_1}{\mathrm{n}_1+\mathrm{n}_2+\ldots \ldots+\mathrm{n}_{\mathrm{i}}}=\frac{\mathrm{n}_{\mathrm{i}}}{\sum \mathrm{n}_{\mathrm{i}}}$
It can be shown that in a given solution sum of all the mole fractions is unity, i.e.
$x_1+x_2+\ldots \ldots \ldots \ldots \ldots+x_i=1$
Mole fraction unit is very useful in relating some physical properties of solutions, say vapor pressure with the concentration of the solution, and quite useful in describing the calculations involving gas mixtures.
(6) Molality(m):
It is defined as the number of moles of the solute present per kilogram (kg) of the solvent and is expressed as:
$\operatorname{Molality}(\mathrm{m})=\frac{\text { Moles of solute }}{\text { Mass of solvent in } \mathrm{kg}}$
For example, 1 molal solution of NaOH means that 1 mol (40 g) of NaOH is dissolved in 1 kg of water.
(7) Molarity (M):
It is defined as the number of moles of solute dissolved in one liter of solution
Molarity $=\frac{\text { Moles of solute }}{\text { Volume of solution in litre }}$
For example, 0.5 mol L-1 (or 0.5 M) solution of NaOH means that there is 0.5 mol of NaOH dissolved in water to obtain one liter of solution.
Each method of expressing the concentration of the solutions has its own merits and demerits. Mass %, ppm, mole fraction, and molality are independent of temperature, whereas molarity is a function of temperature. This is because volume depends on temperature and mass does not.
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Some Solved Examples
Example.1
1. Which of the following is the correct combination of the dispersed phase and dispersion medium, among the colloids cheese (C), milk (M) and smoke (S)?
1) (correct)C: liquid in solid; M: liquid in liquid; S : solid in gas
2)C: liquid in solid; M: liquid in solid; S: solid in gas
3)C: solid in liquid; M: solid in liquid; S: solid in gas
4)None of the above
Solution
Solutions - A homogeneous mixture of solute and solvent is present in the same phase.
Eg. NaCl in H2O
Nature of liquid and vapor pressure -
More volatile liquids exert more vapour pressure.
More volatile liquids are those when intermolecular forces are weak.
Cheeseliquid in solid
Milk liquid in the liquid
Smoke Solid in gas
Hence, the answer is the option (1).
Example.2
2. Among the colloids cheese (C), milk (M) and smoke (S), the correct combination of the dispersed phase and dispersion medium, respectively is :
1)C: liquid in solid; M: liquid in solid; S: solid in gas
2) (correct)C: liquid in solid; M: liquid in liquid; S: solid in gas
3)C: solid in liquid; M: Liquid in Liquid; S: gas in solid
4)C: solid in liquid; M: solid in liquid; S: solid in gas
Solution
Cheeseliquid in solid
Milk liquid in the liquid
Smoke Solid in gas
Hence, the answer is the option (2).
Example.3
3. Which statement best explains the meaning of the phrase “like dissolves like“?
1)A Solute will easily dissolve a solute of similar mass
2) (correct)A solvent and solute with similar intermolecular forces will readily form a solution
3)The only true solutions are formed when water dissolves a non-polar solute
4)The only true solutions are formed when water dissolves a polar solute
Solution
To form a solution, the nature of intermolecular forces in solute and solvent should be the same. Polar solutes dissolve in polar solvents and non-polar solutes dissolve in non-polar solvents.
Hence, the answer is an option (2).
Example.4
4. Select the correct statement out of the following regarding a binary solution
1) The component which is present in excess is solute
2) (correct)The component which is present in excess is the solvent
3)In a solution, the physical state of the solute is retained.
4)In a solution, the physical state of the solvent is not retained.
Solution
Answer : (2) In a solution , the species which is present in the same state as the solution is the solvent . In case both species are in the same physical state , then the species present in excess is the solvent .
