What is Solution in Chemistry | Types, Examples

Definiton of Solution

solution in chemistry
  • The solution, in chemistry, is a homogenous mixture of two or more substances in relative amounts that can be varied continuously up to what is called the limit of solubility.
  • The term solution is commonly applied to the liquid state of matter, but solutions of gases and solids are possible. For example, Air is a solution consisting chiefly of oxygen and nitrogen with trace amounts of several other gases. And brass is a solution composed of copper and zinc.
  • A solution is a homogeneous mixture of two or more components in which the particle size is smaller than 1 nm.

Examples of Solution

  • Common examples of solutions are sugar in water and salt in water solutions, soda water, etc. In a solution, all the components appear as a single phase. There is particle homogeneity, i.e., particles are evenly distributed. This is why a whole bottle of soft drink has the same taste throughout.
  • Air is a homogeneous mixture of gases. Here both the solvent and the solute are gases.
  • Sugar syrup is a solution where sugar is dissolved in water using heat. Here, water is the solvent and sugar is the solute.
  • Tincture of iodine, a mixture of iodine in alcohol. Iodine is the solute whereas alcohol is the solvent.

Components of Solution

The substances that make up a homogeneous solutions are called components of the solution. It has basically has two components i.e. a solvent and a solute.

Solvent

solvent in solution

The component of a solution which dissolves the other component in itself is called solvent. A solvent constitutes the larger component of the solutions.

For example, a solution of sugar in water is solid in the liquid. Here, sugar is the solute and water is the solvent.

Solute

solute in chemistry

The component of the solution which dissolves in the solvent is called solute. The solute is the smaller component of the solution.

For example, a solution of iodine in alcohol known as ‘tincture of iodine’, iodine is the solute. Similarly, in carbonated drinks (Soda water), carbon dioxide gas is the solute.

An aqueous solution is a water that contains one or more dissolved substances. The dissolved substances in an aqueous solution may be solids, gases, or other liquids. Other examples include:
  • Vinegar (acetic acid in water).
  • Alcoholic beverages (ethanol in water).
  • Liquid cough medicines (various drugs in water).
To be a true solution, the mixture must be stable. When sugar is fully dissolved into water, it can stand for an indefinite amount of time, and the sugar will not settle out of the solution. Further, if the sugar-water solution is passed through a filter, it will be unchanged. The dissolved sugar particles will pass through the filter along with the water. This is because the dissolved particles in a solution are very small, usually less than 1nm in diameter. Solute particles can be atoms, ions, or molecules, depending on the type of substance that has been dissolved.

Characteristics of Solution

  • A solution is a homogeneous mixture of two or more substances.
  • The particles of solute in a solution cannot be seen by the naked eye.
  • A solution does not allow beams of light to scatter.
  • A solution is stable.
  • The solute from a solution cannot be separated by filtration (or mechanically).
  • It is composed of only one phase.

Types of Solution

Homogeneous means that the components of the mixture form a single phase. Heterogeneous means that the components of the mixture are of different phases.

The properties of the mixture (such as concentration, temperature, and density) can be uniformly distributed through the volume, but only in the absence of diffusion phenomena or after their completion.

Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids, or solids.

One or more components present in the solution other than the solvent are called solutes. The solutions has the same physical state as the solvent.

Gaseous Mixtures

If the solvent is a gas, only gases (non-condensable) or vapors (condensable) are dissolved under a given set of conditions.

An example of a gaseous solutions is air (oxygen and other gases dissolved in nitrogen).

Since interactions between gaseous molecules play almost no role, non-condensable gases form rather trivial solutions. They are not even classified as solutions in the literature but simply addressed as homogeneous mixtures of gases.

The Brownian motion and the permanent molecular agitation of gas molecules guarantee the homogeneity of the gaseous systems.

Non-condensable gas mixtures (e.g., air/CO2, or air/xenon) do not spontaneously demix, nor sediment, as distinctly stratified and separate gas layers function of their relative density.

