| Mixtures | Compounds |
|---|---|
| 1.A mixture can be separated into its constituents by the physical Though a compound is always homogeneous, So,being homogeneous or heterogeneous is usually not helpful in deciding whether a substance is a mixture or a compound and, therefore, this point has not been included in the above table. In order to find out whether a given substance is a mixture or compound, we should remember that: 1.(i) If the substance can be separated into its constituents by physical methods, it is a mixture. (ii) If the substance cannot be separated into its constituents by physical methods, it is a compound. 2.(i) If the substance shows the properties of its constituents, it is a mixture. (ii) If the properties of the substance are entirely different from those of its constituents, it is a compound. 3.(i) If no heat or light, etc.,is given out or absorbed during the preparation of the substance,it is a mixture. (ii) If heat or light, etc., is given out or absorbed during the preparation of the substance, it is a compound. 4.(i) If the composition of the substance is variable, it is a mixture. (ii) If the composition of the substance is fixed, it is a compound. 5.(i) If the substance does not have a fixed melting point, boiling point, etc.,it is a mixture. (ii) If the substance has a fixed melting point, boiling point, etc., it is a compound. Keeping these five points in mind, we will now answer some important questions on mixtures and compounds. Sample Problem 1. Explain why, air is considered a mixture and not a compound. Solution. Air is considered a mixture because of the following reasons : (i)Air can be separated into its constituents like oxygen, nitrogen, etc.,by the physical process of fractional distillation (of liquid air). (ii) Air shows the properties of all the gases present in it. For example, oxygen supports combustion and air also supports combustion; carbon dioxide turns lime water milky and air also turns lime water milky, though very, very slowly. (iii) Heat and light, etc., are neither given out nor absorbed when air is prepared by mixing the required proportions of oxygen, nitrogen, carbon dioxide, argon, water vapour, etc. (iv) Air has a variable composition because air at different places contains different amounts of the various gases. It does not have a definite formula. (v) Liquid air does not have a fixed boiling point. Sample Problem 2. Explain why, water is a compound and not a mixture. Solution. Water is considered a compound because of the following reasons : (i) Water cannot be separated into its constituents, hydrogen and oxygen, by the physical methods (such as filtration, evaporation, distillation, sublimation, magnet, etc.). (ii) The properties of water are entirely different from those of its constituents, hydrogen and oxygen.For example, water is a liquid whereas hydrogen and oxygen are gases; water does not bum whereas hydrogen bums; water does not support combustion whereas oxygen supports combustion. (iii) Heat and light are given out when water is prepared by burning hydrogen in oxygen. (iv) The composition of water is fixed. It contains hydrogen and oxygen combined together in a fixed proportion of 1 : 8 by mass. It has a definite formula,. (v) Water has a fixed boiling point of 100°C under standard atmospheric pressure. Sample Problem 3.Classify the following into elements, compounds and mixtures : Sodium, Soil, Sugar solution, Silver, Calcium carbonate, Tin, Silicon, Coal, Air,Soap, Methane, Carbon dioxide, Blood Solution. We can classify the given materials into elements, compounds and mixtures as follows : Elements Compounds Mixtures Sodium Calcium carbonate Soil Silver Soap Sugar solution Tin Methane Coal Silicon Carbon dioxide Air Blood Sample Problem 4. Give the names of the elements present in the following compounds : (a) Quicklime (b) Hydrogen bromide (c) Baking soda (d) Potassium sulphate Solution, (a) Quicklime is calcium oxide,.The elements present in it are: Calcium () and Oxygen (O). (b) Hydrogen bromide is HBr. The elements present in it are : Hydrogen (H) and Bromine (Br). (c) Baking soda is sodium hydrogencarbonate,.The elements present in it are : Sodium (Na),Hydrogen (H), Carbon (C) and Oxygen (O). (d) Potassium sulphate is .The elements present in it are: Potassium (K), Sulphur (S) and Oxygen(O).evaporation,sublimation, distillation, solvents, magnet, etc.). 2.A mixture shows the properties of its constituents. 3.Energy (in the form of heat, light, etc.) is usually neither given out nor absorbed in the preparation of a mixture. 4.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. 5.A mixture does not have a fixed melting point, boiling point, etc. | 1.A compound cannot be separated into its constituents by physical processes (It can only be separated into its constituents by chemical processes). 2.The properties of a compound are entirely different from those of its constituents. 3.Energy (in the form of heat, light, etc.) is usually given out or absorbed during the preparation of a compound. 4.The composition of a compound is fixed, the constituents are present in fixed proportion by mass.A compound has a definite formula. 5.A compound has a fixed melting point, boiling point,etc. |
