Matter Around us Pure Class 9 Notes – Here, we have summarized and created revision notes for Class 9 Science Chapter 2. These CBSE notes include key points, revision notes, and diagrams covering all aspects of Chapter 2, “Is Matter Around Us Pure” from the science curriculum taught in Class 9.
Matter Around us Pure Class 9 Notes
What is pure substance?
A pure substance is a material with a fixed and unique composition and properties, either an element or a compound. Pure substances are homogeneous, meaning they have a uniform composition throughout.
- Pure substances are single-entity materials, either elements or compounds.
- They have a constant boiling and melting point.
- Pure substances are made up of only one type of atom or molecule, such as metals, nonmetals, or metalloids.
- Elements are pure substances that cannot be broken down into simpler substances chemically, and include substances like hydrogen, oxygen, gold, silver, etc.
- Compounds are pure substances formed from chemical combination of two or more elements, and have properties different from their constituent elements, like water (H2O) formed from hydrogen and oxygen.
- Pure substances take part in chemical reactions to produce predictable results, such as Diamond or Carbon Dioxide.
What is Element?
An element is a fundamental component of matter. It is a pure substance with just one type of atom and cannot be chemically broken down or changed into another substance. The periodic table of elements contains 118 elements, each of which has particular chemical and physical characteristics. In the periodic table, each element is represented by a unique symbol consisting of one or two letters.
- Hydrogen (H)
- Helium (He)
- Lithium (Li)
- Beryllium (Be)
- Boron (B)
- Carbon (C)
- Nitrogen (N)
- Oxygen (O)
- Fluorine (F)
- Neon (Ne)
Elements are categorized into three types.
Metals – Metals are solid materials characterized by their hardness, shiny appearance, malleability (ability to be shaped), fusibility (ability to be melted), ductility (ability to be drawn into thin wires), and good electrical and thermal conductivity. Examples of metals include aluminum, copper, iron, tin, and gold.
Nonmetals – Nonmetals are brittle, difficult to shape and inefficient heat and electricity conductor materials. Non-metals include things like carbon and boron.
Metalloids – Metalloids are elements with properties of both metals and non-metals. Examples of metalloids include arsenic, antimony, boron, silicon, germanium, and tellurium.
What is Compound?
Compounds are substances made up of two or more elements combined in a specific, fixed ratio. They have unique properties distinct from their individual elements. Compounds can only be separated into their constituent elements through chemical reactions, not physical means. Water is an example of a compound made of hydrogen and oxygen.
Difference between Element and compounds
|Made up of a single type of atom
|Made up of two or more different elements chemically bonded together.
|Have unique properties
|Properties different from those of its individual elements
|Cannot be broken down into simpler substances by chemical means
|Can be broken down into simpler substances through chemical reactions.
|Examples: Hydrogen, Iron, Gold
|Examples: Water (H2O), Salt (NaCl), Methane (CH4)
What is mixture?
A mixture is a combination of two or more substances that are physically blended together, but do not chemically combine to form a new substance. The substances in a mixture retain their individual chemical and physical properties and can be separated by physical method. Examples of mixtures include air, salt water, and orange juice.
Some common properties of mixtures are –
- There are two types of mixtures: homogeneous (uniformly mixed) and heterogeneous (not uniformly mixed).
- The properties of the individual substances in a mixture are retained and do not change.
- Mixtures do not form new compounds, they simply physically blend the substances together.
- Elements in a mixture can be separated by simple physical processes, such as filtration or distillation.
- Mixtures do not have a fixed melting and boiling point, as they can have a range of temperatures at which they change state.
Types of Mixture
There are two main types of mixtures:
- Homogeneous mixtures: In a homogeneous mixture, the composition is uniform throughout the mixture and the different components are not distinguishable. Examples include salt water, air, and sugar water.
- Heterogeneous mixtures: In a heterogeneous mixture, the composition is not uniform and the different components are visibly distinguishable. Examples include a fruit salad, a mixture of sand and water, and a chocolate chip cookie.
Physical vs Chemical Changes
Physical changes: Physical changes involve a change in a substance’s physical properties, such as size, shape, or state (solid, liquid, or gas), without any change to its chemical composition. Examples of physical changes include melting, freezing, cutting, and grinding.
Chemical changes: Chemical transformations are processes that result in new compounds with properties and composition that differ from the original substances. A release or absorption of energy, such as heat, light, or sound, usually occurs. The chemical processes of burning, rusting, and digestion are a few examples.