Diffusion forces efficiently counteract gravitation forces under normal conditions prevailing on Earth. The case of condensable vapors is different. Once the saturation vapor pressure at a given temperature is reached, vapor excess condenses into the liquid state.

Liquid Solution

If the solvent is a liquid, then almost all gases, liquids, and solids can be dissolved.

Here are some examples:

Gas in Liquid

gas in liquid solution
  • Oxygen in water.
  • Carbon dioxide in water – a less simple example because the solution is accompanied by a chemical reaction (formation of ions). The visible bubbles in carbonated water are not the dissolved gas. But only an effervescence of carbon dioxide that has come out of solution; the dissolved gas itself is not visible since it is dissolved on a molecular level.

Liquid in Liquid

liquid in liquid solution
  • The mixing of two or more substances of the same chemistry but different concentrations to form a constant. (Homogenization of solutions).
  • Alcoholic beverages are basically solutions of ethanol in water.

Solid in Liquid

solid in solid solution
  • Sucrose (table sugar) in water.
  • Sodium chloride (NaCl) (table salt) or any other salt in water, which forms an electrolyte: When dissolving, salt dissociatesinto ions.

Solid Solutions

If the solvent is a solid, then gases, liquids, and solids can be dissolved.

Gas in Solids

gas in solid
  • Hydrogen dissolves rather well in metals, especially in palladium; this is studied as a means of hydrogen storage.

Liquid in Solid

liquid in solid solution
  • Mercury in gold, forming an amalgam.
  • Water in solid salt or sugar, forming moist solids.
  • Hexane in paraffin wax.
  • Polymers containing plasticizers such as phthalate (liquid) in PVC (solid).

Solid in Solid

  • Steel, basically a solution of carbon atoms in a crystalline matrix of iron atoms.
  • Alloys like bronze and many others.
  • Radium sulfate dissolved in barium sulfate: a true solid solution of Ra in BaSO4.

Aqueous Solution

Solutions in water are especially common, and are called aqueous solutions.

Non Aqueous Solution

Non-aqueous solutions are when the liquid solvent involved is not water.

Counter examples are provided by liquid mixtures that are not homogeneous: colloids, suspensions, emulsions are not considered solutions.

Body fluids are examples of complex liquid solutions, containing many solutes. Many of these are electrolytes since they contain solute ions, such as potassium.

Furthermore, they contain solute molecules like sugar and urea. Oxygen and carbon dioxide are also essential components of blood chemistry. Where significant changes in their concentrations may be a sign of severe illness or injury.

Saturated Solutions

saturated solutions

Saturated solutions are solutions dissolving as much solute as it is capable of dissolving at a given temperature. In chemistry, after studying the solutions and properties of the solution, one can understand that a solution can reach a status of saturation.

This state is when the solution has reached a point in which no more solute can be added. The addition of solute after this point would result in a solid precipitate or gas being released. Such a mixture is called a saturated solution.

Preparation of Saturated Solution

A saturated solution is prepared by continuously adding solute to the solution. Until a stage is reached where the solute appears as a solid precipitate or as crystals to form a highly saturated solutions.

  • Consider the process of adding table sugar to a container of water.
  • Initially, the added sugar dissolves as the solution is stirred.
  • Finally, as more sugar has added a point is reached where no amount of stirring will cause the added sugar to dissolve.
  • The last added sugar remains as a solid on the bottom of the container, the solution is saturated.

Unsaturated Solutions

unsaturated solutions

Unsaturated solutions are the ones with a lesser amount of solute than what we require for saturation. Sometimes, by applying external forces like heat energy, you can increase the solubility of the solutes in the solutions.

For the formation of a solutions, we need to add a solute to a solvent. Initially, the solute dissolves in a solvent and makes a uniform solution. Such a solution where solutes dissolve is called an unsaturated solution.

