Written By Shalini Kaveripakam
Last Modified 25-01-2023

Is Matter Around Us Pure: Pure and Impure Substances, Solutions, Separation Techniques

Matter can be found all around us? The chair you’re sitting on, the bed you’re sleeping in, the water or milk you’re drinking, and so on. However, how much of it is truly pure? Is the milk or water you drink is pure? It’s is a mixture of so many substances. So, what is a mixture? Is there only one kind of mixture? Let us learn more information in this article.

Pure Substances

A pure substance is made up of only one kind of molecule or atom. For example, the Sulphur element comprises only one kind of particle (called Sulphur atoms). Therefore, Sulphur is a pure substance.

Similarly, water comprises only one kind of particle (called water molecules). As a result, water is a completely pure substance. Because they only contain one type of particle, all elements and compounds are pure substances.

Impure Substances or Mixtures

A mixture is a material that contains two or different kinds of particles that do not react chemically but are physically mixed in any proportion. Mixtures are impure substances. A mixture has a variable composition, and no definite formula can be given to a mixture. It does not have a fixed boiling point or a fixed melting point. A mixture is further classified into the following types based on the appearance of the matter:

a. Homogeneous mixture
b. Heterogeneous mixture

A substance that is perfectly uniform in its composition throughout the mass is called a homogeneous matter. A substance with different compositions and properties in the different parts of the sample are called a heterogeneous matter. The examples of homogeneous and heterogeneous matters are as follows:

Homogeneous matter: Water, glucose solution, clean air, a solution of sodium chloride in water, etc.
Heterogeneous matter: Muddy water, dusty air, a mixture of sand and sugar, a mixture of sand and sodium chloride, cement, gun powder, etc.

Solution

A solution is a homogeneous mixture of two or more substances. When a solution is a homogenous mixture of two components, it is a mixture of a solute and a solvent. Thus,

\({\rm{Solution}} = {\rm{Solute}} + {\rm{Solvent}}\)

Let us understand what do the terms solute and solvent mean? The solvent is the component of the solution that dissolves the other components (which is usually present in greater amounts). The solute is the part of the solution that dissolves in the solvent (and is usually present in a lesser amount). For example, if a crystal of sugar is added to water in a beaker, it dissolves to form a homogeneous solution.
A solution in which the solute particles are of very small size \(\left( {{\rm{diameter}} < {{10}^{ – 9}}\;{\rm{m}}} \right)\) is called a true solution.

Characteristics of a Solution

A solution is homogeneous in nature.
The particles of solute in solution pass easily through a filter paper.
The diameter of particles in a solution is less than \({{{10}^{ – 9}}\;{\rm{m}}}\)
The particles of a solution are so small that they are not visible even through a high-power microscope.
The solute particles in the solution do not settle on keeping. Therefore, a solution is a stable one.
The properties of solute are retained in solution. For example, a solution of sugar in water is sweet in taste.
A solution is transparent to light and does not scatter light because of its very small particle size.

Learn Classification Of Matter Here

Types of Solutions

When solid things are dissolved in liquids, we normally think of them as solutions. Although most solutions are created by dissolving solids in liquids, this is not always the case. Solids in solids, solids in liquids, liquids in liquids, gases in liquids, and gases in gases can all be used to make solutions. Please keep in mind that as long as the mixture is homogeneous, the term “solution” applies.

The following are examples of different sorts of solutions:

Solid solution in solid: Metal alloys in solid solutions are solid. Brass, for instance, is a copper zinc solution. Molded Zinc is combined with molten copper and the resultant mixture is then cooled down.
Liquid Solid Solution: This is the most common type of solution. Solids are known as solutions in liquid solutions such as sugar and salt. An iodine solution in alcohol known as ‘iodine tincture’ is also a ‘solid solution’ in a liquid. That is because the solution that is dissolved as a solvent in a liquid (alcohol) contains a solid (iodine).
The liquid in a Liquid Solution: Vinegar is an acetic acid (ethanoic acid) solution in water. It’s a liquid within a liquid solution.
The Solution of a Gas in a Liquid: Soda water is a carbon dioxide gas solution in water. It’s a gas dissolved in a liquid solution.
The Solution of a Gas in a Gas: Air is a mixture of gases such as oxygen, argon, carbon dioxide, water vapour, and others suspended in nitrogen gas. All other gases are solutes, and nitrogen is the solvent in air.
Solution of Gas in Solid: Example: Solution of hydrogen in palladium.
Solution of Liquid in Gas: Example: Chloroform mixed with nitrogen gas.
Solution of Solid in Gas: Example: Camphor in nitrogen gas.
Solution of Liquid in a Solid: Example: Amalgam of mercury with sodium.

The Concentration of a Solution

It is the amount of solute present in a given amount either by mass or by volume of solution, or it is the amount of solute dissolved in a given mass or volume of solvent.

The concentration of a solution = amount of solute/amount of solution.

Ways of Expressing the Concentration of Solution

Mass by the mass percentage of a solution \( = \frac{{{\rm{Mass}}\,{\rm{of}}\,{\rm{solute}}}}{{{\rm{Mass}}\,{\rm{of}}\,{\rm{solution}}}} \times 100\)

Mass by volume percentage of a solution \( = \frac{{{\rm{Mass}}\,{\rm{of}}\,{\rm{solute}}}}{{{\rm{Volume}}\,{\rm{of}}\,{\rm{solution}}}} \times 100\)

Parts per million or parts per billion

Parts per million is used for expressing the concentration of trace amount of substance present in the total amount of solution.

It can be calculated as:

\({\rm{ppm}} = \left( {{\rm{mass}}\,{\rm{of}}\,{\rm{solute}}/{\rm{mass}}\,{\rm{of}}\,{\rm{solution}}} \right) \times {10^6}\).

\({\rm{ppb}} = \left( {{\rm{mass}}\,{\rm{of}}\,{\rm{solute}}/{\rm{mass}}\,{\rm{of}}\,{\rm{solution}}} \right) \times {10^9}\).

Saturated and Unsaturated Solutions

At a certain temperature, there is a concentration at which no more solute will dissolve in a solution. The solution is said to be saturated at that temperature at this moment. A saturated solution is one in which no additional solute can be dissolved at a specific temperature.

An unsaturated solution is one in which a greater amount of solute may be dissolved at a given temperature.

Also, there is a solution called a supersaturated solution. Such a solution contains more solute than required to prepare a saturated solution at any fixed temperature.

Suspensions

It is a heterogeneous mixture in which solid particles are insoluble in a solvent and visible to the naked eye.
Example: chalk powder in water, sulphur powder in water, dust storm, muddy river water.

Properties of Suspension

Suspension is a heterogeneous mixture
The particles of suspension do not pass through filter paper. Therefore, they can be separated by filtration.
The particles are visible with the naked eye or with the help of a simple microscope.
The particles of suspension may settle down on keeping for some time due to gravity.
The particle size is greater than \(1000\,{\rm{nm}}\), i.e., \({10^{ – 6}}\,{\rm{m}}\).
A suspension is opaque to light.

Colloidal Solution

The solution in which particle size is between \(1\,{\rm{nm}}\) and \(1000\,{\rm{nm}}\). The particles are smaller than that of particles in suspension.
The component present in a smaller proportion is the dispersed phase while the one present in the greater proportion is called dispersion medium. Milk is an example of the emulsion of oil in water. Disperse phase is oil (liquid fat particles). The dispersion medium is water.

Classification of colloidal solution

The colloidal solution can be classified into eight types given below, depending upon the state of the two phases, namely the dispersed phase and the dispersion medium.

Properties of Colloids

Some characteristic properties of colloids are described below:

A colloid or sol is heterogeneous in nature.
The size of particles in colloid lies between \(1\,{\rm{nm}} – 1000\,{\rm{nm}}\) in diameter, which is bigger than those in true solution but smaller than those in suspension.
Colloidal particles can easily pass through the pores of filter paper. Therefore, colloidal particles cannot be separated by filtration.
The particles of colloids can be seen under a powerful microscope.
Colloids are unstable and stabilized by a suitable stabilizer. The colloidal particles try to come closer to each other and settle down.
Tyndall effect: Light scattering by colloidal particles is called the Tyndall effect.

When an intense beam of light is passed through a colloidal solution kept in the darkroom, the path of the light beam through the colloidal becomes visible.
If the light is passed through the true solution, the path is not illuminated, whereas, in a colloidal solution, it gets illuminated.

Causes of Tyndall effect

It is due to the scattering of light by colloidal particles. This effect can be observed in theatres when a beam of light is thrown on the screen; we observe the light path clearly visible because dust particles in the air scatter light. Shafts of light are visible coming through trees in the forest due to the Tyndall effect. This effect can also be observed when sunlight passes through a dense forest. The sky is blue due to the scattering of light by colloidal particles due to the Tyndall effect.

Examples of colloidal solution: Blood, milk, soap solution, Ink, egg albumin in water, starch in water, gum in water, gold sol, silver sol, dust particles in the air.

Separating the Components of a Mixture

By now_, it is clear that most of the substances available in our surroundings are not chemically pure. The method of separation used depends on the differences in the properties of the components of the mixture. As far as heterogeneous mixtures are concerned, simple physical methods can be used for separating their components. However, some mixtures require special methods for separating their components.

Methods Used for Separating the Components of a Mixture

There are various methods employed for separating the components of a mixture. But as discussed before, the method used depends on the difference in the properties of the components of the mixture. Before giving the details of these methods, let us see the different types of separations that we come across most often.

Different physical techniques like sublimation, Magnetic separation, Filtration, Centrifugation, Evaporation, Crystallisation, Chromatography, Distillation, Fractional distillation, and Separating funnel are often employed to separate the contents of mixtures. More than one of these procedures may be employed to separate a mixture in some instances.

To discover how to separate mixtures, we’ll look at the following three scenarios:

1. Separation of a Solid-Solid Mixture

One of the following procedures can be used to separate all mixtures involving two solid substances:

(i) By using a suitable solvent
(ii) By the process of sublimation
(iii) A magnet is used to separate two objects

(i) Separation with a Suitable Solvent

In some circumstances, one component of a mixture is soluble in a liquid solvent while the other is not. This variation in solubilities can be exploited to separate the constituents of a mixture. Sugar, for example, is soluble in water but not in sand, so a mixture of sugar and sand can be separated using water as a solvent.

(ii) By the Process of Sublimation

Sublimation is the process of a solid converting straight to vapours on heating and vapours converting to solids on cooling. The solid substance that sublimates is referred to as ‘sublime.’ Sublimation is a technique for separating components from a mixture that sublime when heated. The following example will demonstrate this;

To Separate a Common Salt and Ammonium Chloride Mixture

Heating causes ammonium chloride to be sublime. However, heating does not cause common salt to be sublime. Sublimation allows us to separate ammonium chloride from a mixture of ‘common salt and ammonium chloride.’ This is accomplished in the following manner.

(iii) A Magnet is used to Separate two Objects

Iron is attracted to a magnet. Iron’s ability to extricate itself from a mixture is based on this feature. If a combination contains iron as one of its constituents, a magnet can be used to separate it. A magnet can separate a mixture of iron filings and sulphur powder. A magnet attracts (and sticks to) iron filings, while a magnet does not attract sulphur.

2. Separation of Solid-Liquid Mixtures

One of the following techniques separates all mixtures involving a solid and a liquid:

(i) By filtration
(ii) By centrifugation
(iii) By evaporation
(iv) By crystallization
(v) By chromatography
(vi) By distillation

(i) By Filtration

Filtration is the technique of removing insoluble materials from a liquid using filter paper. Filtration is a technique for separating soluble and insoluble compounds from liquids.

Filtration separates a mixture of chalk and water. Clearwater flowed through the filter paper and is collected as filtrate when the chalk and water mixture is put on the filter paper fixed in a funnel. As a residue, the chalk particles remain on the filter paper.

(ii) By Centrifugation

Centrifugation is a technique for separating suspended particles from liquids that involves spinning the mixture at high speed in a centrifuge.

Blood is made up of a mixture of blood cells suspended in a liquid known as plasma. Centrifugation can separate blood into blood cells and plasma. The blood cells at the bottom and plasma at the top of the centrifuge tube in the above photograph have been separated by centrifugation.

(iii) Evaporation

Evaporation is the transformation of a liquid into vapours (or gas). When a solid substance has dissolved in water, evaporation is utilised to separate it (or any other liquid).

The technique of evaporation can be used to separate common salt dissolved in water. This is accomplished as follows: In a china dish, a common salt and water solution is placed and gradually heated on a stove [see Figure (a)]. Water vapours will form and escape into the atmosphere due to the water in the salt solution. When the water in the common salt solution evaporates, the common salt remains as a white solid in the china dish [see Figure (b)].

(iv) Crystallization is a Method of Purification

Crystallization is the process of cooling a heated, concentrated solution of a chemical to form crystals. The crystallization procedure is used to create a pure solid product from an impure sample.

(v) Chromatography

Chromatography is a method for separating two (or more) dissolved solids that are present in very small amounts in a solution. There are many different types of chromatography, but paper chromatography is the simplest.

(vi) Separation by Distillation

The conversion of a liquid into vapours by heating followed by condensing the vapours by cooling to obtain the pure liquid is called distillation.
Applications of simple distillation
1. Separation of a mixture of propanone (boiling point \(56.5\,^\circ {\rm{C}}\)) and water (boiling point \(100\,^\circ {\rm{C}}.\))
2. Separation of a mixture of propanone (boiling point \(56.5\,^\circ {\rm{C}}\)) and ethanol \(\left( {78\,^\circ {\rm{C}}} \right).\)

Separating Pure Water from a Solution of Common Salt by Distillation
Take about \(500\,{\rm{mL}}\) of an aqueous solution of common salt in a distillation flask and heat the distillation flask on a sand bath by a Bunsen burner. The solution boils to produce water vapours that pass through the condenser and get condensed to form water drops collected in a receiver. This water obtained is pure water. When a small quantity of solution is left in the distillation flask, stop the heating.

3. Separation of Mixture of Two (Or more) Liquids

All the mixtures containing two (or more) liquids can be separated by one of the following two methods:

(i) By the Process of Fractional Distillation

This process is used for the separation of those liquids which have a difference in their boiling point is less than \(25\,^\circ {\rm{C}}.\) For example, various fractions of petroleum are obtained by fractional distillation. Different gases from the air are also obtained by fractional distillation.
The apparatus is shown in the figure below. It makes use of fractionating column fitted over the distillation flask, which gives the effect of repeated distillation.
A fractionating column is a glass tube packed with glass beads. The beads provide a surface for the vapours to cool and condenses so that different components can be separated very easily in pure form, even if their boiling points are close to each other.
It is the process of obtaining pure substances from impure substances by cooling a hot saturated solution of that substance in a suitable solvent.

Separation of Ethyl alcohol and Water:
A mixture of ethanol and water is taken in a distillation flask fitted with a fractionating column. The mixture is heated to about \(78\,^\circ {\rm{C}}\) that is the boiling point of the ethanol. The ethanol begins to boil. A mixture of ethanol and water vapours rises the column. Since water has a higher boiling point than ethanol, it condenses back into the flask.
In contrast, the ethanol vapours move up the column into the condenser, gets condensed into liquid ethanol and is collected in the beaker. When all ethanol is distilled over, the temperature reading on the thermometer rises to \(100\,^\circ {\rm{C}}\), i.e., the boiling point of water. The water begins to boil, and the vapours rise up the column and enter the condenser, where it gets condensed and collected in another beaker.

(ii) By Using a Separating Funnel

A mixture of two immiscible liquids can be separated using a separating funnel.
Separating two immiscible liquids like water and oil
Take \(500\,{\rm{ ml}}\) of vegetable oil and water mixture in a \(500\,{\rm{ml}}\) separating funnel fitted with a stopper. Clamp the separating funnel on an iron stand and allow the separating funnel to stand undisturbed for some time. Two separate layers of water and oil are formed. Oil is lighter than water forms the upper layer. Remove the stopper from the separating funnel, open the stopcock of the separating funnel and collect the lower layer of water in a beaker. Close the stopcock when the oil reaches the stopcock.
Two immiscible liquids separate in different layers due to the difference in their densities, and hence, such liquids can be separated using a separating funnel.

Important Questions on is Matter Around Us Pure

Q.1. \(25\;{\rm{mL}}\) of ethanol is present in \(150\;{\rm{mL}}\) of its aqueous solution. What is the concentration of the solution?
Ans: \({\rm{Volume}}\,{\rm{of}}\,{\rm{ethanol}} = 25\;{\rm{mL}}\)
\({\rm{Volume}}{\mkern 1mu} \,{\rm{of}}\,{\rm{solution}} = {\rm{Volume}}{\mkern 1mu} \,{\rm{of}}\,{\rm{ethanol}} + {\rm{Volume}}{\mkern 1mu} \,{\rm{of}}{\mkern 1mu} {\rm{water}}\)
Volume by volume percentage of ethanol in solution
\({\rm{ = }}\frac{{{\rm{Volume}}\,{\rm{of}}\,{\rm{ethanol}}}}{{{\rm{Volume}}\,{\rm{of}}\,{\rm{solution}}}} \times 100\)
\( = \frac{{25}}{{150}} \times 100 = 16.67\% ({\rm{v}}/{\rm{v}})\)

