Water & Solutions

1. Water & Solutions • Water is a unique molecule necessary for life. • found in all cells and surrounds all cells

2. Polarity • an uneven distribution of shared electrons within the molecule

3. Hydrogen Bonds • a weak chemical attraction between polar molecules • the attraction between the positively charged hydrogen of water and the negative charge that exists on other polar molecules including water itself • due to water’s polarity

4. Cohesion and Adhesion • Cohesion • attraction between molecules of the same substance • Adhesion • attraction between molecules of different substances

5. Water & Solutions Hydrogen Bonding in Water See Figure 5 on textbook page 31 Is this cohesion or adhesion?

6. Surface Tension • property of the surface of a liquid to resist an external force • the surface can stretch and will not break easily • caused by cohesion

7. Water & Solutions Surface Tension

8. Capillary Action • process in which water molecules move up through a narrow tube • the attraction of water to the walls of the tube and to the other water molecules around it pulls the water up more strongly than gravity pulls it down • caused by adhesion and cohesion

9. Water & Solutions Capillary Action

10. Density • liquid water has a density of 1 g/mL

11. Solid form less Dense than Liquid form • water is rare in that its solid form (ice) is less dense than its liquid form water

12. Solid form less Dense than Liquid Form

13. Solid form less Dense than Liquid form • water is rare in that its solid form (ice) is less dense than its liquid form water • ice floats in water

14. Universal Solvent • “like dissolves like” • water is able to dissolve ionic compounds and other polar compounds, but not nonpolar compounds

15. Universal Solvent • Solution • mixture of two or more substances in which the solute molecules are evenly distributed in the solvent • Solute • substance that is dissolved • Solvent • substance that does the dissolving

16. Ionic vs. Polar vs. Nonpolar • Ionic • substances made of oppositely charged ions held together by ionic bonds • Polar • substances with charged ends held together by covalent bonds • Nonpolar • substances with no charges held together by covalent bonds

17. Water & Ionic Substances Why is water able to dissolve salt?

18. Water & Ionic Substances Salt is ionic (made of charged particles) and water is polar (has charged ends).

19. Water & Polar Substances Why is water able to dissolve sugar?

20. Water & Polar Substances Sugar is polar (has charged ends) and water is polar (has charged ends).

21. Water & Nonpolar Substances Why does vegetable oil separate from water when they are mixed in the same container?

22. Water & Nonpolar Substances Why does vegetable oil separate from water when they are mixed in the same container? Vegetable oil is nonpolar (no charged ends), and water is polar (has charged ends).

23. Specific Heat • water has a high specific heat • specific heat – the amount of heat required to raise 1 gram of a substance 1 degree Celsius • it takes a lot of energy to heat up or cool down water

24. H2O H+ + OH- hydrogen ion hydroxide ion water Water & Solutions • Pure water will ionize in the following way to create hydrogen, and hydroxide ions. • because of this, water has a neutral pH

25. Water & Solutions • pH - a system to measure the concentration of H+ ions in a solution • Acids • H+ > OH- – pH values < 7 • Bases • H+ < OH- – pH values > 7 • Neutral • H+ = OH- – pH values = 7 • pure (distilled) water

26. Water & Solutions

27. Water & Solutions • each whole number represents a factor of 10 on the scale • Ex: A solution with a pH of 5 is 10 times as many hydrogen ions as one with a pH of 6 • Ex: How much more acidic is a solution with a pH is 2 than one with a pH is 5? • 2  3 = 10 times • 3  4 = 10 times • 4  5 = 10 times • 10x10x10 = 1,000 times more acidic!

28. Water & Solutions

30. Water & Solutions • Buffers • Weak acids or bases that prevent sudden changes in pH in living organisms