1. Water and Solutions Section 2-2

2. Water is a Major Component of Cells 70 % of your body is water. 2/3 of molecules in body are water. 70 % of your body is water. 2/3 of molecules in body are water. Water stores heat efficiently. Water stores heat efficiently. –Heats more slowly and retains heat longer than many other substances –Many organisms release heat through water evaporation (ex. Sweating) –In organisms, this ability to control temperature enables cells to maintain a constant internal temperature when external temperature changes drastically –WATER HELPS MAINTAIN HOMEOSTASIS

3. Water bonds to itself and to other substances Water bonds to itself and to other substances –Hydrogen bonds between water molecules cause cohesion of liquid water –Cohesion – attraction between substances of the same kind –Molecules at surface of water linked together by hydrogen bonds (like people holding hands). –This attraction between water molecules causes surface tension. Surface tension prevents surface of water from stretching or breaking easily. –Water is attracted to other polar substances –Adhesion – attraction between different substances

4. –Because of adhesion, some substances get wet. Adhesion powers the process called capillary action, in which water molecules move up through a narrow tube.

5. Water Dissolves Many Substances Solution – a mixture in which one or more substances are evenly distributed in another substance Solution – a mixture in which one or more substances are evenly distributed in another substance Polarity Polarity –Polarity of water enables many substances to dissolve –Ionic and polar molecules dissolve best in water –Ions are surrounded by water molecules –Nonpolar molecules do not dissolve well in water Do not mix Do not mix This helps shape the cell membrane and allows them to function This helps shape the cell membrane and allows them to function

6. Acids and Bases Acids and Bases Water breaks down – a tiny fraction of bonds may break, forming H + ions and hydroxide ions (OH - ) Water breaks down – a tiny fraction of bonds may break, forming H + ions and hydroxide ions (OH - ) H 2 O → H + + OH - H 2 O → H + + OH - Pure Pure water always has low concentrations of H + and OH - Compounds that form H + ions when dissolved in water – acids – increase concentration of H + in water when dissolved HCl → H + + Cl -

7. Bases – compounds that reduce the concentration of H + in solution. Forms OH - (hydroxide) ions – join with H + to make water, thus reducing the H + concentration Bases – compounds that reduce the concentration of H + in solution. Forms OH - (hydroxide) ions – join with H + to make water, thus reducing the H + concentration pH scale pH scale –Measures concentration of H + in solution –Ranges 0 to 14 –7 = neutral –Below 7 = acid –Above 7 = base