Basically, a solution comprises two different kinds of particles, solutes and solvents. In most cases, water is used as a solvent (which is one of the reasons why water is also called the universal solvent).

Unsaturated solutions can dissolve more solute in them until they reach the saturation point. After reaching the saturation point, solutes will no more get dissolved in the solvent, and these are the unsaturated solutions.

Hence, all the solutions are mostly unsaturated in nature and finally get converted to a saturated solutions by adding solute in them.

Examples of Unsaturated Solutions

We come across various examples of unsaturated solutions in daily life. Some examples of these are given below

  • Salt dissolved in water or even sugar dissolved in water is an unsaturated solution if the quantity of dissolved salt/sugar is below the saturation point.
  • Iced coffee is one more example of an unsaturated solution. Each of the solutes possesses different solubility rules, and also solutes dissolve in the solvent. Those solutions will be considered unsaturated solutions. Tea and the sugar solution is an excellent example of an unsaturated solution due to the reason that they dissolve more amount of sugar in them. Once such solutions reach the saturation point, they get converted to a saturated solution.
  • Gaseous solutions have gas as the solvent, and the solute can either be in a solid-state, liquid state, or even a gaseous state. Air, smoke, and mist are also good examples of unsaturated gaseous solutions.

In an unsaturated solution, the concentration of solute is much lower than its solubility equilibrium. Each solute will have a limit with respect to the specific solvent. Therefore, solutes show a certain value for solubility in the solvent.

Supersaturated Solutions

supersaturated solution

Supersaturated solutions contain more solute than saturated solutions. A supersaturated solution contains more dissolved solute than required for preparing a saturated solutions and can be prepared by heating a saturated solution, adding more solute, and then cooling it gently. Excess dissolved solute crystallizes by seeding supersaturated solutions with a few crystals of the solute.

Example of Supersaturated Solutions

Supersaturated solution contains more dissolved substances than a saturated solution. For example, 40g NaCl in 100ml H2O. The additional 4.0g NaCl remains undissolved.

Supersaturation in Phase Change (Crystallization and Condensation)

  • Physical processes and chemical processes in the vapour melt or solution phase of every system takes place through the formation of three-dimensional 3D nuclei of a new phase and occur only when the medium is supersaturated.
  • The formation of the nuclei is associated with a change in the free energy of the system. In the homogeneous system nuclei ofthe new phase are not formed as soon as the system becomes supersaturated even though thermodynamically such a situation is possible.
  • The system is said to be in a state of metastable equilibrium. And it can remain in that state without attaining the minimum free energy corresponding to the equilibrium state.
  • In other words, in such cases nucleation of the new phase sets in after some period the value depends on such factors as the temperature and pressure of the system. The presence of chemical phases different from the nucleating phase and increased supersaturation level facilitate the process of nucleation of the new phase.
  • However, there is always a supersaturation level when the new phase nucleates instantaneously. That is the new phase precipitates.
  • This supersaturation level corresponds to the upper limit of the state of metastable equilibrium and defines the width of themetastable width.

Ways to Express The Relative Amount of Solute and Solvent in Solution

There are a number of ways to express the relative amounts of solute and solvent in a solution.

Percent Composition (by mass)

We can consider percent by mass (or weight percent, as it is sometimes called) in two ways :

  • The parts of solute per 100 parts of solution.
  • The fraction of a solute in a solution multiplied by 100.

We need two pieces of information to calculate the percent by mass of a solute in a solution :

  • The mass of the solute in the solution.
  • The mass of the solution.

Formula of Percent Composition

Use the following equation to calculate percent by mass :

Percent by mass = Mass of solute/Mass of solvent x 100

Example

Suppose that a solution was prepared by dissolving 25.0g of sugar into 100g of water. The percent by mass would be calculated as follows :

Percent by mass=25g sugar / 125g solution×100% = 20%sugar

Sometimes, you may want to make a particular amount of solution with a certain percent by mass and will need to calculate what mass of the solute is needed.

