Water Packet #7 Monday, January 14, 2019Monday, January 14, 2019

Introduction Most abundant liquid in the world Makes up at least half of all living organisms and up to 95% of some species. 75% of earth is submerged in water Naturally occurring water consists of 99.76% H2O Monday, January 14, 2019Monday, January 14, 2019

Water--Isotopes The remainder consists of various isotopes 2H 18O Deuterium Most often found with a normal hydrogen atom Forms HDO Occasionally, D2O is formed Both are called heavy water and have deleterious effect on living organisms. 18O Monday, January 14, 2019Monday, January 14, 2019

The Water Molecule Recall that H2O is a polar molecule This results in the ability to form hydrogen bonds and an attraction between individual water molecules Due to the opposite charges Monday, January 14, 2019Monday, January 14, 2019

The Water Molecule Monday, January 14, 2019Monday, January 14, 2019

Properties of Water I Cohesion and Surface tension Cohesion Tendency of molecules, if in substance, to hold together by mutual attraction The hydrogen bonding of water results in strong cohesion forces. Monday, January 14, 2019Monday, January 14, 2019

Cohesion & Surface Tension What does this (string cohesion forces) mean? One drop of water will assume the smallest possible area on a surface The water molecule will form a sphere Water molecules, at the surface of the drop, will be drawn together forming a skin-like layer off molecules on the surface. The force formed is called surface tension. Monday, January 14, 2019Monday, January 14, 2019

Homework Assignment Conduct experiment determining how much water can a penny hold Must use an old and a new penny Difference in composition Must complete at least 20 trials for each penny Must complete a full lab report with a 5 page background research section on cohesion forces and surface tension PAPER MUST BE SUBMITTED AT TURNITIN.COM Due 2:45pm EDT Friday September 7th 2007 Monday, January 14, 2019Monday, January 14, 2019

Surface Tension Is a measure of how hard it is to break the surface of a liquid Insects waling on the surface of water and the movement of water up plants are two biological processes that can occur as a result of the cohesive properties of water molecules. Monday, January 14, 2019Monday, January 14, 2019

Properties of Water I Adhesion and capillarity Adhesion The attraction of molecules of different compounds to one another. The ability of water to cling readily to other molecules is responsible for the upward movement of water when a small-bore tube is dipped into it. This phenomenon is called capillarity Xylem vessels of a diameter 0.02mm can, in theory, support a column of water of height 1.5m by capillary forces. Capillary forces has one of its main biological effects being the upward movement of water in the soil Monday, January 14, 2019Monday, January 14, 2019

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PROPERTY #2 Thermal Capacity/Moderation of Temperature Monday, January 14, 2019Monday, January 14, 2019

Thermal Capacity Hydrogen bonding results in the necessity of heat to cause increased molecular movement Formation of water in the gas form (steam) Heat energy first used to break hydrogen bonds Resistance to temperature change This is why the temperature of water rises only very slowly for a given amount of added heat Water has a very high specific heat And vice versa The amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1˚C Monday, January 14, 2019Monday, January 14, 2019

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Thermal Capacity II Why is the use of heat energy for breaking hydrogen bonds important? Allows thermal stability so that enzymatic reactions(biochemical reactions) in water mediums are not subjected to large temperature fluctuations and can take place at a more constant rate. If there were no hydrogen bonds, water would be a gas at most temperatures Also helps in the cooling affect Sweating Heat of vaporization Monday, January 14, 2019Monday, January 14, 2019

Density PROPERTY #3 Monday, January 14, 2019Monday, January 14, 2019

Density Water has a maximum density at 4ºC This is when water is in a liquid state H2O (l) is more dense than H2O (s) Water freezes from top downward allowing ice to form at the top Ice at top can insulate the warmer water below that layer from colder temperatures above Prevents large bodies of water from freezing solid and allowing the survival of aquatic organisms Monday, January 14, 2019Monday, January 14, 2019

