Class 9 Is Matter Around Us Pure Short Notes
Introduction
A mixture is a combination of two or more pure substances that are not chemically bonded.
The components of a mixture retain their individual properties and can be separated by physical means.
Mixture And Its Type
A mixture is a combination of two or more pure substances that are not chemically bonded.
→ Types of Mixture
- Homogeneous Mixtures: Mixtures that have uniform composition throughout, like salt-water, or air.
- Heterogeneous Mixtures: Mixtures with non-uniform composition, like sand in water or oil and vinegar.
Solution And Its Properties
A solution is a homogeneous mixture. In which one or more substances are dissolved in another substance. In a solution, there is solvent and solute which are mixed together.
→ Type Of Solution
(i) Solvent
(ii) Solute
(i) Solvent: The major component in a solution is the solvent, which is the one dissolving the other component(s) known as solute(s).
(ii) Solute : A solute is the one that is being dissolved in the solution by a solvent. Solute is relatively less in comparison to the amount of solvent present. Solutes can be any physical state that is either a solid, a liquid, or a gas.
→Properties of solution
Homogeneity: The solutions are uniformly composed throughout.
Particle Size: Particles of solute in solution are extremely minute, typically on the order of less than 1 nanometer.
Concentration: Amount of solute dissolved in solvent expressed in various units (e.g., molarity, molality).
Colligative Properties: Properties such as boiling point elevation and freezing point depression are colligative. They depend upon the concentration of the solute.
Electrical Conductivity: Some solutions will conduct electricity when there are ions present in them.
Concentration Of Solution
The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution. Also, the amount of solute dissolved in a given mass or volume of solvent is called concentration of solution.
Saturated and Unsaturated Solutions:
- Saturated solution: A solution that contains the maximum amount of solute that can be dissolved in the solvent at a given temperature.
- Unsaturated solution: A solution that can still dissolve more solute.
Concentration of Solution
- Concentration is the amount of solute present in a given amount of solution or solvent.
- Common expressions of concentration include:
- Qualitative: Dilute and Concentrated
- Quantitative: Mass percentage, Volume percentage
→ Two methods of finding concentration of solution:
(i) Mass by mass percentage of a solution = (Mass of solute/Mass of solution) ×100
(ii) Mass by volume percentage of a solution = (Mass of solute/Volume of solution) ×100
Suspension And its Properties
A suspension is a heterogeneous mixture where the particles of a substance are dispersed throughout another substance. The particles in a suspension are larger and can be seen with the naked eye or under a microscope.
→Properties Of Suspension
- Suspensions are heterogeneous mixtures, with the suspended particles clearly visible.
- The particles in a suspension are relatively larger and fall within the size range of 1000 nm to 1 mm.
- The suspended particles eventually settle down over time because of the effect of gravity.
- Suspensions can be separated by filtration, in which the suspended particles are retained on the filter paper.
- Suspensions are less stable compared to solutions since the suspended particles tend to aggregate and settle over time.
Colloidal Solution And its Properties
A colloidal solution, also called a colloid, is a type of heterogeneous mixture in which particles of a substance are dispersed and suspended throughout another substance. →Properties of Colloidal Solution
• A colloid is a heterogeneous mixture.
• The size of particles of a colloid is too small to be individually seen by naked eyes.
• Colloids are big enough to scatter a beam of light passing through it and make its path visible.
• They do not settle down when left undisturbed, that is, a colloid is quite stable.
Separation of the Constituents of a Mixture of a Mixture
Different methods of separation are used to get individual components from mixture. Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration etc.
Obtaining coloured components from blue/black ink
To separate the colored components from blue/black ink:
- Use paper chromatography.
- Place a drop of ink on a paper strip.
- Suspend the paper in a solvent (e.g., water, ethanol).
- Allow the solvent to travel up the paper.
- Different ink components will settle into colored bands.
- Observe the separated colors to determine what the ink is made of.
Separation of cream from milk
Milk is a heterogeneous mixture that has fat globules (cream) and other elements such as proteins, lactose, and minerals. To separate the cream,
- Let the milk stand for a while without being disturbed.
- The fat globules in the milk float to the top and settle as a cream layer.
- This cream layer can be separated by skimming or decanting afterwards.
The basic steps are:
- Allowing the milk to stand to let the cream rise.
- Separating the cream layer from the rest of the milk.
This simple physical method exploits the difference in density between the fat-rich cream and the rest of the milk constituents to effect the separation.
Separating two immiscible liquids
When two liquids that do not mix, such as oil and water, are mixed together, they form distinct layers. To separate them:
- Pour the mixture into a separating funnel.
