Properties of Water! Why Water is Special

Why do we study water properties in biology class? About 2/3 of the mass of a cell is water! Most life-sustaining reactions occur in water solutions

Polarity Polarity describes the distribution of electrons in a molecule Polar molecules have an uneven distribution of electrons. Example: Water + -

Water forms Hydrogen Bonds Hydrogen Bonds: Form due to attraction between water molecules. Not as strong as ionic/covalent bonds Water can form up to 4 hydrogen bonds at once

Properties of water Emergent Properties of water contribute to Earth’s fitness for life Cohesion/Adhesion Surface tension Specific Heat Solution pH http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.html

Water is Cohesive Cohesion: Water molecules are drawn tightly together (on the surface of a lake or a pond, this forms a film, which is called surface tension) Explains why: Water beads on a surface (like the lab table) Insects can walk on water

A Cool Example of Cohesion / Surface Tension: Water Strider Insect Water Strider - Video http://news.nationalgeographic.com/news/2003/08/0806_030806_skeeters.html YouTube: Surface Tension YouTube: Jesus Lizard

Water is Adhesive = Adhesion = Water adheres (sticks) to different surfaces Ex: Measuring water in a graduated cylinder Water adheres (sticks) to the glass more than it adheres to itself. Why is this property of water important to organisms? Allows water to move through bloodstream.

Cohesion Adhesion Ex: Water Bubble Ex: Water on a Leaf Surface Tension and Adhesion

Water can undergo Capillary Action Capillary Action= Water can flow up a tube, against gravity Ex: Plants absorbing water through their roots (Transpiration)

Specific Heat Is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC Water has a high specific heat which allows it to minimize temperature fluctuations to within limits that permit life Heat is absorbed when hydrogen bonds break Heat is released when hydrogen bonds form

Moderation of temperature Water’s high specific heat Change temp less when absorbs/loses heat Large bodies of water absorb and store more heat  warmer coastal areas Create stable marine/land environment Humans ~65% H2O  stable temp, resist temp. change

High Heat of Vaporization Amount of energy to convert 1g or a substance from a liquid to a gas In order for water to evaporate, hydrogen bonds must be broken. As water evaporates, it removes a lot of heat with it. Sweating cools the body as heat energy from the body changes sweat into a gas 1

Moderation of temperature Evaporative Cooling Water has high heat of vaporization Molecules with greatest KE leave as gas Stable temp in lakes & ponds Cool plants Human sweat

Water has a High Heat Capacity Water absorbs a lot of heat from the air without having a large temperature change So…lakes and oceans often stabilize air temperatures Water absorbs heat when it evaporates; this is why sweating helps us cool down!

Which is ice and which is water? Water is Less Dense as a Solid Which is ice and which is water? 1

Water is Less Dense as a Solid Ice 1

States of Matter Liquid Gas Solid

Water is less dense in its solid form Water is less dense in its solid form than it is in its liquid form (Ice floats!) Why might it be a bad thing for ice to sink in a pond?

Moderation of temperature Insulation by ice – less dense, floating ice insulates liquid H2O below Life exists under frozen surface (ponds, lakes, oceans) Ice = solid habitat (polar bears)

So why does it take so much heat to increase the temperature of water?! You have to break the hydrogen bonds between water molecules first!

Solutions and Mixtures A mixture is a substance that is made of two or more elements physically mixed together Example: Mixing Skittles and M&Ms together A solution is a type of mixture where one substance is dissolved in another. Solute- the substance that is dissolved Solvent- the substance that does the dissolving

Water as a solvent Water is often referred to as the “Versatile Solvent” because of it’s ability to dissolve such a wide variety of substances. GO WATER!!!

Solution The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them

Solvent of life Hydrophilic Hydrophobic “like dissolves like” Affinity for H2O Repel H2O Polar, ions Nonpolar Cellulose, sugar, salt Oils, lipids Blood Cell membrane

Water Has a Neutral pH pH: measure of how acidic or basic a solution is scale is 0 to 14 If pH = 7, then substance is neutral (not acid or base)