Which gas is emitted when a matchstick is lit?

Which gas is emitted when a matchstick is lit?

The type of gas that is emitted when a matchstick is lit depends on the material used in the matchstick heads. The usually used match stick heads are an admixture of red sulphur in major portion and red phosphorous in trace quantities.When the matchstick is struck on the box, the friction caused is sufficient to ignite the phosphorus. The combustion of phosphorus is exothermic and hence releases heat. The sulphur in the head in turn catches fire by reacting with atmospheric oxygen to give sulphur dioxide. The gas that is emitted, when an ordinary matchstick is lit, is, therefore, sulphur dioxide. The cellulose of the matchstick that is subsequently burnt emits CO{-2}gas. . In matchsticks, such as those used in Diwali fireworks, a variety of chemicals, in minimal quantities, are used for a variety of colours and a sparkling effect.

Source: thehindu.com

What are the differences between an ordinary soap and detergent in composition and action?

What are the differences between an ordinary soap and detergent in composition and action?

Soaps are sodium or potassium salts of long chain carboxylic acids (fatty acids) whereas detergents are salts of long chain sulphates or sulphonates. Hence, soaps and detergents have a long organic tail with a (negatively charged) polar head, that is, they are anionic in nature. The organic tail is hydrophobic (water-hating) but lyophilic (oil-loving) whereas the polar head is hydrophilic (water-loving) and lyophobic (oil-hating).The cleansing action of both detergents and soaps is about the same.

Dirty clothes and skin have oily layers. Simple wetting and rinsing of such clothes and skin would not remove the dirt because the oil is immiscible in water. When a detergent or soap is used along with water, the lyophilic tails of the detergent species tag on to the oily layer while the hydrophilic heads face the water. The agitation causes the oily matter to break into small droplets and is trapped inside the lyophilic `cage' formed by the detergent molecules. Thus the oily matter is kept suspended in water. The structure formed by the detergent molecules where the oil is trapped is called a micelle. The role of the detergent molecules is to prevent the oil droplets from coalescing once again and returning to the cloth. The differences between soaps and detergents stem from their sensitivities to hard water and acidic conditions. When hard water (which contains magnesium and calcium ions in more than permitted levels) is used, the soap precipitates out as calcium or magnesium salts. On the other hand, the detergents are less prone to complexation with the metal ion and hence would be less affected by the hard water. Likewise, the soap would precipitate out under acid conditions as the carboxylic acid group would be protonated, while the detergent would survive acidic conditions better.

Source: thehindu.com

Why does magnesium react mildly with cold water but vigorously with hot water or steam producing magnesium hydroxide and hydrogen?

Why does magnesium react mildly with cold water but vigorously with hot water or steam producing magnesium hydroxide and hydrogen?

Magnesium, being an alkaline earth rare earth (s-block) metal, reacts with water more actively than most other transition (d-block) metals such as iron, copper, zinc, etc do. Yet the reaction is slower compared with the alkali metals such as lithium, sodium and potassium, which react violently with, even ice-cold water. 

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Magnesium reacts with water to give magnesium hydroxide and hydrogen as follows:Mg+2H{-2}O -> Mg(OH){-2}+H{-2}Normally Mg is coated with a thin layer of its oxide (MgO) when it is exposed to air. This layer induces passivity to Mg in its reaction with water.The rate of any reaction depends on the kinetic energy of the reactants (chemicals participating in the reaction). In other words, the reactants can transform chemically only when they possess a minimum kinetic energy known as `activation energy.' According to the Boltzmann distribution of energies, and the Arrhenius theory of reaction rates, the number of entities possessing activation energy and hence the reaction rate increase with increasing temperature. Therefore, we can say that the above reaction happens more speedily with hot water and steam. In cold water neither the activation energy is supplied nor the oxide layer is disturbed to promote further reaction of magnesium.The rate of any chemical reaction is also accentuated by factors that destabilise the reactants and those that remove the products from the scene of the reaction or stabilise the products.

The hydrogen atoms produced, are initially adsorbed on the surface of magnesium metal before they leave as hydrogen molecules. Thus, the metal surface is dynamically dressed by hydrogen atoms and thereby screened from further attack by water.Hence, the reaction is mild in cold water. When the magnesium metal is exposed to hot water or steam, the temperature of the metal increases and its interatomic bonds loosen (destabilise) making the magnesium atoms to give away their electrons more readily.Besides, the hydrogen atoms produced, are not effectively adsorbed on the hot surface of the magnesium metal and the metal is, thereby, continuously exposed to the attack of hot water molecules. Further, in hot water, the water molecules are more ionised (destabilised) giving more number of hydrogen ions to accept the electrons and more hydroxide ions to form the stable magnesium hydroxide. Hence, the reaction is vigorous in hot water and in steam.Another equally important reason for the vigorous reaction in hot water is that the produced hydrogen gas is more thoroughly expelled from the layer of magnesium than in cold water due to the prevailing turbulence and also as gases are generally less soluble under hot conditions in liquids.

Source: thehindu.com