What are the Properties of Water • Polarity • Attraction- cohesion, adhesion, surface tension, & capillary action • High specific heat • Density – greatest at 4oC • Universal solvent of life What is Polarity of Water • A water molecule with an uneven distribution of charges in different regions of the molecule • Water has a variety of unusual properties because of attractions between these polar molecules. – The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. Fig. 3.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings What is a Hydrogen Bond? Hydrogen bond is a weak attraction between a hydrogen atom and other atom Properties of Water Covalent bonding vs. Hydrogen bonding Hydrogen Bond Covalent Bond What is Cohesion • cohesion = water attracted to other water molecules because of polar properties What is Cohesion? Hydrogen bonds hold the • Cohesion is responsible substance together, a for the transport of the phenomenon called water column in plants COHESION • Cohesion among water molecules plays a key role in the transport of water against gravity in plants What is Adhesion? •Water attracted to other materials What is surface tension? Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion. Surface tension – Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface. – Water behaves as if covered by an invisible film. – Some animals can stand, walk, or run on water without breaking the surface. Fig. 3.3 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings What is capillary action? It is the tendency of water to rise in a thin tube. Capillary Action Because water has both adhesive and cohesive properties, capillary action is present. Capillary Action = water’s adhesive property is the cause of capillary action. Water is attracted to some other material and then through cohesion, other water molecules move too as a result of the original adhesion. Ex: Think water in a straw Ex: Water moves through trees this way What is specific heat? Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1oC. Moderates Temperatures on Earth Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air. Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature. Celsius Scale at Sea Level • What is kinetic energy? • Heat? 100oC Water boils • Temperature? 37oC Human body • Calorie? temperature • What is the difference in o 23 C Room temperature cal and Cal? • What is specific heat? 0oC Water freezes Specific heat Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for: 1. Prevention of temperature fluctuations that are outside the range suitable for life. 2. Coastal areas having a mild climate 3. A stable marine environment What is Density It when hydrogen bonds in water expand as it warms and contracts as it cools. The hydrogen bonds keeps the molecules far enough a part to make ice have fewer molecules. Solid – water molecules are bonded together – space between fixed Liquid – water molecules are constantly bonding and rebonding – space is always changing Density of Water • Most dense at 4oC • Contracts until 4oC • Expands from 4oC to 0oC The density of water: Mass-to -volume ratio of a substance; measure of how tightly matter is packed 1. Prevents water from freezing from the bottom up. 2. Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation. 3. Makes transition between season less abrupt. – When water reaches 0oC, water becomes locked into a crystalline lattice with each molecule bonded to to the maximum of four partners. – As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state. – Ice is about 10% less dense than water at 4oC. Fig. 3.5 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings What is Solvent for Life • Solution – Solute – solvent • Aqueous solution • Hydrophilic – Ionic compounds dissolve in water – Polar molecules (generally) are water soluble • Hydrophobic – Nonpolar compounds Mixtures with Water . • A solution is another name for a homogeneous mixture. • In a solution, there are two components: • A solvent is a substance in which another substance is dissolved. • A solute is the substance that is dissolved in the solvent. Copyright © McGraw-Hill Education Water and Solutions Mixtures with Water Acids and bases • Many solutes readily dissolve in water because of water’s polarity. • Substances that release H+ when they are dissolved in water are called acids. • Substances that release hydroxide ions (OH−) when they are dissolved in water are called bases. Copyright © McGraw-Hill Education Water and Solutions Mixtures with Water pH and buffers • The amount of hydrogen or hydroxide ions in a solution determines the strength of an acid or base. • The measure of concentration of H+ in a solution is called pH. • Acids have pH values < 7; bases have pH values > 7 • Buffers are mixtures that can react with acids or bases to keep the pH within a particular range. Water and Solutions Copyright © McGraw-Hill Education .