Category Chemistry

When does litmus paper turn Red?

Litmus paper turns red when placed in an acid solution, but blue is the solution is alkaline. This absorbent paper is the oldest and most commonly used indicator of the presence or absence of acid. Its special qualities are due to the fact that it has been soaked and impregnated with a mixture of dyes called litmus.

        The litmus mixture was originally produced by the action of air, ammonia and an alkali carbonate on certain lichens found in the Netherlands. It is now made from azolitmin and erythrolitmin.

     A litmus solution is sometimes used. But the message is the same. A few drops added to a liquid turn it red if it is acid and blue if it is alkaline.

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What is a detergent?

A detergent is substances which has a power to cleanse. This description applies to soap, as well as to soap, as well as to soapless shampoos and washing powders. A detergent usually has surface activating properties, which means that it is able to reduce the surface tension of water.

      In the process of cleaning the detergent acts as a bridge between the solid matter and the water. Soap molecules are shaped like tadpoles. The head is soluble, but the rod-like body is composed of an insoluble fatty substance. When mixed with water part of the soap tries to get away and the rest stays, thus breaking down the water’s surface tension. There is not sufficient room for all the soap molecules on the surface of the water. So they form bundles with the water-resisting rods on the inside. The dirt attracts the fatty part of the soap molecules which lift and surround it, while the soluble part of the molecules lifts and rinses the dirt away.

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Where does the wax go when a candle burns?

Nowhere- it simply changes into other substances. That is what burning does to everything.

       The moment you put a match to the wick, you start a change in the candle by turning the solid wax into a liquid. The liquid wax rises to the wick by an irresistible process called capillarity, the simplest example of which is the way blotting paper soaks up ink or water. Then the liquid wax changes into a gas which burns-a chemical reaction which releases energy in the form of light and heat.

     The presence of the gas can be demonstrated by blowing out the candle and immediately holding a lighted match an inch or so above the wick. The inflammable vapour instantly catches fire and the candle lights up again without the match having actually touched the wick.

     Other changes are taking place while the candle burns. The wax is a complex chemical compound of carbon and hydrogen. The process of burning is simply the combination of the wax with the oxygen in the air. If you put a jar over the candle, it will quickly use up the oxygen and go out.

Suring the time the candle burns, the carbon joins with the oxygen in the air and makes carbon monoxide and carbon dioxide, and the hydrogen combines with the oxygen to produce water.

    While all these changes in the substance of the candle are taking place, the candle, of course, is becoming shorter. But it is not “going” anywhere. Its materials are simply changing into other substances.

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Why do some liquids burn?

Some liquids will burn because when their molecules mix with the oxygen in the air the mixture becomes combustible.

       The application of heat promotes the necessary chemical re-action to put the molecules into more violent motion, so that they collide at high speed. The jolt loosens the bonds and makes it easier for the molecules to rearrange themselves and escape from the liquid to form a vapour, mixing with oxygen in the air.

       The most important liquid which will burn is crude mineral oil from which petrol and paraffin are produced. Others include tar and creosote, and the very explosive nitro-glycerin.

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Why is pollution a problem?

Pollution is a problem because man, in an increasingly populated and industrialized world, is upsetting the environment in which he lives. Many scientists maintain that one of man’s greatest errors has been to equate growth with advancement. Now “growth” industries are being looked on with suspicion in case their side effects damage the environment and disrupt the relationship of different forms of life.

       The growing population makes increasing demands on the world’s fixed supply of air, water and land. This rise in population is accompanied by the desire of more and more people for a better standard of living. Thus still greater demands for electricity, water and good result in an ever increasing amount of waste material to be disposed of.

    The problem has been causing increasing concern to living things and their environment. Many believe that man is not solving these problems quickly enough and that his selfish pursuit of possessions takes him past the point of no return before he fully appreciates the damage. It would then be too late to reverse the process.

    Ecologists say we are so determined to possess a new car or washing machine, or to obtain a greater yield from our crops by the use of fertilizers, that we ignore the fact that life depends on a lot of micro-organisms working efficiently.

     For example, if new chemicals were released into the environment, a combination of them might well poison one or more of the different type of bacteria in soil and water, which are essential to keep nitrogen being circulated from the air into organic material, and being cycled back into the air again. If this should happen on a world-wide scale, the air would become unbreathable.

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How do fire extinguishers work?

Fire extinguishers stop flames either by dousing them in water or by dousing them in water or by excluding the oxygen which a fire needs in order to burn.

     There are three main kinds of fires. First are those occurring in ordinary materials like paper and wood for which the quenching and cooling effects of water or water solutions are the most effective. Second come those involving inflammable liquids or greases for which a blanketing or smothering effect is essential. Finally there are the fires occurring in “live” electrical equipments where a special extinguishing agent must be used.

     The most common extinguisher for the first type of fire is a bucket of water, or a manufactured extinguisher with water containing a chemical. The chemical reaction expels the water which puts out the fire.

    For the second kind of fire the most common method is to use a chemical extinguisher to blanket the burning material, excluding oxygen and thus putting out the fire. When oil or grease is burning you should not use a foam-type extinguisher, as it may contain a certain amount of water. However these foam-type extinguishers are safe in most other cases, except electrical fires.

     For oil, grease or electrical fires a powder extinguisher must be used, never water or foam, as these could conduct electrical current.

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