Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.
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Sublimation
Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase. Examples is ammonium chloride when heated changes from solid to gas.Even camphor and dry ice undergo sublimation.
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Boiling point and normal boiling point
The boiling point of a substance is the temperature at which the vapour pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapour at STP.The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the special case in which the vapour pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere.
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Factors affecting boiling point
Pressure: If the external pressure is higher than one atmosphere, the liquid will boil at a higher temperature than the normal boiling point.
Molecule Types: Types of molecules in the liquid affect the boiling point of the liquid. If the force of attraction between the molecules is relatively strong, the boiling point will be relatively high. If the force of attraction between molecules is relatively weak, the boiling point will be relatively low.
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Boiling point and melting point of different substances
The boiling point is the temperature at which a material changes from a liquid to a gas (boils). Here are boiling point of different substances: pentane (360C), Bromine (58.50C), Water (1000C etc. The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. Here are melting point of different substances: mercury (38.830C), water (00C) Aluminum (6000C) etc.
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Experimentally define melting point of ice
Here is the procedure to determine the melting point of ice: 1. Take some ice cubes and dry them using a filter paper and quickly put them in a beaker. 2. Place the beaker over a wire gauze kept over a tripod stand. 3. Suspend a thermometer (temperature range -10 to 110C) with the help of a clamp stand so that its bulb remains in the middle of the ice cubes. 4. Ice cubes are moderately heated by a gas burner and stirred continuously using a glass rod. 5. Note the temperature (t1) when the ice starts melting.Continue heating the ice. 6. Note the temperature (t2) when the ice has melted completely. 7. Record your observations in tabular form t1 in one column and t2 in another column.Now find the average of t1 and t2 which will give you the melting point of ice.
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Experimentally define boiling point of water
Here is the procedure for finding the boiling point of water : 1. Take about 25ml of distilled water in a boiling tube and add 2−3 small pieces of pumice stone. 2. Close the mouth of the boiling tube with a rubber cork that has two bores and clamp it with the stand. 3. Introduce a thermometer (temperature range −10to110C) in one bore of the cork of the boiling tube. Keep the bulb of the thermometer about 3−5cm above the surface of the water. 4. Then introduce one end of a delivery tube in the second bore of the cork.Place a 250ml beaker below the second end of the delivery tube to collect the condensed water. 5. Heat the boiling tube gently, preferably by rotating the flame. 6. Note the temperature (t1) when the water starts boiling. 7. Continue to heat the water till the temperature becomes constant, and the water remains boiling. Note the constant temperature (t2). 8. Record your observations in tabular form t1 in one column and t2 in another column.Now find the average of t1 and t2 which will give you the boiling point of water.