Give the distinguishing features of a pure substance or a compound and a mixture.
Various points of distinction between a chemical compound and a mixture are summarised below:
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Characteristics |
Pure substance or compound |
Mixture |
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1. Composition
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The elements in a compound are present in definite proportion by weight.
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The ingredients of a mixture may be present in varying ratio. |
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2. Homogeneity
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A compound is always homogeneous.
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A mixture may be homogeneous (solution) or heterogeneous. The constituents of a mixture can be separated by simple methods.
|
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3. Properties |
.A compound has entirely different properties from those of its constituents.
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Properties of a mixture are an average of the properties of its constituents.
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4. Separation
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The constituents of a compound cannot be separated by simple separation techniques |
The constituents of a heterogeneous mixture can be separated by simple physical separation techniques. |
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5. Energy changes
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Energy in the form of heat, light or electricity is either evolved or absorbed when a compound is formed. |
There is generally no energy change when a mixture is formed from its constituents. |
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6. Volume change |
At constant temperature and pressure, formation of a compound may involve either no change or large change in volume. |
At constant temperature and pressure, formation of a mixture involves either very little or no change in volume. |
How do you establish that air is a mixture and not a pure substance?
List the various types of homogeneous and heterogeneous mixtures with examples.
How will you prepare a saturated solution of copper sulphate in water at 50°C? What will happen if this solution is allowed to cool?
How do you express concentration of a solution?
