Pure Substances
- Pure substances, like elements or compounds such as diamond or carbon dioxide, consist of a single type of entity and cannot be broken down further through chemical or physical methods.
- Elements, in particular, are pure materials made up of only one type of atom, ensuring consistency in composition and properties.
- These substances exhibit homogeneity, with constant boiling and melting points.
- In chemical reactions, pure substances play a role, producing predictable outcomes due to their stable nature.
Mixtures
It is made up of two or more elements or compounds mixed in any ratio/proportion.
Properties
- It may be homogeneous or heterogeneous.
- The properties of constituent substances are retained.
- No new compound is formed after mixing.
- Constituents of a mixture can be separated by simple physical processes.
- It does not have a fixed melting and boiling point.
Question for Short Notes: Is Matter Around Us Pure
Try yourself:Mixture can be
Explanation
Mixtures can be either homogeneous or heterogeneous: a mixture in which constituents are distributed uniformly is called homogeneous, such as salt in water, otherwise, it is called heterogeneous, such as sand in water.
So, Option C i.e Both (a) and (b) is correct.
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Solution
A solution is a homogeneous mixture of two or more substances (e.g., Lemonade, soda water).
Table: Difference between Solute and Solvent.
Concentration of Solution
- The amount of solute that has dissolved in a specific amount of solvent or solution is measured as solution concentration.
- A concentrated solution is one that has a significant amount of dissolved solute in it.
- A diluted solution is one that has a small amount of dissolved solute in it.
Alloys
Alloys are homogeneous mixtures of metals or a mixture of a metal and another element that cannot be separated into their components by physical methods.
Examples:
- Steel – a combination of iron (metal) and carbon (non-metal).
- Bronze – a combination of copper (metal) and tin (metal).
- Brass – a mixture of copper (metal) and zinc (metal).
Suspension
A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Ex: Chalk in water, smoke in the air
Properties of Suspension :
- It is a heterogeneous mixture.
- Particles of a suspension are visible to the naked eye.
- The size of the particles is greater than 100 nm.
- It is an unstable mixture. Solute settles down at the bottom over the period.
- If the solution is passed through filter paper, the solute and solvent get separated.
- It scatters light when light is passed through the solution i.e. it shows the Tyndall effect.
Colloidal Solution
A colloid solution is a heterogeneous mixture in which the size of particles lies between the true solutions and suspensions. - Colloidal particles can easily scatter a beam of visible light.
- This phenomenon is called the Tyndall effect.
Properties of Colloidal Solution:
- The particles of colloids can’t be seen by the naked eye individually.
- It is a heterogeneous mixture and thus solute and solvent can’t be separated by filter paper.
- The size of particles is smaller than suspensions but greater than solutions (1 nm to 100 nm).
- It is a stable mixture. Particles do not settle down at the bottom over a period of time.
- They do not settle down when left undisturbed which means colloid is quite stable.
Question for Short Notes: Is Matter Around Us Pure
Try yourself:In sugar solution,
Explanation
A solute is a substance that is "dissolved into" the solvent, while the solvent is the substance "into which" something is dissolved. Now, when we prepare sugar water, we mix sugar into water and thus sugar is the solute, while water is the solvent.
So, Option A is correct.
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Physical and Chemical Change
Types of Pure Substances
The pure substance is divided in two types based on their chemical composition:
(i) Elements
- According to Antoine Laurent Lavoisier, the element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
- It is divided into three types which are metals, non-metals and metalloids.
Properties of MetalsThey have a lustre (shine).
They have a silvery-grey or golden-yellow colour.
They conduct heat and electricity.
They are ductile (can be drawn into wires).
They are malleable (can be hammered into thin sheets).
They are sonorous (make a ringing sound when hit).
Examples: gold, silver, copper, iron, sodium, potassium etc. are Metals
Note: Mercury is the only metal that is liquid at room temperature.
Properties of non-metalsThey display a variety of colours.
They are poor conductors of heat and electricity.
They are not lustrous, sonorous or malleable.
Examples of non-metals are hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc.
Metalloids: Elements having intermediate properties between those of metals and non-metals are called metalloids. Examples are boron, silicon, germanium etc.
Question for Short Notes: Is Matter Around Us Pure
Try yourself:
What is a solution?Explanation
- A solution is a homogeneous mixture of two or more substances.
- It is made up of a solute (the substance being dissolved) and a solvent (the substance in which the solute is dissolved).
- In a solution, the solute particles are evenly distributed throughout the solvent, resulting in a uniform composition.
- Examples of solutions include lemonade and soda water.
- Solutions can be separated by physical processes such as filtration or evaporation.
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(ii) Compounds
A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.
Characteristics
- The properties of a compound differ from those of its constituents.
- The compound has a fixed melting point and boiling point.
- A compound is a homogeneous substance.
- Constituent elements can be separated by chemical processes.