Name _________________________ Date ______________ Class _____________ Biology With Weiss: Properties of Water Water’s chemical formula is H2O. That is, one atom of oxygen is bonded to two atoms of hydrogen. The hydrogen atoms are “attached” to one side of the oxygen atom, resulting in a water molecule having a positive charge on the two hydrogens and a negative charge on the other side, where the oxygen atom is found. This separation of charge on opposite ends of the molecule is called polarity. So, water is called a polar compound. Since opposite electrical charges are attracted to one another, water molecules tend to be attracted to each other. This makes water molecularly “sticky.” The hydrogen end of the water molecule (positive charge) is attracted to the oxygen end of another water molecule (negative charge.) So, water “sticks” to other water molecules. This property of water is known as cohesion. All these water molecules attracting each other mean they tend to clump together. This is why water forms large drops. If it wasn’t for gravity, these drops would be ball shaped or spherical (in fact, they are this shape, in outer space!) This stickiness also allows water to stick to other substance. This is called adhesion. This only happens if the other substance or thing is also polar. Blood, which is 90% water, “sticks” to the walls of our blood vessels because of adhesion. This allows blood to flow through our body as one continuous “tube.” Water is also known as the “universal solvent” because it dissolves perhaps more substances than any other liquid on Earth. This means that wherever water goes, either through the ground, lakes, oceans, or the bodies of living things, it carries valuable chemicals, like nutrients, minerals, and gases. That’s called transport! Ever wonder, how some insects walk across the surface of a pond without sinking? The surface water has an incredible property. On the molecular scale, it acts like a stretched elastic membrane or “skin.” This property is referred to as surface tension and is largely due to cohesion between adjacent water molecules. It is caused by the attraction of the water molecules on the surface layer. The whole effect causes a “tightness” at the surface. Water has other amazing properties. When it is a solid, it is LESS dense than its liquid form. No other substance is like this. This is why ice floats on water. (You knew that) This is particularly important for aquatic life during freezing temperatures. The aquatic life can live below the ice layer and survive! And finally, water is a great coolant and regulator of temperature. When the water in sweat evaporates, it leaves behind less heat energy. That means that coolness takes its place. So, the temperature on the surface of the skin goes down, slowly cooling the body. This is known as evaporative cooling. Water also has a high specific heat. Part One: Water on Penny Materials: Dropper bottle Water Penny 1. Prediction: How many drops of water can pile on a penny before it overflows? _____________ 2. Let's see how many drops of water you can you place on the surface of a penny before it overflows. Drop water from the dropper onto a penny, keeping careful count of each drop. Table 1. Number of Drops Predicted Trial 1 Trial 2 Trial 3 Trial 4 Average Number Part 2: Water on Penny – Effect of Liquid Detergent Materials: Dropper bottle Water Penny Detergent (soap) 1. With a Q-tip applicator, spread a small amount of detergent, enough to just cover the surface of a dry penny. 2. Prediction: How many drops do you think this penny will hold after being smeared with detergent, more, less, or the same as before? Why? 3. Using the same dropper as before, add drops of water to the penny surface. Keep careful count of the number of drops. Table 2. Prediction of # of Drops of Water on a Penny with Detergent Trial 1 Trial 2 Trial 3 Trial 4 Average Number of Drops Part Three: Paper Clip Materials: Paper clip Cup/Beaker Water String (if needed) 1. Using a steady hand and a piece of string, see if you can get the paper clip to rest on the surface of the water in such a way that it will not sink Part Three: Celery and Colored Water Materials: Water With Food Coloring Cup/Beaker Celery Stalk 1. Fill the about half of the cup/beaker with the colored water. 2. Insert the stalk of celery. 3. Wait 24-48 hours. Results: Part Four: Water Glue Materials: Water dropper 2 Microscope Slides 1. Place two drops of water on one slide. 2. Place the other slide on top of that slide. 3. Try to separate the two slides. Results: Part Five: Dragging Water Part Six: Dissolving Differences Materials: 2 Small Beakers 50 mL Water 50 mL Alcohol 2 teaspoons Salt 1. 2. 3. 4. Measure 50 mL of water and put in cup A. Measure 50 mL of rubbing alcohol and put into cup B. Place 1 spoonful of salt in each of the cups at the same time. Use the stir rod to swirl contents in the cup at least 3 times. Observe for 1 minute then record your observations below:
