3Unique Properties of Water: Most abundant compound in nearly all living things
4Unique Properties of Water: Density of solid water vs. liquid waterExpansion on freezing – water forms a crystalline structure that expands and is less dense than its liquid state
5Unique Properties of Water: Covers more than 75% of the Earth’s surfaceWater 100°C or 212°FWater 0°C or 32°FUniversal solvent
6Unique Properties of Water: Water has a high heat capacityHeat capacity = the amount of heat energy required to increase its temperature, is relatively high.Large bodies of water (oceans and lakes) can absorb large amounts of heat with only small changes in temperature.This protects organisms living within from drastic changes in temperature.
7What is a polar molecule? An uneven distribution of electronsThe molecule becomes chargedon each endIt means that the electrons areNOT shared equally
8Hydrogen BondingBecause of their partial positive and negative charges, polar molecules such as water can attract each other.The attraction between a hydrogen atom on one water molecule and the oxygen atom on another is known as a hydrogen bond.
9Interaction Between Water Molecules Negative Oxygen atomof one water molecule is attracted to the Positive Hydrogen atom of another water molecule to form a HYDROGEN BOND
11CohesionCohesion is when one water molecule sticks to another water molecule due to hydrogen bondingIt creates surface tension (a measure of strength) at the surface of the liquidProduces a surface “film” that allows small insects to “walk on water”
12Surface TensionA measure of how difficult it is to break the surface of a liquid because of hydrogen bonds.The surface tension of a liquid results from an imbalance of intermolecular attractive forces, (cohesive forces) between moleculesA molecule in the bulk liquid experiences cohesive forces with other molecules in ALL directions.A molecule at the surface of a liquid experiences only NET INWARD cohesive forces.
13Adhesion Adhesion is when a water molecule sticks to another substance (NOT another water molecule)A piece of tape adheres to the wallCapillary action is an example of adhesion (water moving from the roots, through the stem, & into the leaves of a flower)
14Capillary ActionWater climbing up a small tube because of the adhesion to the sides and the cohesion between water molecules.
15Adhesion Also Causes Water to … Attach to a silken spider webhold onto plant leaves
16Cohesion and AdhesionMercury does not wet glass - the cohesive forces within the drops are stronger than the adhesive forces between the drops and glass. When liquid mercury is confined in a tube, its surface (meniscus) has a convex shape because the cohesive forces in liquid mercury tend to draw it into a drop.When liquid water is confined in a tube, its surface (meniscus) has a concave shape because water adheres to the surface and creeps up the side.
17High Heat CapacityWater’s heat capacity, the amount of heat energy required to increase its temperature, is relatively high.Because of the multiple hydrogen bonds between water molecules, it takes a large amount of heat energy to cause those molecules to move faster and raise the temperature of the water.Large bodies of water, such as oceans and lakes, can absorb large amounts of heat with only small changes in temperature. This protects organisms living within from drastic changes in temperature.
18Universal Solvent Hydrophilic Hydrophobic A substance that is attracted to water (a polar molecule)Examples: sugar, alcoholHydrophobicA substance that repels (is afraid of) water (a nonpolar molecule)Examples: oilThe Chemistry of Water
19Solutions and Suspensions MixturesSolutions and Suspensions
20What is a Mixture?Substance composed of two or more elements or compounds that are mixed together, but NOT chemically combined.Mixture Examples: salt & pepper; sugar & sand; salt & sand; Earth’s atmosphere; soil
21Solutions and Suspensions Mixture – a material that consists of 2 or more elements or compounds physically mixed together but are not chemically combined.
22Homogeneous Mixture (Solution) Homogeneous mixture in which one substance is dissolved in anotherExamples: sugar in water; salt in water; hot chocolate; tea, Kool-aidSalt Dissolving in Water
23Parts of a Solution All solutions contain a solute and a solvent. Solvent is the substance doing the dissolving.Example: waterSolute is the substance that is being dissolved.Example: salt
24Heterogeneous Mixture (Suspensions) Mixture of water and non-dissolved materials (heterogeneous)Examples: blood; oil and water
25Application: 1 – Choose one of your examples of a solution. Explain how the parts(components of the solution) can beseparated.2 – For the same example, identify thesolute and solvent in the solution.Explain your reasoning.
26Example of a Solution: Water is the universal solvent. The solute (sugar) dissolves in the solvent (water).The solute (Kool-aid) dissolves in the solvent (water).The solute (oxygen) dissolves in the solvent (nitrogen).Water is the universal solvent.
27Homeostasis a. Makes a good insulator b. Resists temperature change Ability to maintain a steady state despite changing conditionsWater is important to this process because…a. Makes a good insulatorb. Resists temperature changec. Universal solventd. Coolante. Ice protects against temperature extremes (insulates frozen lakes)4
28Acids, Bases, pH, & Buffers All about the pH Scale
30Acids Compounds that release H+ into solution H+ = hydrogen ion If [H+] > [OH-] then thesolution is acidic.HCl H+ + Cl-
31Bases If [OH-] > [H+] then the solution is basic Compounds that releaseOH- into solutionOH- = hydroxide ionIf [OH-] > [H+] then thesolution is basicNaOH Na+ + OH-
32The pH scale (power of Hydrogen) as in Hydrogen ions Measures the relative concentration of H+ and OH-
33Interpreting the pH Scale pH is based on a logarithmic scaleA pH of 5 is 10× more concentrated than a pH of 6 (in terms of H+ concentration)A pH of 9 is 100× more concentrated than a pH of 11 (in terms of H+ concentration)
34Classifying Acids & Bases Strong acids have a pH value between 1-3Weak acids have a pH value between 4-6Bases:Strong bases have a pH value between 12-14Weak bases have a pH value between 8-11
35BuffersWeak acids or bases that can react with strong acids or bases to prevent sharp sudden changes in pHProduced naturally by the body to maintain homeostasisThe pH value in most cells isThe pH of stomach acid is 2The pH of the blood is 7.4
36Blood Buffer – pH needs to be 7.4 Double arrows meanreactions are inequilibriumbicarbonate ion (buffer)(Kidney – carriedaway in urine)Free hydrogen ionsCarbonic Acid(Lungs – carriedaway as CO2)
37Blood Buffer – pH needs to be 7.4 You can see that if the reactions go to the right, hydrogen ions are released, making the solution more acidic, and if the reactions go to the left, hydrogen ions are sucked up, making the solution more basic. The question that is probably eating away at you right now is: "how do I know which way the reactions are going to go-- to the right or to the left?“Good question! The bicarbonate ion isn't a very strong acid or base. It doesn't have to go one way or the other all the time. Instead, the direction it goes depends on the solution it is in. You see, if it is in an acidic solution, there are lots of hydrogen ions floating around; in this situation, the presence of tons of hydrogen ions will force the reaction to go to the left. Do you see why? Look at the reaction again. All you need for the reaction to be able to go to the left is available hydrogen ions (see the H+ in the middle that is needed for the reaction to go to the left?). So if bicarbonate ions find themselves in acidic solutions, they tend to act like the weak base they can be, and suck up the excess hydrogen ions.Consider what will happen if bicarbonate is put into a basic solution. A basic solution has very few hydrogen ions floating around. In this condition, the bicarbonate reaction cannot proceed to the left, since no hydrogen ions are available. Instead, it will go to the right, producing hydrogen ions. In this manner, bicarbonate ions will tend to act like the weak acid they can be, and release hydrogen ions.
38Use the structure of a water molecule to explain why it is polar. Why is water such a good solvent?What is the difference between a solution and a suspension?How do hydrogen bonds between water molecules occur?How does the body counteract a drop in blood pH during strenuous exercise?If a strong acid is dissolved in pure water will the pH of the solution be greater or less than 7?
39Water ChemistryPlease draw the structure of a water molecule (H2O).Label the charges on the molecule that make it polar (negative and positive ends).See if you can connect the water molecule that you drew to two other molecules of water using hydrogen bonds.Can you think of any unique properties that water displays?
40Water ChemistryExplain why water is “polar” in your own words.Explain capillary action in your own words.Explain surface tension in your own words.
41According to the scale, what substance is neutral? What solution has an [H+] of 0.01?Which substance produces the most OH- ions in solution?How many more times basic is pH 14 compared to pH 11.