For example, let’s say you need to make 3.00×103g of a sodium chloride solution that is 5.00% by mass. You can rearrange and solve for the mass of solute.

%by mass = mass of solute / mass of solution×100%
5.00% = mass of solute / 3.00×103g solution×100%
Mass of solute = 150.g

Molarity

molarity of solution

Molarity tells us the number of moles of solute in exactly one liter of a solution. (Note that molarity is spelled with an “r” and is represented by a capital M).

We need two pieces of information to calculate the molarity of a solute in a solution:

  • The moles of solute present in the solution.
  • The volume of solution (in liters) containing the solute.

Formula

To calculate molarity we use the equation:

Molarity = Moles of solute/ Volume of solvent in litres

Example

A solution prepared using 15 g of sodium sulphate. The volume of the solution is 125 ml. Calculate the molarity of the given solution of sodium sulphate.

Solution

Molecular formula of sodium sulphate is Na2SO4.
The molecular formula for water is H2O.
The molecular mass of sodium sulphate is calculated as given below,
M=23×2+32+16×4=142
The number of moles of sodium sulphate in the given question is calculated as,
N = mass in grams / molecular weight
= 15142
=0.106
The volume of the solution is 125 ml.

Expressing the above values in terms of litres,

Volume = 125 / 1000
=0.125
Now, using the formula given above, we calculate the molarity of the given solution.
molarity=number of moles of solute / Volume of solution
Substituting the values, we get,
molarity=0.106 / 0.125
=0.85M
The molarity of the given solution is 0.85M.

Molality

molality of solvent

Molality, m, tells us the number of moles of solute dissolved in exactly one kilogram of solvent. (Note that molality is spelled with two “l”‘s and represented by a lower case m.)

We need two pieces of information to calculate the molality of a solute in a solution :

  • The moles of solute present in the solution.
  • The mass of solvent (in kilograms) in the solution.

Formula

To calculate molality we use the equation :

Molality = Moles of solute/ Mass of solvent in kilograms

Example

Calculate the molality of a solution where 0.5 grams of toluene (C7 H8) is dissolved in 225 grams of Benzene(C6H6). Calculate the moles of given solute.

Solution

Toluene: Molecular weight = C7H8 = 7×12+1×8=92grams/mole
Using the formula: Moles of Toluene = Mass in grams / Molecular weight
=5.0 grams92 grams/mole
=0.054 mole.
So, the mole of toluene is 0.054 mole.
Now calculate the kilogram of solvent.225 grams ofBenzene1000=0.225 kilogram
As the final step, calculate the molality using the formula.
Molality(m)=Moles of Toluene / Mass of Benzene in grams
Molality(m)=0.054 moles / 0.225 kg Molality(m)
=0.24 m

Mole Fraction

mole fraction

The mole fraction, X, of a component in a solution is the ratio of the number of moles of that component to the total number of moles of all components in the solution.

Formula

To calculate mole fraction, we need to know :

  • The number of moles of each component present in the solution.

The mole fraction of A, XA, in a solution consisting of A, B, C, … is calculated using the equation:
XA = Moles of A / Moles of A + Moles of B + Moles of C
To calculate the mole fraction of B, XB, use:
XB = Moles of B / Moles of A + Moles of B + Moles of C

Example

A tank is charged with a mixture of 1.0 x 103 mol of oxygen and 4.5 x 103 mol of helium. Calculate the mole fraction of each gas in the mixture.

Solution

The given parameters are

NHe = 4.5 x 103 mol and NO2 = 1.0 x 103 mol
Mole fraction can be calculated as

XHe= 4.5 x 103 mol / (4.5 x 103 mol + 1.0 x 103 mol)
= 4.5 mol / 5.5 mol = 0.82

XO2 = (2.0 x 103 mol / (4.5 x 103 mol + 1.0 x 103 mol)
= 1.0 x 103/ 5.5 x 103 = 0.18

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