Example.5
5. In Brine, which is a solution containing NaCl and water, and in hydrated Copper Sulphate respectively, the solvents are
1)Water and Water
2)NaCl and $\mathrm{CuSO}_4$
3) (correct)Water and $\mathrm{CuSO}_4$
4)NaCl and Water
Solution
Answer : (3) In Brine, water is present in excess while in $\mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O}$ , the physical state of the solution is Solid, hence the solvent is CuSO
Solutions are integral to numerous fields and applications, from daily life and industrial processes to scientific research and environmental management. Their ability to provide uniform mixtures and facilitate various reactions makes them essential for both practical uses and academic study. Solutions are of various types which include various types of substances such as solid sol, which includes Alloys eg bronze, and steel, liquid sol includes salt water and sugar dissolved in water and the other one is gaseous solution which includes air a mixture of gaseous like oxygen, nitrogen and carbon dioxide. Solutions have so many applications such as Medicine: Solutions are used in intravenous fluids and medications. For example, saline solutions help in hydration and electrolyte balance.Industry: Solutions are essential in processes like metal plating, dyeing fabrics, and chemical synthesis. They help in creating uniform mixtures and reactions. Household: Solutions such as cleaning agents, detergents, and cooking ingredients are common daily. Solutions are also used in scientific research in such a way that in Analytical Chemistry: Solutions are used to determine concentrations of substances, study reactions, and measure physical properties. Biological Processes: Solutions are crucial for understanding biochemical reactions, cell functions, and enzyme activities. The solution has also benefits in water treatment such as Solutions are used to purify and treat water, making it safe for drinking and other uses. In agriculture: Nutrient solutions are used in hydroponics to grow plants without soil. Solutions are fundamental in learning about chemical reactions, equilibria, and physical properties, providing a basis for more advanced studies in science and engineering.
No, a solution is a homogeneous liquid mixture made up of two components named solute and solvent. Solute is uniformly distributed in solvent.
Aqueous solution definition - an aqueous solution is made up of water (solvent) and a solute. Aqueous solution is a homogeneous solution in which a solute is uniformly dissolved in water. Aqueous solution examples include a solution of sugar and water, a solution of salt and sugar, oxygen dissolved in water, cola, salt solutions etc.
Homogeneous solution definition - a solution is said to be a homogeneous solution when the solute particles are uniformly distributed throughout the solvent. Homogeneous solutions cannot be separated by a physical separation process like filtration.
Homogeneous solution examples include a solution of salt and water, a cup of tea, cold drinks, etc.
On the basis of physical state of solute and solvent, we can classify 9 types of solutions –
Type of Solution | Solute | Solvent | Examples |
Gaseous solutions | Gas | Gas | Air |
Liquid | Gas | Water in atmosphere | |
Solid | Gas | Sublimation of camphor in air | |
Liquid solutions | Gas | Liquid | Carbonated beverages |
Liquid | Liquid | A solution of Milk and water | |
Solid | Liquid | Sugar in water | |
Solid solutions | Gas | Solid | Hydrogen adsorbed on platinum |
Liquid | Solid | Amalgam of Hg with Na | |
Solid | Solid | Alloys |
Types of solution on the basis of type of solvent used-
1. Aqueous solution – an aqueous solution is made up of water (solvent) and a solute. Aqueous solution is a homogeneous solution in which a solute is uniformly dissolved in water. Aqueous solution examples include a solution of sugar and water, a solution of salt and sugar, oxygen dissolved in water, cola, salt solutions etc.
2. Non-aqueous solution - a solution in which a solvent other than water is used is called a non-aqueous solution. Non aqueous solution examples include petrol, phenolphthalein in benzene, liquid ammonia, sulfur in carbon disulfide etc.
Heterogeneous solution – a solution is said to be heterogeneous when the solute particles are non-uniformly distributed throughout the solvent. The solute may settle down or coagulate at one place. Heterogeneous solution can be separated by a physical separation process like filtration. Heterogeneous solution examples include a mixture of water and chalk powder, sand and water, oil and water, oil and vinegar, etc.
Three types of solutions can be classified on the basis of concentration of solute –
Saturated solution – at a definite temperature, when the value of the amount of substance that can be dissolved in a solvent reaches its maximum value (called saturation point) such that no more solute can be dissolved, such solutions are said to be saturated solutions. Cold drinks, carbonated water and soda are examples of saturated solutions of carbon dioxide and water.
