Revision: Is Matter Around Us Pure Science English Medium Class 9 CBSE

Chemical properties of matter tell us how a substance changes when it interacts with other substances. These properties describe how matter reacts and forms new substances. When a chemical change happens, the matter changes into something new. The atoms in a substance rearrange themselves, and a new substance is formed. For example:

• When wood burns, it turns into ash and smoke.
• When iron is exposed to air and water, it forms rust.

Examples of Chemical Properties:

• Flammability: This describes if a substance can burn. For example, wood is flammable because it can catch fire.
• Reactivity: This tells us how a substance reacts when mixed with others. For example, if you mix vinegar with baking soda, they react to create bubbles.
• Rusting: Some metals, like iron, will form rust when they come in contact with water and air.
• Acidity and Basicity: Some substances are acidic (like lemon juice), while others are basic (like soap). Acids and bases can react with each other to form new substances.

• Matter is defined based on its physical and chemical structure. It occupies space and has mass, particularly as opposed to energy.
• Atoms and molecules are the building blocks of matter, consisting of positively charged protons, neutral neutrons, and negatively charged electrons, respectively.

The matter is defined as anything that has mass and takes up space. The matter is found in solid, liquid and gas.

Atom — An atom is the smallest part of an element that takes place in a chemical reaction.

Matter—Anything that has mass and occupies space is called matter.

Anything that has mass and occupies space is called matter.

An emulsion is a colloid in which minute droplets of one liquid are dispersed in another liquid which is not miscible with it. Examples are milk and butter.

Homogeneous mixture: “A mixture in which its constituents are uniformly distributed throughout its volume and cannot be seen separately is called a homogenous mixture.”

Mixtures are formed when two or more substances are mixed together without participating in a chemical change. A mixture has a variable composition. A mixture shows the properties of the constituent substances. Physical methods can easily separate the constituents.

• Atoms/molecules of a mixture are of two or more types.
• The constituent molecules of a mixture are different from each other and are not joined by chemical bonds.
• Components in a mixture retain their original properties because they are not chemically combined.
• The proportion of constituent substances in a mixture can change.
• The properties of constituent substances are retained in the mixture. 
• Unlike compounds, mixtures do not have a fixed ratio of their components.

For Examples,

Air is a mixture containing nitrogen (N₂), oxygen (O₂), and other gases.

Types of mixture

1. Homogeneous Mixtures: Homo means same. A homogeneous mixture is a mixture in which the composition is uniform throughout the mixture. For example, salt in water. It has a uniform composition, and it can’t be separated out physically.
2. Heterogeneous Mixture: Hetero means different. A heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture. For example, vegetable soup. It has a non-uniform composition and can be separated out physically.

Miscible liquids : Homogeneous liquid-liquid mixtures are called miscible liquids.

Immiscible liquids : Heterogeneous liquid-liquid mixtures are called immiscible liquids.

Pure substance: “Pure Substance is either element or compound. It contains the same kind of atom or molecules and has a definite set of physical and chemical properties.”

Impure substance: “A substance in which some other substances are also present in smaller or larger amounts is called an impure substance. Mixtures are impure substances. An example of an impure substance is air.

Solution: “The homogeneous mixture of water (or any other solvent) and a substance soluble in it is called a solution.”

Heterogeneous mixture: “A mixture in which the components are not uniformly distributed through its volume and can be easily seen separately is called a heterogeneous mixture.”

Alloy: “A homogeneous solid mixture of two or more metals or a metal and a non-metal is called an alloy.”

A homogeneous mixture of two or more substances, whose relative amounts may be changed within certain limits, is called a solution.

• Unsaturated solution: If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution. (till it is dissolving).

• Saturated solution: When no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

• Solubility: The amount of the solute present in the saturated solution at this temperature is called its solubility.

Suspension: A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.

