Category Science

Like all other living things, bacteria need water to survive and reproduce. If foods, such as pulses and cereals, are dried, most bacteria cannot attack them, so they are very slow to decay.

Food drying is one of the oldest methods of preserving food. Since drying reduces the moisture in foods making them lightweight and convenient to store, it can easily be used in place of other food preservation techniques. In fact, one can even use drying along with other food preservation techniques such as freezing or canning, which would make the process of food preservation even better.

 Drying food is simple, safe and easy to learn. The early American settlers practiced drying food using the natural forces of sun and wind and today, the use of technology has revolutionized this method of preserving food. With modern food dehydrators, foods such as fruit leathers, fruit chips, dried nuts and seeds and meat jerky, can all be dried year-round at home. Being easy to store and carry and requiring no refrigeration makes dried foods ideal for domestic use as well as for use in the rough outdoors.

Moreover, dried foods are good sources of quick energy and wholesome nutrition, since the only thing lost during preservation is moisture. For instance, meat jerky, dried nuts and seeds are good sources of protein for a snack or a meal. The fruit leathers and chips provide plenty of quick energy. Dried vegetables, too, can be used to prepare wholesome casseroles and soups and the nutritional value can be enhanced by using the soaking water for cooking. Therefore, dried foods are an easy food option for busy executives, hungry backpackers and active women and children, all of whom can benefit from the ease of use and nutritional content of dried foods.

Because water is an excellent solvent, we very rarely find it in a pure form. Even water from the tap has tiny amounts of a number of chemicals dissolved in it. If pure water is needed, it can be obtained by distillation.

Distilled water shares a supermarket shelf with filtered water and spring water; at home, it competes with tap water. But what makes distilled water different?

People have produced distilled water since ancient times via distillation — the process of boiling water in a still, then collecting the condensed steam. Impurities get left behind when the water evaporates. This removes harmful microbes as well as harmless (and beneficial) minerals such as calcium and magnesium.

Filtering water, by contrast, removes microbes, but not minerals. Spring water passes through a natural filter of sorts — rock — and contains high amounts of minerals. Due to this mineral content, filtered water and spring water taste better than distilled water, which tastes flat and flavorless. Some claim that the lack of minerals in distilled water deprives drinkers of vital nutrients, though researchers say people get the majority of those minerals from food.

Distillation also makes water suitable for use in lead-acid batteries, automotive cooling systems and other devices where mineral buildup would cause damage. Home beer brewers often use distilled water to imitate the extremely soft water in Pilsen, Czech Republic, home of Pilsner-style beers.    

Gases, as well as solids, can be soluble. For example, fizzy drinks have carbon dioxide gas dissolved in them. Inside the can or bottle, the carbon dioxide is at higher pressure than the outside atmosphere. When the bottle is opened, there is often a loud pop or fizz as the pressure is equalized and the carbon dioxide starts to escape into the air. If left for a few hours, the drink will lose most of its dissolved gas and taste “flat”.

Seawater has many different gases dissolved in it, especially nitrogen, oxygen and carbon dioxide. It exchanges these gases with the atmosphere to keep a balance between the ocean and the atmosphere. This exchange is helped by the mixing of the surface by wind and waves.

Dissolved oxygen and carbon dioxide are vital for marine life. Marine plants use dissolved carbon dioxide, sunlight and water to make carbohydrates through the process of photosynthesis. This process releases oxygen into the water. All marine organisms use oxygen for respiration, which releases energy from carbohydrates and has carbon dioxide and water as byproducts. Marine animals with gills, such as fish, use these organs to extract oxygen from the seawater.

Some of the properties of seawater affect how much gas can be dissolved in it: Cold water holds more gas than warm water. You will have seen this with bottles of fizzy drink, which are basically carbon dioxide in water. A warm fizzy drink cannot hold its gas, so as soon as you open a bottle of it, the carbon dioxide leaves the water in a big spray of bubbles. It is less messy to open a cold bottle of fizzy drink.

Seawater with low salinity holds more gas than high salinity water. Deep water, which has a high pressure, holds more gas than shallow water. The use and creation of dissolved gases by living things can over-ride the effect of these properties. For example, warm water with lots of plankton in it can hold more carbon dioxide than cold water with few living things in it.

Carbon dioxide is one of the most important gases that dissolve in the ocean. Some of it stays as dissolved gas, but most reacts with the water to form carbonic acid or reacts with carbonates already in the water to form bicarbonates. This removes dissolved carbon dioxide from the water.

Many plants and animals use the bicarbonate to form calcium carbonate shells. When these organisms die, some of the bicarbonate is returned to the water, but a lot of it settles down to the sea bed. This process locks up, for long periods of time, carbon that originated in carbon dioxide in the atmosphere.

If the ocean and atmosphere stayed the same, there would be a balance between the concentrations of carbon dioxide in each, but carbon dioxide levels in the atmosphere are rising, so more of the gas is dissolving in the ocean.

