Short Notes: Is Matter Around Us Pure

Elements

Classification of elements :

(A) On the basis of physical states: Solid, Liquid and Gas

(B) Elements can be classified as Metals and Non – Metals

  1. There are 22 non – metals and 93 metals.
  2. Among the metals, only mercury is liquid metal. All other metals are solids.
  3.  Amongst the 22 non – metals : 10 non – metals are solids. They are boron, carbon, silicon, phosphorus, sulphur, selenium, arsenic, tellurium, iodine and astatine.
  4. 1 non-metal, bromine, is a liquid.
  5. Five nonmetals, hydrogen, nitrogen, oxygen, fluorine and chlorine are chemically active gases.
  6. Six non-metals, helium, neon, argon, krypton, xenon and radon are chemically inactive gases. These are also called noble gases or rare gases.

Difference between Compound and Mixture

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Types of Mixture

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Alloys

Alloys are mixtures of two or more metals or  a metal and a non metal and cannot be separated into their components by physical methods. But an alloy is considered a mixture because it shows the properties of its constituents and can have variable composition. e.g. Brass is an alloy having the composition 30 percent Zinc and 70 percent Copper.

Solutions:

A solution is a  homogeneous mixture of two or more substances.  A solution can be of solids or gas. Components of a solution are:

  • Solvent : The component of a solution which is present in large proportion, is called solvent. Usually, a solvent is the LARGER component of the solution. For example : In the solution of copper sulphate in water, water is the solvent. Similarly, in paints, turpentine oil is the solvent.
  • Solute : The component of the solution which is present is small proportion is called solute. For example : In the solution of common salt in water, the common salt is solute. Similarly, in carbonated drinks (soda water), carbon dioxide gas in the solute. Usually, solute is the SMALLER component of the solution.

Example Of  Solutions:

  1. Solid-Solid solution: All alloys are solid solutions of metals. Bell Metal is a solid solution of 80% of copper and 20% of tin, in which copper is the solvent and tin is the solute.
  2. Solid – Liquid solutions : Sugar solution is an example, in which sugar is the solute and water is the solvent. Similarly, common salt solution is an example, in which common salt is the solute and water is the solvent. In case of tincture of iodine, iodine is the solute and ethyl alcohol is the solvent.  
  3. Liquid – Liquid solutions : In case of an alcoholic drink, ethyl alcohol is solute and water is solvent. Similarly, in case of vinegar, acetic acid is solute and water is solvent.
  4. Liquid – Gas solutions : In case of aerated drinks (soda water), carbon dioxide is the solute and water is the solvent.
  5.  Gas – Gas solutions : Air is a homogeneous mixtures of two main gases, i.e., 78% of nitrogen and 21% of oxygen. In this mixture, nitrogen is solvent and oxygen is solute. Similarly, the petrol fed into the engines of automobiles is a mixture of petrol vapor and air.

Types Of Solution:

(i) Saturated solution : A solution, which at a given temperature dissolves as much solute as it is capable of dissolving, is said to be a saturated solution.

(ii) Unsaturated solution : When the amount of solute contained in a solution is less than the saturation level, the solution is said to be an unsaturated solution.

(iii) Super saturated solution : A solution, which contains more of the solute than required to make a saturated solution, is called a super saturated solution.

True Solution:

A solution in which particles of the solute are broken down to such a fine state, that they cannot be seen under a powerful microscope is called a true solution.

(a) Characteristics of a True Solution :

  • A true solution is always clear and transparent, i.e., light can easily pass through it without scattering.
  • The particles of a solute break down to almost molecular size and their diameter is of the order of 1 nm (10-9 m) or less.
  • A true solution can completely pass through a filter paper as particle size of solute is far smaller than the size of pores of filter paper.
  • A true solution is homogeneous in nature.
  • In a true solution, the particles of solute do not settle down, provided temperature is constant. (vi) From a true solution, the solute can easily be recovered by evaporation or crystallization.

(b) Concentration of a Solution (It has no units)

Suspension:

A heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium is known as Suspension. Particles of a suspension are visible to the naked eye. e.g.  Muddy water, in which particles of sand and clay are suspended in water.

Properties of Suspension:

  1. The size of particles is more than 10-5 cm in diameter.
  2. The particles of suspension can be separated from solvent by the process of filtration.
  3. The particles of suspensions settle down, when the suspension is kept undisturbed.
  4.  A suspension is heterogeneous in nature.
  5.  More scattering takes place in suspensions, because of bigger size of particles.

The process of settling of suspended particles under the action of gravity is called sedimentation.

Colloidal Solutions:

A heterogeneous solution in which the particle size is in between 10- cm to 10-5 cm, such that the solute particles neither dissolve nor settle down in a solvent is called colloidal solution.

In a colloidal solution, relatively large suspended particles are called dispersed phase and the solvent in which the colloidal particles are suspended in called continuous phase or dispersing medium.

Examples of colloidal solution are: Blood (It has different particles like RBC, WBC etc), Milk(It has heavy particles like cream etc) , Tooth paste etc.

  Properties Of Colloidal Solution:

  1. The size of colloidal particles is in between 10-7 cm and 10-5 cm.
  2. The particles of a colloidal solution are visible under a powerful microscope.
  3. The particles of a colloidal solution do not settle down with the passage of time.
  4. The particles of a colloidal solution can easily pass through filter paper.
  5. The particles of a colloidal solution scatter light, i.e., when strong beam of light is passed through the colloidal solution, the path of beam becomes visible.
  6.  Colloidal solutions are not transparent, but translucent in nature.
  7. The particles of a colloidal solution are electrically charged.
  8.  The colloidal solutions are heterogeneous in nature.

