The Science of Water

1. The Science of Water

2. Water of various qualities exists worldwide, and the quality of that water determines its uses. Throughout this unit you will learn how the properties and quality of water relate to everyday life.

3. We will begin by studying some of the key properties of water, including solvency, polarity, adhesion, surface tension, cohesion and capillary action, so we understand why water becomes easily polluted. WATCH: The Chemistry of Water here!

4. Water as a solventTo understand why water is such a good solvent we need to talk about its polarity. Water is a polar molecule. Have you ever heard the saying "Opposites attract"?One end of the water molecule has a slight negative charge and the other end has a slight positive charge Water is a good solvent for other polar molecules. It’s such a good solvent it’s often called the ‘Universal Solvent’. When water is mixed with another polar molecule they form a solution. Water is not a good solvent for molecules that aren't polar. This is why life is possible on Earth. Or anywhere! Water brings together the substances needed for life. This is also why water is so easily polluted!

5. Try this experiment. Take a sharpie and draw a small line on your finger. Try to wash it off with water. What happens? It won't come off because water is polar and the ink is not. Now try washing it off with some rubbing alcohol. What happens? The line comes off more easily because the alcohol is non –polar and so is the ink.

6. Try this experiment Look at the bottle of oil and water. Where is the water? Where is the oil?What happens when you shake the bottle? What does this tell you about oil? Oil is non-polar so it is not soluble in water. This is why they don’t mix. Oil is lighter than water so it floats. When you shake it goes into solution and forms little balls. (It’s trying to hide from the water!)

7. Think about this: What happens when we add detergent to a sink full of greasy dishes? Why? Detergent molecules have polar ends, which love water and non-polar ends, which love grease. When we mix the water, oil and detergent, the non-polar end of the detergent becomes embedded in the grease ball (like dissolves like) leaving all the polar ends of the detergent facing the water. The small droplets of oil have become surrounded by the detergent. The surface of this new "fuzzy" grease ball is the polar ends of the detergent. The detergent helps the water and oil mix.

8. Homework Polar and Non-polar Molecules Worksheet

9. Solvent – noun having the power of dissolving; causing solution. a substance that dissolves another to form a solution: Water is a solvent for sugar.

10. Polarity – noun the positive or negative state in which a body reacts to a magnetic, electric, or other field.

11. There are two types of covalent bonds, polar and non-polar. Water is a POLAR molecule.Molecules joined by polar covalent bonds are not "sharing" the electrons evenly and will have resulting areas of partial charge. Alcohol is a NONPOLAR molecule. Molecules joined by non-polar covalent bonds are "sharing" the electrons evenly and will not have areas of partial charge.

12. Solution – noun a physical combination or molecular mixture of two or more substances.