Here is part 1 of this series
1. Why don’t oil and water mix?
When oil is poured on water, the oil rises to the top and does not mix with the water. A phenomenon called polarity causes these molecules to repel one another. In atoms, the positive electrical charge of the nucleus is balanced by the negative charge of the electrons: as a result, atoms have no net electrical charge. But in molecules, formed when atoms link up, one end of the molecule may have a positive charge and the other a negative charge, resulting in an unequal charge. Molecules possessing this electrical imbalance are said to be polar; molecules with no such imbalance are called nonpolar. Water consists of polar molecules because the oxygen atom has a partial negative charge and the hydrogen atoms a partial positive charge. On the other hand, oil molecules, composed mainly of carbon and hydrogen are nonpolar, because they have the same positive charge everywhere. Polar molecules mix together because their positive and negative regions attract one another. Nonpolar molecules also attract one another but not as strongly. When a polar and a nonpolar substance are mixed together, the mutual attraction of the polar molecules squeezes out the nonpolar molecules, which are also drawn to one another. In this way, two substances remain separate.
2. How does soap remove dirt?
The simple act of washing one’s hands or clothing in soap and water involves chemical interactions at the molecular level. Typically, the dirt in clothes includes both dust from the air and greasy matter from the body. Because water is polar, that means it has a small electrical charge, and oil is non-polar or has no charge, the two substances do not mix, and water alone can’t remove oily dirt. But the soap molecule has both a polar end, known as hydrophilic or water-soluble and a non-polar hydrophobic or non-soluble end .
Working together the two parts remove dirt. The non-polar hydrophobic ends in the soap molecules absorb, or cling to the non-polar oily dirt molecules. At the same time, the hydrophilic ends completely surround the oily dirt particles, forming sphere-like structures called micelles. The surrounded dirt molecules are held in suspension in the water and prevented from reattaching themselves to the fabric. Rinsing away the soapy water removes the dirt molecules suspended in it.
3. How is drinking water purified?
The purification of drinking water proceeds in several stages. The first step is sedimentation, in which large particles suspended in the water settle to the bottom. The second is filtration, in which suspended solids and harmful bacteria are strained out. In the third stage, chlorine, a powerful disinfectant, is added to the water to kill the remaining microorganisms.
Unfortunately, chlorine can give water a bad taste and in large doses can even cause serious health problems. A substitute used in some countries is ozone, a safe, tasteless gas consisting of three oxygen atoms bound together. But because ozone’s germ-killer power does not last long, a tiny amount of chlorine must still be added for long –term disinfection. How ozone works--- An electrical discharge turns three molecules into two ozone molecules. In water, ozone splits into oxygen atoms and molecules that kill germs.
4. Why is flour cooked?
A major component of flour is starch, which consists of long chains of glucose molecules bound together. When raw, these chains form a rigid pattern, known as beta-starch, that resists digestion by the body’s enzymes. But when the starch is boiled with water, or baked as loaf of bread, its crystalline structures begin to break down. Water molecules seep in between the glucose molecules, giving the starch a pastelike consistency called alpha-starch. Since enzymes can break down the alpha-starch, the flour is much easier to digest.
Unfortunately, alpha-starch returns to the beta-starch stage when the temperature falls and the moisture evaporates. This tendency, known as the aging phenomenon of starch, produces a hard form of beta-starch as in stale bread that is once again difficult to digest.
5. Are all sour food acidic?
Not all sour food can be classified as acidic, even though they may appear to be at first. The lemon, for example, tastes sour and tests highly acidic, but it is classified as a basic or alkaline food. The lemon’s high content of sodium, potassium, calcium and magnesium- substances that, when mixed with water, show up as alkaline in laboratory tests-is the cause for the rating. Conversely, foods that contain substances such as chlorine, phosphorus or sulfur, all of which show acidity when they are mixed with water, are categorized as acidic. Such foods include carrots and spinach.
To determine if a food is acidic or alkaline, scientists heat it until all that remains are ashes- a process that mimics the digestive process that occurs in humans. Then they dissolve the ashes in water and measure the acidity of the solution, determining its pH value.
The pH value :
The pH scale which ranges from 0 to 14, upto 7 is neutral. Foods with a low pH value are acidic, while those high values are alkaline. The pH of human blood is 7.4, which is nearly neutral. Milk measures an acid 6.5, oranges 3.5, Ammonia registers an alkaline value of 12.
6. Why foods have different freezing points:
The freezing rates of various foods differ depending on their moisture contents. At –15 degreeC, or 5 degreeF, 93 % of the milk and 88 % of the onion-two foods with a high water content will freeze. At the same temperature, only about 78% of the apple and 73% of the orange and 65% of the banana frozen.