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## Chapter 1: Some Basic Concepts of Chemistry ### Give two differences between: Mixtures and pure substances * **Mixtures:** * Mixtures have no definite chemical composition. * Mixtures have no definite properties. * **Pure substances:** * Pure substances have a definite chemical com...
## Chapter 1: Some Basic Concepts of Chemistry ### Give two differences between: Mixtures and pure substances * **Mixtures:** * Mixtures have no definite chemical composition. * Mixtures have no definite properties. * **Pure substances:** * Pure substances have a definite chemical composition. * Pure substances always have the same properties regardless of their origin. **e.g.** * **Paint** (mixture of oils, pigment, additive), **concrete** (a mixture of sand, cement, water), etc. * **Pure metal**, **distilled water**, etc. ### Explain: States of matter * **Solid:** Particles are held tightly in perfect order. They have definite shape and volume. * **Liquid:** Particles are close to each other but can move around within the liquid. * **Gas:** Particles are far apart as compared to that of solid and liquid. These three states of matter can be interconverted by changing the conditions of temperature and pressure. ### Properties of matter and their measurement * **Physical properties:** These are properties which can be measured or observed without changing the identity or the composition of the substance. * **e.g.** Colour, odour, melting point, boiling point, density, etc. * **Chemical properties:** These are properties in which substances undergo change in chemical composition. * **e.g.** Coal burns in air to produce carbon dioxide, magnesium wire burns in air in the presence of oxygen to form magnesium oxide, etc. ### How are properties of matter measured? Measurement involves comparing a property of matter with some fixed standard which is reproducible and unchanging. Properties such as mass, length, area, volume, time, etc. are quantitative in nature and can be measured. A quantitative measurement is represented by a number followed by units in which it is measured. These units are arbitrarily chosen on the basis of universally accepted standards. * **e.g.** Length of classroom can be expressed as 10 m. Here, 10 is the number and 'm' is the unit 'metre' in which the length is measured. ### Define: Units The arbitrarily decided and universally accepted standards are called units. * **e.g.** Metre (m), kilogram (kg). ### What are the various systems in which units are expressed? Units are expressed in various systems like CGS (centimetre for length, gram for mass and second for time), FPS (foot, pound, second) and MKS (metre, kilogram, second) systems, etc. ### What are SI units? Name the fundamental SI units. **SI Units:** In 1960, the general conference of weights and measures proposed revised metric system, called International system of Units i.e. SI system (abbreviated from its French name). The seven fundamental SI units are as given below: | No. | Base physical quantity | SI unit | Symbol | |---|---|---|---| | i. | Length | Metre | m | | ii. | Mass | Kilogram | kg | | iii. | Time | Second | s | | iv. | Temperature | Kelvin | K | | v. | Amount of substance | Mole | mol | | vi. | Electric current | Ampere | A | | vii. | Luminous intensity | Candela | cd | **Note:** Units for other quantities such as speed, volume, density, etc. can be derived from fundamental SI units.