Q.2. It is not possible to distinguish particles of a solute from that of the solvent in a solution. Explain.
Ans: The size of the solute particles in the solution is very small \(\left( { < {{10}^{ – 9}}\;{\rm{m}}} \right)\) and the solute particles get entrapped in the space between the solvent particles. As a result, the solute and solvent particles cannot be distinguished in a solution.

Q.3. Which separation techniques will you apply for the separation of the following mixtures?
Ans:

1. Sodium chloride from its solution in water.
2. Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
3. Small pieces of metal from the engine oil of a car.
4. Benzene from a mixture of benzene and methylbenzene.
5. Different pigments from an extract of flower petals.
Ans: 1. Evaporation 2. Sublimation 3. Magnetic separation technique 4. Distillation 5. Chromatography.

Summary

Anything that has mass and occupies space is considered as matter. So, the matter is everything, including your clothes, food, etc. All matters are not of the same kind. Matter can be classified into one of two categories: mixtures or pure substances.

A pure substance is simply a pure form of matter that is it contains only one type of atom or molecule. On the other hand, a mixture contains a combination of different atoms or molecules and is; therefore, a pure substance refers to either an element or a compound but not a mixture, as a substance always has a definite composition. In this article, we learned about mixtures, pure substances, solutions and different separation methods.

Frequently Asked Questions (FAQs) on Is Matter Around us is Pure

Q.1. How can you change a saturated solution to an unsaturated solution without adding any more solvent to it?
Ans: Heat can turn a saturated solution into an unsaturated one (without adding solvent). When a saturated sugar solution is heated to a higher temperature, it begins to dissolve additional sugar.

Q.2. Which are the solute and the solvent in the tincture of iodine?
Ans: A solution of iodine in alcohol known as tincture of iodine has iodine(solid) as the solute and alcohol(liquid) as the solvent.

Q.3. What is the mass per cent of the solution?
Ans: The concentration of a solution by mass per cent may be defined as the number of parts by mass of solute per \(100\) parts by mass of solution. Thus, the concentration of the solution can be calculated by this method using the following formula,
Mass by the mass percentage of a solution \( = \frac{{{\rm{Mass}}\,{\rm{of}}\,{\rm{solute}}}}{{{\rm{Mass}}\,{\rm{of}}\,{\rm{solution}}}} \times 100\)

Q.4. Give three properties of colloid. Differentiate between a true solution and a colloid.
Ans: The three properties of colloid are:

A colloid or sol is heterogeneous in nature.
The size of particles in colloid lies between \(1\,{\rm{ nm}} – 1000\,{\rm{ nm}}\) in diameter, which is bigger than those in true solution but smaller than those in suspension.
Colloidal particles can easily pass through the pores of filter paper. Therefore, colloidal particles cannot be separated by filtration.

Difference between a true solution and a colloid.

	Property	True solution	Colloidal solution
1.	Nature	Homogeneous	Heterogeneous
2.	Particle size	\( < {10^{ – 9}}\;{\rm{m}}\)	\({10^{ – 9}}\) to \({10^{ – 6}}\;{\rm{m}}\)
3.	Appearance	Transparent	Generally transparent but may also show translucence.
4.	Visibility	Particles are neither visible with the naked eye nor under a microscope.	Particles are not visible to the naked eye but are visible under a powerful microscope.
5.	Settling of particles under gravity	No settling	Very slow settling. Reasonable settling under high-speed centrifugation.
6.	Filterability	Particles pass through filter paper and parchment paper.	Particles do not pass through parchment paper but pass through filter paper.
7.	Brownian movement	Not observed	Observed
8.	Tyndall effect	Does not exhibit the Tyndall effect.	Exhibits Tyndall effect.

Q.5. What do you observe when an aqueous sugar solution is heated to dryness?
Ans: When the water in the aqueous sugar solution is heated, it evaporates first. The sugar will char when the solution is heated to dryness.

Q.6. What are the two components of a colloidal solution?
Ans: The components of a colloidal solution are the dispersed phase and dispersed medium.

Study Physical Nature of Matter Here

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