# Is Matter Around us Pure?

Tutormate > CBSE Syllabus-Class 9th Chemistry > Is Matter Around us Pure?

## 9 Compounds

• A compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass.
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Properties of a Compound:

• A compound cannot be separated into its components by physical methods.
• The properties of a compound are entirely different from those of its constituent elements.
• Energy in the form of heat, light, etc. is usually either given out or absorbed during the preparation of a compound.
• The composition of compound is fixed, the constituents are present in a fixed proportion by mass.
• Compound is a homogeneous substance.

Chemical Formula:

• Compounds are represented by their chemical formula which gives information about the proportions of atoms that constitute a particular chemical compound.
• The chemical formula of water iswhich shows two atoms of hydrogen and one atom of oxygen have combined to form one molecule of.
• The chemical formula for common salt iswhich shows one atom of sodium and one atom of chlorine combine to form one molecule of.

Examples of some commonly used compounds and their molecular formula:

 Name of the compound Formula of the compound Alcohol ${\mathrm{C}}_{2}{\mathrm{H}}_{6}\mathrm{O}$ Acetic Acid ${\mathrm{C}}_{2}{\mathrm{H}}_{4}{\mathrm{O}}_{2}$ Sulphuric Acid ${\mathrm{H}}_{2}{\mathrm{SO}}_{4}$ Ammonia ${\mathrm{NH}}_{3}$ Methane ${\mathrm{CH}}_{4}$ Nitrous oxide ${\mathrm{N}}_{2}\mathrm{O}$ Salt $\mathrm{NaCl}$

Differences Between Mixtures and Compounds:

 Mixture Compounds A mixture can be separated into its constituents by the physical processes like filtration, evaporation, sublimation, distillation, solvents magnet, etc. A compound can be separated into its constituents by chemical processes. A mixture shows the properties of its constituents. The properties of a compound are entirely different from those of its constituents. Energy in the form of heat, light, etc. is usually neither given out nor absorbed in the preparation of a mixture. Energy in the form of heat, light, etc. is usually given out or absorbed during the preparation of a compound. The composition of a mixture is variable, the constituents can be present in any proportion by mass. A mixture does not have a definite formula. The composition of a compound is fixed, the constituents are present in fixed proportion by mass. A compound has definite formula. A mixture does not have a fixed melting point, boiling point, etc. A compound has a fixed melting point, boiling point, etc.

Alloys

An alloy is considered a mixture because:

• it shows the properties of its constituents
• it has a variable composition

Brass is considered a mixture because:

• it shows the properties of its constituents, copper and zinc
• it has a variable composition