The Properties of Water: Biology 101

One of the first lessons any biology student learns, are the many properties of water. One way to learn this is through a series of experiments illustrating the point. Here are a series of experiments and explanations on the results and the properties they illustrate.

What would happen if…

…You filled the bottom of a balloon with water and placed a match under it. What would happen if you placed a match under a balloon with no water in it?

Answer: The balloon with the water in it will take longer to pop than the balloon without water in it.

Why?: The water in the first balloon provide a barrier against the heat of the match. Since the second balloon had no such barrier, it popped first. This illustrates the heat absorption property of water. Water is able to take in a fair deal of heat before its state changes and thus the balloon with water in it is able to hold out longer than the one without. Fire officials wet fire hazards like fields to prevent them from burning, and in nature a wet or lush plant, that is obviously moist and full of water, is harder to catch or light on fire. When we’re building a camp fire we have to look for dry sticks and brush as wet brush has a barrier of water that won’t allow easy burning.

…You dropped two drops of food coloring into a glass of cold water, room temperature water, and hot water? In which glass would the food coloring distribute evenly more quickly?

Answer: When the dye is put into the cold glass of water it slowly goes to the bottom mixing very slowly and reluctantly with the rest of the water. In the normal water the dye goes to the bottom of the glass spreading to the right and left in little puffs as it goes. In the hot water the dye spreads across the entire glass shortly after it reaches the bottom of the glass. It gradually evens out and is the first of the three glasses to have the dye spread evenly.

Why?: The property shown here is the speed at which molecules move. Molecules move more slowly in cold water and faster in hot. As such, the dye was able to spread faster in the hot water because the fast moving molecules quickly mixed it in with the water. Conversely, the dye in the cold water wasn’t able to mix in properly because the molecules of cold water move slowly. In the real world this property can be seen in large bodies of water like lakes and oceans. Deeper depths of water are colder due to the fact that cold water sinks because it is denser than hot water. This is because the molecules are closer together. Likewise, hot water rises and forms a top layer which is why lake water and ocean water is warmer near the top.

…You place a raw egg in water? An ice cube in water? What would happen if you added salt to each glass?

Answer: When the ice is placed in the water it floats, and the egg quickly sinks to the bottom of the glass. When salt is added and stirred into the water it doesn’t affect the ice, but it does affect the egg. When you put the egg in the salt water, the egg actually floats instead of sinking directly to the bottom.

Why?: The reason the egg floats with the salt is due to the polar cohesion between the salt and water that forms a sort of platform for the egg to rest on. The strong bonds between the oxygen and hydrogen atoms are able to hold the egg up instead of breaking and allowing the egg to fall through as it normally would without an added polar substance. This experiment demonstrates the cohesion property of water. Because water is polar it is able to form strong bonds, even strong enough to hold up certain objects. Take a ship on the water. Salt, another polar substance, along with water, is able to support a large ship, wood, and the like.

…You fill a glass with water and add oil. You then add detergent (soap) to the oil and water. What happens?

Answer: The oil doesn’t mix with the water. When poured into the glass the oil forms small beads that won’t intermix with the water. Shortly after, the small beads join to form a large bead of oil on top of the water’s surface.

Why?: This part of the experiment demonstrates the solvency property of water. Polar substances will mix with water, while non-polar substances will not. Since oil is non-polar it is not soluble in water. In the environment, this property is seen on animals that have waterproof coats. Oil secretions from glands in the skin allow animals like ducks, otters, even dogs to have a nice waterproof coat or feathers in the case of the duck.

Answer 2: The soap sinks to the bottom of the glass of water cutting through the oil and causing the soap and oil to mix in with the water. This has to do with the fact that detergents like soap can cut through oil and break the hydrogen bonds of water.

Why?: Detergent solutions clean the grease and oil from the surfaces we’re trying to clean. Scientifically, detergents break the hydrogen bonds of water and thus eliminate the polar property that disables non-polar substances from intermixing with it. Thus, when a detergent if added to a polar and non-polar substance, the two are then able to mix. This demonstrates the solvency and detergent effects of water. This sort of solvency and detergent interaction is the reason why a greasy pan can be cleaned using soap and water. The bonds that separate the two are broken allowing them to intermix, and allowing us to wash away the grease. This knowledge can also help to clean up oil spills or other environmental hazards that are insoluble. We also use this principle in shampoos when washing our hair.

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