1. Properties of Water Chapter 2-2

2. The Water Molecule  Water covers ¾ of the Earth’s surface  Single most abundant compound in living things  Expands as it freezes  One of few compounds that is a liquid at the temperatures found on Earth

3. Polarity  Electrically neutral  O has a greater attraction for electrons than H H O H

4.  Shared e- spend more time around O  O has a negative charge, H a positive charge  Known as a polar molecule because of the uneven distribution of electrons

5. Hydrogen Bonds  Because of their partial + and – charges, H 2 O molecules can attract each other  Hydrogen bonds form between O and H atoms of different molecules  Weaker than covalent or ionic bonds

6. Properties of Water  A single H 2 O molecule can be involved in 4 H bonds at the same time  The ability to form multiple bonds is responsible for many of water’s properties

7. Cohesion  Cohesion – attraction between molecules of the same substance  H 2 O is extremely cohesive because of H bonds  Causes water to form beads/drops  Why some insects & spiders can walk on H 2 O

8. Adhesion  Adhesion – attraction between molecules of different substances  Causes H 2 O to travel up the sides of a graduated cylinder ( read at meniscus)  Adhesion is stronger than cohesion  Responsible for capillary action

9. Solutions and Suspensions  Mixture – material composed of 2+ elements  Physically combined not chemically  Can separate out individual components  2 types of mixtures – solutions and suspensions

10. Solutions  Molecules are evenly distributed in a liquid  Examples: salt and water, Kool Aid  Solution has 2 parts: solvent and solute

11.  Solvent – liquid that does the dissolving  Solute – substance that is dissolved  Water can dissolve most things Known as the “universal solvent” Known as the “universal solvent”

12. Suspensions  Mixture of H 2 O and non-dissolved materials  Undissolved particles remain suspended in liquid ( don’t settle out)  Examples: blood and some liquid antibiotics

13. Acids, Bases and pH  Water molecules can react to form ions  H 2 OH + + OH –  Waterhydrogen ion + hydroxide ion  Because the number of + ions and –ions produced are equal, water is neutral

14. The pH Scale  Scale devised by chemists to indicate the concentration of H + ions in solution  pH scale ranges from 0 to 14, with 7 being neutral  At a pH of 7, there are equal numbers of H + and OH - ions

15.  Solutions with a pH below 7 are acidic They have more H + ions They have more H + ions The lower the pH, the greater the acidity The lower the pH, the greater the acidity  Solutions with a pH greater than 7 are basic Have more OH - ions Have more OH - ions The higher the pH, the more alkaline The higher the pH, the more alkaline  Each step on the pH scale represents a factor of 10

16. Acids  Acid – any compound that will form H + ions in solution  Have pH values below 7  Contain higher concentrations of H + than H 2 O  Strong acids tend to have a pH of 1-3 HCl, stomach acid, has a pH between 1 and 2 HCl, stomach acid, has a pH between 1 and 2

17. Bases  Bases – a compound that produces OH - ions in H 2 O  Basic, or alkaline, solutions have lower concentrations of H + than water  Have pH values above 7 Strong bases, like lye, have pH values between 11 and 14 Strong bases, like lye, have pH values between 11 and 14

18. Buffers  Buffers – weak acids and bases that react with strong acids and bases to prevent a sharp, sudden change in pH  Used in the body to help control overall pH Body pH range is 6.5 to 7.5 Body pH range is 6.5 to 7.5  Controlling pH is important for maintaining homeostasis