What is Solutions and their properties
A homogenous mixture of two or more substances is referred to as a solution. The substances in a solution are evenly mixed and cannot be easily separated by physical means. Solutions, which can be liquids, gases, or solids, have unique properties that are distinct from their individual components.
Properties of solutions –
- Composition: Uniformity in composition and variable solute concentration characterise a solution.
- Solubility: Temperature and pressure affect a solute’s ability to dissolve in a solvent. In some solvents compared to others, some solutes are more soluble.
- Transparency: Solutions frequently have this quality, permitting light to pass through.
- Conductivity: Electricity conductivity varies widely between different solutions. The concentration of ions in a solution has an impact on its capacity to conduct electricity.
- Viscosity: Depending on the solute concentration and the kind of solvent, solutions can have a range of viscosities.
- Osmosis: Osmosis is the process by which solvent molecules migrate from a location of higher concentration to a region of lower concentration through a membrane that is selectively permeable.
Any combination of two or more elements in which there is at least one metal is known as an alloy. They are uniform and possess unique qualities from the constituent parts. Brass, bronze, and steel are a few examples of alloys. Steel is an alloy comprised of iron and carbon (made from copper and zinc).
The term “solubility” describes the maximum amount of a solute that dissolve in a solvent to form a homogeneous solution under a specific given temperature and pressure. The equilibrium between the energetic attraction between the solute and solvent particles and the propensity of the solute particles to disperse in the solvent determines it. Temperature, pressure, and the presence of other solutes in the solution are just a few examples of the variables that might affect solubility.
Types of solutions based on the concentration of the solution
There are several types of solutions based on the concentration of the solute:
- Dilute Solution – A solution with very little solute and a lot of solvent.
- Concentrated Solution – A solution with a lot of solute and less solvent.
- Saturated Solution – A solution where the solute has reached its maximum limit and can’t dissolve any further at a specific temperature and pressure.
Ways of representing the concentration of a solution
There are several way where concentration of a solution can be represented –
a. Mass by mass percentage of a solution = (Mass of solute / Mass of solution) × 100
b. Mass by volume percentage of a solution = (Mass of solute/ volume of solution)×100
What is a suspension and its properties
A suspension is a sort of mixture where the solute particles are suspended in the solvent without dissolving. The particles will settle to the bottom of a container if they are left undisturbed for a while and are large enough to be seen with the unaided eye. Mud or sand suspended in water are two examples of suspensions.
A suspension is a heterogeneous mixture of solid particles dispersed in a liquid or gas. The properties of suspensions include:
- Particles are not dissolved, but are visibly suspended in the mixture.
- Particles settle to the bottom of the container over time due to gravity.
- The particles in a suspension can scatter light, making the mixture appear cloudy or turbid.
- The particle size and distribution can affect the physical properties of a suspension, such as viscosity and conductivity.
- Suspensions are not homogeneous and their properties can vary depending on the location within the mixture.
- Filtering or allowing the mixture to stand for a period of time can separate the solid particles from the liquid or gas.
What is Colloidal Solution and its properties
In a colloidal solution, a solute’s particles are uniformly distributed throughout a solvent to create a homogeneous combination. A colloidal solution contains particles that are between the size of those in a real solution and those in a suspension. The combination appears cloudy or turbid because the particles, albeit too minute to be seen with the human eye, are large enough to scatter light. Milk, a dispersion of fat particles in water, is an illustration of a colloidal solution.
The key properties of colloidal solutions include:
- Tyndall effect: Colloidal solutions scatter light, giving them a cloudy appearance. This is known as the Tyndall effect.
- Brownian motion: Particles in a colloidal solution move randomly due to collisions with solvent molecules. This is called Brownian motion.
- Stability: Colloidal solutions can be either stable or unstable, depending on the forces holding the dispersed particles in suspension. If the forces are strong enough to keep the particles from settling, the colloid is stable. If not, it is unstable.
- filterability: Colloidal solutions can pass through a filter that will retain larger particles.
- Surface tension: The dispersed particles in a colloidal solution often have a significant effect on the surface tension of the dispersion medium.
Difference between suspension and colloidal soluation
|Dispersed particles are large and visibly suspended
|Dispersed particles are intermediate in size and not visibly suspended
|Particles settle at the bottom of the container due to gravity
|Particles do not settle due to their intermediate size
|Mixture appears cloudy or turbid
|Mixture appears homogeneous
|Properties can vary depending on location within the mixture
|Properties are uniform throughout the mixture
|Filtering can separate particles from the liquid or gas
|Particles cannot be separated by filtering