- Allow the layers to settle and separate.
- Drain the denser liquid, usually the water layer, from the bottom of the funnel.
- The less dense liquid, usually the oil layer, remains in the funnel.
This simple mechanical process takes advantage of the differences in densities between the two liquids that are immiscible to accomplish separation.
The major steps include:
- Utilization of a separating funnel to hold the mixture.
- Allowance for the liquid layers to separate according to differences in densities.
- Drainage of the denser liquid at the bottom.
- Retention of the less dense liquid in the funnel.
This method works effectively and is common for the purification or separation of immiscible liquid components.
Sublimation
Sublimation is the direct transformation of a solid substance into the gaseous state, without passing through the liquid state.
Some key points about sublimation:
1. It is a physical process.
2. Examples: Camphor, naphthalene, dry ice (solid CO2).
3. The solid directly converts to gas upon heating, bypassing the liquid phase.
4. The reverse process is called deposition, where the gas directly forms the solid.
5. Sublimation is applied in the purification of some solid materials.
Chromatography
Chromatography is a method of separating and identifying the constituents of a mixture.
Key points:
- It is a physical separation method.
- The mixture is dissolved in a solvent and passed through a stationary phase.
- The constituents separate due to their different affinities towards the stationary phase.
- Types: Paper chromatography, thin-layer chromatography (TLC), column chromatography.
- Applied in the identification and purification of chemical compounds.
Distillation
Distillation is a technique used to separate the components of a liquid mixture based on their differences in boiling points.
Key points:
- It is a physical separation technique.
- The liquid mixture is heated, and the components with lower boiling points vaporize first.
- The vapors are then cooled and condensed to obtain the separated components.
- Used to purify liquids and separate miscible liquids.
- Examples: Purification of alcohol, separation of components in crude oil.
Fractional distillation
It is a distillation technique, whereby a miscible liquid mixture is separated in such a mixture which has almost close boiling points.
Key points
- It is one of the processes of distillation.
- A mixture is heated within a fractionating column having many sections or trays.
- Vapor rises along with the column height and gets condensed at varying heights according to its boiling points.
- Components of lower boiling point are collected on top, and the higher boiling components are collected at the bottom.
- It results in a better separation compared to simple distillation.
- Used for the purification of crude oil for the production of different fuels and other petroleum products.
Crystallization
Crystallization is the process of purifying solid impurities by changing them from solution or melt to a crystalline solid state.
Important points:
- It is a physical separation technique.
- The solute is dissolved in a suitable solvent, and the solution is then cooled or the solvent is evaporated
- As the solution becomes supersaturated, the solute crystallizes out in the form of pure crystals
- The crystals are then separated from the mother liquor (remaining solution) by filtration
- Used considerably to purify chemicals, minerals, and other solid substances
- Examples: Purification of salt, sugar, and certain medicines.
Physical and Chemical change
Physical Change:
A physical change is that change in the physical properties of a substance, but there is no change in its chemical composition.
Examples: Boiling of water, melting of ice, tearing of paper.
In a physical change, the chemical bonds between atoms are not broken.
Chemical Change:
A chemical change is that change in which the chemical composition of a substance is altered, and new substances with different properties are formed.
Examples: Burning of wood, rusting of iron, photosynthesis.
In a chemical change, the chemical bonds between atoms are broken and rearranged to form new bonds, leading to
What are the Types of Pure What are the Types of Pure Substances?
On the basis of their chemical composition, substances can be classified either as elements or compounds.
Element:
An element is a pure substance that cannot be broken down into simpler substances by chemical means.
Key points about elements:
- Elements are the basic building blocks of matter.
- There are 118 known elements, out of which 92 are naturally occurring.
- Elements are broadly classified into three categories:
- Metals (e.g., iron, copper, gold)
- Non-metals (e.g., oxygen, nitrogen, carbon)
- Metalloids (e.g., silicon, germanium, arsenic)
- Elements are characterized by a unique set of physical and chemical properties, which include melting point, boiling point, and reactivity.
- Elements are placed in the periodic table according to atomic number and chemical properties.
- A tabular arrangement of elements in order of atomic number and chemical properties is the periodic table.
- The periodic table is used in predicting the chemical behavior of the elements and compound formation.
Some examples of elements are as follows:
Hydrogen (H)
Oxygen (O)
Carbon (C)
Sodium (Na)
Chlorine (Cl)
Gold (Au)
Compound: A compound is a substance composed of two or more elements, chemically combined with one another in fixed ratio.