Unsaturated solution – an unsaturated solution is a solution in which a solvent can dissolve more solute, that is, the solution hasn’t reached its saturation point. Examples include lemon juice in lemonade.
Supersaturated solution – when the saturation point is increased by increasing temperature, to dissolve more solute by force, such solutions are called supersaturated solutions. For example, a supersaturated solution is sodium acetate.
Steps to mix chemical solutions-
Add solute in container.
Add solvent in solution.
Mix the solution until the solute dissolves.
Pure water is not a solution, it is a compound made up of hydrogen and oxygen but pure water is rarely found in nature. Water which has other substances dissolved in it or impurities is a solution.
Amalgam of mercury with sodium is an example of liquid in solid type solution.
No, a solution is a homogeneous liquid mixture made up of two components named solute and solvent. Solute is uniformly distributed in solvent.
Aqueous solution definition - an aqueous solution is made up of water (solvent) and a solute. Aqueous solution is a homogeneous solution in which a solute is uniformly dissolved in water. Aqueous solution examples include a solution of sugar and water, a solution of salt and sugar, oxygen dissolved in water, cola, salt solutions etc.
Homogeneous solution definition - a solution is said to be a homogeneous solution when the solute particles are uniformly distributed throughout the solvent. Homogeneous solutions cannot be separated by a physical separation process like filtration.
Homogeneous solution examples include a solution of salt and water, a cup of tea, cold drinks, etc.
On the basis of physical state of solute and solvent, we can classify 9 types of solutions –
Type of Solution | Solute | Solvent | Examples |
Gaseous solutions | Gas | Gas | Air |
Liquid | Gas | Water in atmosphere | |
Solid | Gas | Sublimation of camphor in air | |
Liquid solutions | Gas | Liquid | Carbonated beverages |
Liquid | Liquid | A solution of Milk and water | |
Solid | Liquid | Sugar in water | |
Solid solutions | Gas | Solid | Hydrogen adsorbed on platinum |
Liquid | Solid | Amalgam of Hg with Na | |
Solid | Solid | Alloys |
Types of solution on the basis of type of solvent used-
1. Aqueous solution – an aqueous solution is made up of water (solvent) and a solute. Aqueous solution is a homogeneous solution in which a solute is uniformly dissolved in water. Aqueous solution examples include a solution of sugar and water, a solution of salt and sugar, oxygen dissolved in water, cola, salt solutions etc.
2. Non-aqueous solution - a solution in which a solvent other than water is used is called a non-aqueous solution. Non aqueous solution examples include petrol, phenolphthalein in benzene, liquid ammonia, sulfur in carbon disulfide etc.
Heterogeneous solution – a solution is said to be heterogeneous when the solute particles are non-uniformly distributed throughout the solvent. The solute may settle down or coagulate at one place. Heterogeneous solution can be separated by a physical separation process like filtration. Heterogeneous solution examples include a mixture of water and chalk powder, sand and water, oil and water, oil and vinegar, etc.
Three types of solutions can be classified on the basis of concentration of solute –
Saturated solution – at a definite temperature, when the value of the amount of substance that can be dissolved in a solvent reaches its maximum value (called saturation point) such that no more solute can be dissolved, such solutions are said to be saturated solutions. Cold drinks, carbonated water and soda are examples of saturated solutions of carbon dioxide and water.
Unsaturated solution – an unsaturated solution is a solution in which a solvent can dissolve more solute, that is, the solution hasn’t reached its saturation point. Examples include lemon juice in lemonade.
Supersaturated solution – when the saturation point is increased by increasing temperature, to dissolve more solute by force, such solutions are called supersaturated solutions. For example, a supersaturated solution is sodium acetate.
Steps to mix chemical solutions-
Add solute in container.
Add solvent in solution.
Mix the solution until the solute dissolves.
Pure water is not a solution, it is a compound made up of hydrogen and oxygen but pure water is rarely found in nature. Water which has other substances dissolved in it or impurities is a solution.
Amalgam of mercury with sodium is an example of liquid in solid type solution.
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