Properties of Water Unit 2 Lesson 2

 Water is one of the few compounds found in a liquid state over most of Earth’s surface.  Water (H 2 O) is neutral. The positive charges on its 10 protons balance out the negative charges on its 10 electrons. The Water Molecule

 Cohesion is an attraction between molecules of the same substance.  Cohesion is the force that causes water molecules to stick together. That is why drops of water form on a smooth surface.  Cohesion is also the force that causes surface tension. Cohesion

 Adhesion is the attraction between molecules of different substances.  Adhesion is what causes water to form a meniscus in a graduated cylinder. Adhesion

 Adhesion between water and glass also causes water to rise in a narrow tube against the force of gravity. This effect is called capillary action.  Example of Capillary Action: Water traveling through the roots of plants into stems and leaves. Adhesion

 Water is not always pure. It is often a part of a mixture.  A Mixture is composed of two or more elements or compounds that are physically mixed together.  Living things contain many mixtures that involve water. EXAMPLE: Blood, Saliva, Tears  Two types of mixtures that can be made with water 1. Solutions 2. Suspensions Solutions and Suspensions

 A solution occurs when ions slowly spread out in water.  Example: If you add salt “NaCl” to water, the sodium and chloride ions break apart and are attracted to the water molecules. Solutions

 Solutions contain two components: 1.Solute- The substance that is dissolved 2.Solvent- The substance in which the solute is dissolved in. Solutions

 Chemists developed the pH scale to indicate the concentration of H+ ions in solution.  The pH scale ranges from 0 to 14.  At a pH of 7, the concentration of H + ions and OH – ions are equal. Pure water has a pH of 7. The pH Scale

 Solutions that have a pH below 7 are called acidic.  Acidic substances have more H+ ions than than OH- ions.  The lower the pH the greater the acidity.  Solutions that have a pH above 7 are called basic.  Basic substances have more OH- ions than H+ ions  The higher the pH the more basic the substance. pH Scale

 An acid is any compound that forms H+ in solution.  Acids have a pH value below 7.  Common examples of acidic substances: Stomach Acid- pH of 1 Vinegar- pH of 3 Citrus Fruit- pH of 2 Soda- pH of 3 Acids

 A base is a compound that produces hydroxide (oH-) ions in solution.  Bases have a pH value above 7.  Common examples of basic substances: Baking Soda- pH of 9 Drain Cleaner- pH of 13 Ammonia- pH of 11 Bases