• Colloids: A colloid is a type of mixture where tiny particles of one substance are dispersed evenly throughout another substance. These particles are small but still larger than molecules or simple ions.
• Dispersed Phase: The phase that is dispersed or present in the colloidal particle shape is called the dispersed phase. 
• Dispersion medium: Dispersion medium is the continuous phase of a colloid. It is the phase in which the dispersed phase is distributed.

Evaporation: Evaporation is a process which is used to separate a solid substance dissolved in liquid. It is based on the fact that liquids vaporize easily whereas solids do not.

Evaporation Is the process of converting a liquid into its vapour state either by exposing it to air or by heating.

Evaporation : Is the process ~of converting a liquid into its vapours state either by exposing it to air or by heating.

The change of a solid substance directly into a gas or vapour without first changing into a liquid is called sublimation.

OR

The change from solid state to vapour state without passing through the liquid state is called sublimation, and the substance is said to sublime.

The change of state from solid to gas directly is called sublimation.

Stationary phase is a solid or a liquid supported on a solid which remains fixed in a place and on which different solutes are adsorbed to a different extent.

Distillation : Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.

The process in which liquid is converted into its vapor phase at its boiling point and the vapor is then condensed back to liquid on cooling is known as distillation.

A permanent change in which new substances are formed whose composition and properties are completely different from those of the original 
substances.

Chemical change:
(i) Burning of wood.
(ii) Breathing.

Physical change: A temporary change in which no new substance is formed, the composition of substance remains the same, though its state, shape and size may change.

Example of physical change:

1. Change of water into its vapours.
2. Heating of iron rod.

A chemical change is a permanent change in which the chemical composition of a substance is changed and one or more new substances with different chemical compositions and different properties are formed.

A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.

Any chemical change in matter that involves its transformation into one or more new substances is called a chemical reaction.

An electrochemical reaction is a chemical reaction involving the transfer of electrons, where oxidation and reduction occur simultaneously.

Chemical reactions which are characterised by the formation of insoluble solid substances are called precipitates.

A chemical reaction in which two compounds in their aqueous state react to form an insoluble salt as one of the products.

The cell which converts electrical energy into chemical energy is called an electrolytic cell and the process which converts electrical energy into chemical energy is called electrolysis.

The substances formed as a result of a chemical reaction by formation of new bonds are called products.

A chemical change is a process in which the composition of matter changes, resulting in the formation of one or more new substances.

The substances taking part in chemical reaction are called reactants.

A chemical reaction that occurs in the presence of light is called a photochemical reaction.

Compounds: Compounds are pure substances composed of two or more elements in definite proportion by mass and has a definite set of properties. The compound is made up of only one kind of molecules

Molecule: A molecule can be defined as the smallest unit of an element or a compound which exhibits all the properties of that element or compound and has an independent existence. They are divisible into atoms.

Element is a substance which cannot be split up into two or more simple substances by usual chemical methods of applying heat, light or electric energy; for example, hydrogen, oxygen and chlorine.

Atom: An atom is the smallest indivisible unit of an element which exhibits all the properties of that element and may or may not have an independent existence. An atom is the smallest indivisible unit of an element which exhibits all the properties of that element and may or may not have an independent existence. 

Formula: Formula is a short way of representing the molecule of an element or a compound

Element is a substance which cannot be broken further into simpler substances and has a definite set of properties. Elements are made up of only one kind of atoms.

Elements: An element is defined as a pure substance made up of only one kind of atoms that cannot be converted into anything simpler than itself by any physical or chemical process. 

“Mixtures can be defined as. a kind of matter which is formed by mixing two or more pure substances (elements and compounds) in any proportion, such that they do not undergo any chemical change and retain their individual properties. Therefore they are impure substances.

The number of atoms in a molecule of an element is called its atomicity. 

Compounds are pure substances composed of two or more elements in definite proportion by mass and has properties, entirely different from those of its constituents elements.
Compound, are made up of different types of atoms combined chemically.