My Science School

    A phenomenon called polarity prevents oil and water from mixing. All molecules carry electrical charge which is distributed uniformly or non-uniformly over the length of the molecule. In polar compounds, the positive and negative charges are concentrated at the two ends of the molecule. When such substances are mixed together, the positive and negative regions of their molecules attract each other and as a result a clear solution is obtained. Water is a polar substance and mixes freely with other polar substances. Oil molecules, on the other hand, are non-polar. When polar and non-polar substances are mixed together, the mutual attraction of polar molecules separates out the non-polar molecules and the two substances do not mix.   

     The solubility of a substance depends on the nature of bonding in both the solute and the solvent. Salt is an ionic substance; that is, its atoms are held together by opposite electrical charges. Water molecule also has electrical charges – the hydrogen atoms are positively charged and the oxygen atom negatively charged. When salt is put in water the charges on the water molecule pull the oppositely charged atoms in salt apart, thus dissolving it. Oil molecules, on the other hand, do not carry any charge and so does not have any effect on the ionic bonds in salt when put in it. As a result, salt does not dissolve in oil.

                                    

            A knot in a lace is held together by the friction between the surfaces of the lace. Greater the friction more stable the knot will be. Since there is enough friction between cotton fibres in a lace made of cotton, it is quite easy to tie a knot. But silk being a smooth fibre, a knot tied with a silk lace becomes loose and opens up easily due to lack of friction between the fibres.

                                    

   Bubbles are balls of thin soap films. They show rainbow colours because the light falling on them undergoes what is known as interference. Light travels in the form of waves which have troughs and peaks at regular intervals. For instance, one wavelength of a light-wave has one trough and one peak. When light falls on a soap bubble it is reflected from both the upper and lower surfaces of the film. Thus, there are two waves of reflected light emerging out of surfaces of the soap bubble. If the distance between the two surfaces of the film is less than one wavelength of light, the two reflected waves are so close that interference occurs. The peaks of the two waves may add up and become a bigger peak. Or the trough of one wave may fall with the peak of the other thus cancelling its effect. As the seven component colours of white light have different wavelengths, the adding or cancelling effect of interference is not the same on all of them. In other words, some colours become brighter and some duller. Thus a viewer sees a mixture of rainbow colours instead of the white light emerge from the soap bubble.

                                    

Foam or lather is nothing but a large collection of small soap bubbles. A soap bubble is, in turn, a very thin film of soap solution enclosing some in air. Because of the low surface tension of soap solution, the film can stretch and spread and form innumerable bubbles with a very large total surface area. Because of this, whatever slight tint present in the thin film of the coloured soap solution gets subdued. Although a soap film is more or less transparent, the lather or foam looks white because the light striking this large collection of bubbles gets scattered. That is why all kinds of foam look white.

                                    

  One of the laws of fusion is that the melting point of substances which expand on freezing is lowered by the increase of pressure, while it is raised in the case of those which contract on solidification. Ice belongs to the first category of substances, that is, it expands on freezing. Ice has an open structure which collapses when subjected to pressure, producing water which occupies lesser volume. That is why ice melts when subjected to pressure.

            Milk is a fine suspension of fat and protein globules in a watery liquid containing milk sugar (lactose) and other dissolved substances. Normally the fat is dispersed uniformly in the form of fine droplets and hence remains as an emulsion. But when milk is heated these fine droplets tend to raise up and at temperature of about  form a thick layer of cream on the surface. When milk comes to boiling, bubbles of steam formed at the bottom of the vessel rise up and force the thick creamy layer upwards causing the milk to spill.

                                    

   Soaps are salts of fatty acids. Common soaps are water soluble sodium and potassium salts of fatty acids. Soap cannot form lather unless it dissolves in water. Hard water does not dissolve soap because the calcium and magnesium salts present in it produce insoluble substances by reacting with soap. These insoluble substances separate out as scum and reduce the effectiveness of the soap as a cleansing agent.

 Synthetic fibres are made artificially. They are solid, smooth and straight in structure unlike a natural fibre like cotton which is hollow. So when synthetic fabrics are soaked in water, only the surface of the fibres gets wet as water does not enter the body of the fibre. That is why these fabrics absorb very little amount of water and dry quickly as the water drips away. Such fabrics are also known as ‘drip dry’.

            There is a close link between the sense of taste and the sense of smell. Much of what we think of as taste has a big smell component. The taste buds in the tongue monitor relatively crude sensation of the four basic tastes – sweet, salty, sour and bitter. Faint vapours of whatever we eat drift into the nasal cavity where the smell receptors add more detail to the information given by the taste buds.

When we have a cold our nose becomes blocked and the sensation of smell ceases. The gas and vapours from the food cannot be sensed by the smell receptors; consequently we cannot perceive the smell or aroma of the food, which in turn makes the food appear tasteless.

            Tears produced by the tear glands keep the eyes moist and are normally drained off through the nose. Onions contain a number of water soluble volatile substances containing sulfur. On cutting the onion these substances quickly spread into the air and cause irritation in eyes. The tear glands start secreting more and more tears to wash out the irritants. The tears are produced so rapidly that they cannot be drained out through nose and so run down the eyes.

            Sea water is salty because it contains many dissolved salts, mostly sodium chloride with small proportions of potassium, magnesium, calcium and carbonates. The salt comes mainly with river water that flows through rocks eroded by frost and rain. The gradual wearing a way of mountains releases chemicals which are carried down by rivers to the ocean as dissolved salts. Some salt also enters sea water from the rocks beneath the sea bed. The river water carrying the salts to the sea does not taste salty because the salts are present in extremely small concentration. Whereas in the case of the oceans, water is continuously evaporating even as more and more salt continues to be added with river water. This, over millions of years has led to the high concentration of dissolved salts in sea water.

            The peculiar smell is produced by the soil inhabiting bacteria called streptomycetes. Streptomycetes are abundant in dry warm soil – a million of them are present in a pinch of soil. They release compounds such as geosmin and 2-methyl isoborneol, which vapourize easily, when wetted by rain water after a dry spell. That is why we get the musty odour only after the first rain of the rainy season. The smell can be detected in a newly ploughed field also.

            The bottom of lakes and ponds, which usually hold still water, is usually covered with sediments formed of clay material. Clay contains chemical substances such as sodium bentonite which have the property of expanding when wet. The loss of moisture, therefore, makes this layer of clay shrink resulting in cracks on its surface. Thus, in summers when lakes and ponds go dry, the surface of their beds shows large cracks.

            When you meet another person, or are introduced to him, it is polite to say ‘Namaste’ with folded hands, or extend your hand for a handshake. The handshake is the universal form of greeting in the West. However, even this simple gesture varies from country to country.

            The American style handshake has a firm grip along with two quick pumps, eye contact and a smile. Variations in handshakes are based on cultural differences, not on personality or values. The Japanese give a light handshake. Germans offer a firm handshake with one pump, and the French grip is light with a quick pump. Middle Eastern people will continue shaking your hand throughout the greeting. Don’t be surprised if you are occasionally met with a kiss, a hug, or a bow somewhere along the way!