Solubility PROPERTY #4 Monday, January 14, 2019Monday, January 14, 2019

Solubility Water is a versatile solvent due to its polarity Can form an aqueous solution Monday, January 14, 2019Monday, January 14, 2019

Definitions Mixture A portion of matter that can be separated into two or more substances by physical means alone Substance composed of 2 or more elements or compounds that are mixed together, but are not chemically combined A composition of two or more substances that are not chemically combined with each other and are capable of being separated. Salt and pepper Sugar and sand 1/14/2019 9:38:39 AM Monday, January 14, 2019Monday, January 14, 2019 20

Definitions II Solution A homogeneous (of uniform structure or composition throughout ) mixture of two or more substances, which may be solids, liquids, gases, or a combination of these. Homogenous mixture Sugar in water (Sugar-water) One component (Major), of a solution, is found in a greater amount Solvent One component (Minor), of a solution, is found in a lesser amount Solute Monday, January 14, 2019Monday, January 14, 2019

The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve them Negative oxygen regions of polar water molecules are attracted to sodium cations (Na+). + Cl – – Na+ Positive hydrogen regions of water molecules cling to chloride anions (Cl–). Cl– Figure 3.6 Monday, January 14, 2019Monday, January 14, 2019

Water can also interact with polar molecules such as proteins This oxygen is attracted to a slight positive charge on the lysozyme molecule. This oxygen is attracted to a slight negative charge on the lysozyme molecule. (a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva (c) Ionic and polar regions on the protein’s Surface attract water molecules. + – Figure 3.7 Monday, January 14, 2019Monday, January 14, 2019

Solubility “Likes dissolves likes” Oil and water are dislikes Polar with polar Non-polar with non-polar Oil and water are dislikes Water = polar Oil = non-polar We say that oil and water are nearly completely immiscible The oil is suspended 1/14/2019 9:38:39 AM Monday, January 14, 2019Monday, January 14, 2019 24

Other Important Points II Hydrophilic substance Water loving Has an affinity for water Hydrophobic substance Water hating Does not have an affinity for water Monday, January 14, 2019Monday, January 14, 2019

Other Important Points II Remember, most biochemical reactions occur in water It Is important to calculate the concentration of solutes in an aqueous solution Mole The number of molecules of a substance in a given mass Molarity The number of moles of a solute per liter of solution Monday, January 14, 2019Monday, January 14, 2019

DISSOCIATION Monday, January 14, 2019Monday, January 14, 2019

Dissociation (Ionization), pH & Buffers Water has a slight tendency to dissociate into ions according to the equation 2H2O  H2O+ + OH- H2O  H+ + OH- Hydronium ions and hydroxide ions In 1 liter of water, this dissociation produces 1/10,000,000 mole of hydrogen ions. Equivalent to a pH of 7 Neutral Monday, January 14, 2019Monday, January 14, 2019

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Dissociation II If the concentration of hydrogen ions is higher, 1/1000 (10-3) the pH would be 3 and the solution would be acidic An acid, therefore, is a substance that donates hydrogen ions Increases hydrogen ion concentration A base is a hydrogen ion acceptor Decreases hydrogen ion concentration Changes in concentration of ions can have a great affect on living organisms Particularly enzymes Why? Monday, January 14, 2019Monday, January 14, 2019

Dissociation III Apart from dissociating itself, water readily causes the dissociation of other substances placed in it. Making it an excellent solvent. Monday, January 14, 2019Monday, January 14, 2019

Buffers A buffer solution is one that retains a constant pH despite the addition of small quantities of acids or bases. Buffers contain both hydrogen ion donors and acceptors. Hydrogen carbonate ions may act as an acceptor or a donor Hydrogen carbonate salts and phosphate salts are responsible for the buffering of blood. pH of 7.4 Monday, January 14, 2019Monday, January 14, 2019

Osmosis More to come later Monday, January 14, 2019Monday, January 14, 2019