Tyndall Effect

The phenomenon in which light is scattered by colloidal particles and path of light becomes visible as a Tyndall cone is called Tyndall effect. Some examples of Tyndall effect are

  •  The Tyndall Effect is what causes the sky to appear to be blue. This is because sunlight is scattered as it enters the  Earth’s atmosphere and passes through billions of small particles in the air such as dust, water droplets, and other debris. Once again, because blue has the shortest wavelength of any color of light, it is the color that is predominately seen.

  • The dust in the air when sunlight comes in through a window, or comes down through holes in clouds.

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  • The light of car in the foggy condition.
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Separating the Components of a Mixture:

These are the few methods to separate the components of any mixture:

Evaporation:

It is a type of vaporization of a liquid that occurs from the surface of a liquid into a gaseous phase that is not saturated with the evaporating substance. The other type of vaporization is boiling, which is characterized by bubbles of saturated vapor forming in the liquid phase. Steam produced in a boiler is another example of evaporation occurring in a saturated vapor phase. Evaporation that occurs directly from the solid phase below the melting point, as commonly observed with ice at or below freezing or moth crystals (naphthalene ), is called sublimation.

(click here to know about factors effecting evaporation and application of evaporation)

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Filtration:

Filtration is a physical  operations that separate solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass. The fluid that passes through is called the filtrate. This process work on the basis of the insolubility of the components of the mixture. However, the separation is not complete; solids will be contaminated with some fluid and filtrate will contain fine particles (depending on the pore size, filter thickness and biological activity). The substance which is not soluble and remain behind in the filter paper is known as residue.

There are various methods to do filtration but the more common one is using a filter paper.

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Crystallization:

Crystallization is the (natural or artificial) process by which a solid forms, where the atoms or molecules are highly organized into a structure known as a crystal.  Some of the ways by which crystals form are through precipitating from a solution, melting, or more rarely deposition directly from a gas. Attributes of the resulting crystal depend largely on factors such as temperature, air pressure, and in the case of liquid crystals, time of fluid evaporation. The process is as follow:

  1. The impure substance is dissolved in minimum amount of water.
  2. The solution is filtered to remove impurities.
  3. Then the solution is gently heated in a water bath till a concentrated or a saturated solution of pure substance is formed.
  4. Allow the liquid to cool slowly the crystal of pure substance will form and the impurities will remain in the solution.
  5. Separate the crystals by filtration method and dry.

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Chromatography:

It is a technique used  for the separation of those solutes that dissolve in the same solvent in a very less amount. This process work on the principle that though two or more substance are soluble in the same solvent but their solubility is different. The most common technique of chromatography is paper chromatography. The process is as follow:

  1. Take a thin strip of paper.
  2. Draw a line 3 cm above the bottom with a pencil.
  3. Put a small dot of water soluble ink at the center of the line.
  4. Lower the filter paper into the jar containing  water so that drop of ink on the paper is just above the water level
  5. Leave the setup for some time. You will observe the ink get separated  into different colors.

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Sublimation:

The changing of solid directly to liquid on heating is known as sublimation. Solids which sublimates on heating is known as Sublime. This process is used for the mixture which contain a sublimable volatile components from a non sublimable impurity . Example of sublimation is making pure camphor

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Separation Of Two Immiscible Liquids:

This process work on the principle that two immiscible liquid separate out in layer depending on their densities. The Process occurs as follow:

  1. Take two immiscible liquids. e.g. Water and Kerosene . Pour them in separating funnel and  shake/stir them well.
  2. Leave the apparatus for some time. You will find that water and oil get separated into two layers.
  3. Place a beaker under the stop cork and gently collect the lower layer in the beaker.

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Distillation:

It is a process used for the separating of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points. The process takes place as follow:

  1. Take a mixture of acetone and water
  2. Take the mixture to the distillation flask, fit it with a thermometer.
  3. Heat the mixture slowly.
  4. The acetone vaporize, condenses in condenser and can be collected. Water left behind in the distillation flask.

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Applications:

  1. Salt water is turned into fresh water through distillation.
  2. Various forms of fuel, such as gasoline, are separated from crude oil by distillation.
  3. Alcoholic beverages are made through distillation. The alcohol is boiled off from the rest of the mixture and collected in a concentrated format.

Centrifugation:

It is a technique used for the mixtures having soo small particles which cannot be separated through filter paper. Those were separated with the process of Centrifugation. The process works on the principle that the denser particles are forced to the bottom and the lighter particles stay at the bottom and the lighter particles stay at the top when spun rapidly. A very common example of centrifugation is separation of cream from milk  with the help of churning.

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Applications:

  1. Used in diagnostic laboratories for blood and urine test.
  2. Used in dairies and home to separate butter from cream.
  3. Used in washing machines to squeeze out water from wet clothes.

Separation  Of Gases From Air/Fractional Distillation:

Gas is a homogeneous mixture, having more than two components and can be separated with the help of fractional distillation. In this process liquids are distillated and collected at different levels, A simple fractionating column is being added to the distillation apparatus which contains glass beads which provide surface to vapors to cool and condensate rapidly.

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Applications:

  1. Purification of salt that we get from sea water.
  2. Separation of crystals of alum from impure samples.

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