Is Matter Around us Pure?

• A compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass.
• $\mathrm{Water} \left({\mathrm{H}}_2\mathrm{O}\right) \mathrm{is} \mathrm{a} \mathrm{compound} \mathrm{made} \mathrm{up} \mathrm{of} \mathrm{two} \mathrm{elements}, \mathrm{hydrogen} \mathrm{and} \mathrm{oxygen} \mathrm{chemically} \mathrm{combined} \mathrm{in} \mathrm{a} \mathrm{fixed} \mathrm{proportion} \mathrm{of} \mathrm{by} \mathrm{mass}.$

   

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.

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