Water molecules are attracted to each other strongly, which is why they stay as a liquid until heated to a temperature where the bonds between them are broken and they rise into the air as vapour. At the surface of still water, there are no water molecules above pushing or pulling against the surface molecules, so the surface molecules are even more strongly drawn together than usual. This causes them to act as though they form a skin over the surface. It is this effect that is called surface tension.

Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension allows insects (water striders), usually denser than water, to float and slide on a water surface.

At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). The net effect is an inward force at its surface that causes the liquid to behave as if its surface were covered with a stretched elastic membrane. Thus, the surface comes under tension from the imbalanced forces, which is probably where the term “surface tension” came from. Because of the relatively high attraction of water molecules to each other through a web of hydrogen bonds, water has a higher surface tension (72.8 millinewtons per meter at 20 °C) than most other liquids. Surface tension is an important factor in the phenomenon of capillarity.

Surface tension has the dimension of force per unit length or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the term surface energy, which is a more general term in the sense that it applies also to solids.

All living things contain a large proportion of water. For example, around two-thirds of the human body is made up of water. Although most people could survive quite a long time without food, they would die within a few days if they had no water. More of the surface of the Earth is covered by water than by land — a fact that has an enormous effect on the climate of all parts of the Earth. Although it is a simple compound of oxygen and hydrogen, water plays a very complex role on our planet.

From those simple starter organisms to the most complex plants and animals, water has played a critical role in survival ever since. In humans, it acts as both a solvent and a delivery mechanism, dissolving essential vitamins and nutrients from food and delivering them to cells. Our bodies also use water to flush out toxins, regulate body temperature and aid our metabolism. No wonder, then, that water makes up nearly 60 percent of our bodies or that we can’t go for more than a few days without it.

Besides being essential for our bodies to function, water also promotes life in numerous other ways. Without it, we couldn’t grow crops, keep livestock or wash our food (or our bodies, for that matter). Water has also advanced civilization, providing a means for travel for entire parts of the world and a source of power for factories. Because water can also exist as a vapor, it can be stored in the atmosphere and be delivered as rain across the planet. Earth’s oceans also help regulate the planet’s climate, absorbing heat in the summer and releasing it during the winter. And of course, those same oceans serve as a home for countless plants and animals.

While no one argues against the importance of water to life on Earth, it’s fair to wonder if life could exist elsewhere without it. The answer is a resounding “maybe.” Scientists are almost certain that, at a minimum, life requires a liquid of some sort to survive, with ammonia and formamide being the most promising alternatives. Both liquids have their own set of problems, however. Liquid ammonia only exists at extremely cold temperatures, making it unlikely that organisms could find the energy to support metabolism. Formamide, on the other hand, actually stays liquid over a larger temperature range than water, and like water, it’s a solvent capable of dissolving many organic materials, but so far scientists have found little evidence that the solvent could support life.

If life forms that don’t require water do exist, they’d be very different than the life found on Earth. For instance, rather than being carbon-based, such life may arise from silicone compounds. A recent study even suggests that an alternative life form might be lurking in our solar system. Researchers studying Titan, a moon orbiting Saturn, noticed that hydrogen in the moon’s atmosphere wasn’t found on the surface. One explanation for the missing hydrogen is that life forms are consuming it, just as we consume oxygen.

So far, however, we simply don’t have enough information to say whether or not life could exist without water. We know with certainty, however, that life on Earth definitely couldn’t.

In chemical terms, a solution is not the answer to a problem but a mixture of a solid substance dissolved in a liquid. The solid is called a solute and the liquid is called a solvent. Some solids dissolve very easily and are said to be soluble. Something that will not dissolve in liquid is insoluble.

Solutions are a homogeneous mixture of two or more substances. It has homogeneity at the particle level. Usually, people think of it as some liquid with either a solid or a liquid or a gas dissolved in it. However, this is not entirely true. We can also have solid solutions like alloys. For example:

Air: It is a mixture of gas in gas. Air is a homogeneous mixture of a number of gases. The two main constituents of gases are oxygen (21%) and Nitrogen (78%).

Alloys: Alloys are homogeneous mixtures of metals. They cannot be separated into their individual components by physical methods. Irrespective of that, an alloy is considered as a mixture. It is because an alloy shows the properties of its constituents and can have variable composition. For example, brass is a mixture of 30% zinc and 70% copper.

The substances that make up a homogeneous solution are called components of the solution. It has basically has two components i.e. a solvent and a solute.

Solvent: The component of a solution which dissolves the other component in itself is called solvent. A solvent constitutes the larger component of the solution. For example, a solution of sugar in water is solid in the liquid. Here, sugar is the solute and water is the solvent.

Solute: The component of the solution which dissolves in the solvent is called solute. The solute is the smaller component of the solution. For example, a solution of iodine in alcohol known as ‘tincture of iodine’, iodine is the solute. Similarly, in carbonated drinks (Soda water), carbon dioxide gas is the solute.