Unique Attributes of Water Chapter 2, Part 2

 Water covers 75% of the Earth’s surface.  Water is unusual because it is the only compound which exists commonly in all three states of matter.  Gas (water vapor)  Solid (ice)  Liquid (fluid water)

 Water is a critical component of living systems.  Water dominates the intracellular environment. ◦ 75-85% of the cytoplasm of a plant or animal cell is water. ◦ In some organisms, like jellyfish, this value exceeds 95%.  In many biological reactions, the H + OH - of water or are pulled off organic molecules to synthesize water.

 Individual water molecules are polar molecules because of the electronegativity difference between hydrogen and oxygen.  Because of this, water molecules easily form hydrogen bonds with other water molecules or with polar or charged compounds  One water molecule can form hydrogen bonds with up to four other water molecules.  Water has a number of interesting physical properties because of the importance of hydrogen bonds. Na + --

 At any one time any water molecule forms hydrogen bonds with several others, with bonds forming and breaking constantly (in liquid).  Cohesion is a measure of the “stickiness” among molecules of the same type. ◦ Water molecules have a high level of cohesion because of these hydrogen bonds that form among molecules.  Adhesion is the tendency of one substance to cling to another substance. ◦ Because of hydrogen bonding, water adheres to a wide variety of other substances, such as many biological molecules. ◦ But not at all to others, such as oils.

 Water has a high specific heat, which means it will absorb a lot of energy before the temperature of the water changes. ◦ It takes energy to break apart the hydrogen bonds  The specific heat of water is J/g°C, while Tungsten’s specific heat J/g°C.  Since humans are 60%, we have a high specific heat. This is why our temperature is fairly constant at 98.6°.

 A mixture is matter that contains two or more substances are not in set proportions  A solution is a liquid that contains a homogeneous mix of two or more substances. Matter Pure substances CompoundsElementsMixtures Homogenous Mixtures Heterogeneous Mixture

 Chicken Noodle Soup  Milk O2O2  Diamond  Carbon Dioxide  Salt  Salt Water  Bronze

 An aqueous solution is a solid, liquid, or gas dissolved in water.  The concentration of a solution is the relative amounts of solute and solvent. ◦ ↑ solute in solution, the more concentrated ◦ ↓ solute in solution, the less concentrated  Water (H 2 O) is a good solvent for some substances, but poor for others.  Molecules that have regions of polar covalent bond or ionic dissolve well? Or not well?  Hydrophilic (water-loving) materials where water molecules surround the materials with hydrogen bonds.

 When salt (NaCl) is added to water, groups of water molecules form _________ bonds with Na + and Cl -.  These hydrogen bonds between water and ions pull the ions _____________ from the salt.  Water’s ability to dissolve hydrophilic compounds is limited.  Eventually, there are no more __________ water molecules to form new hydrogen bonds and the solution is saturated.

 Molecules that are dominated by non-polar covalent bonds do not form hydrogen bonds and do not dissolve in water.  Examples of these hydrophobic (water-fearing) compounds are oils and fats.  Water molecules will push hydrophobic molecules together to reduce water’s surface area (lowering surface tension).  Sprinkle oil droplets on water and eventually they will ______________ into one large drop.  Hydrophobic lipids are the major constituent of cell membranes.

 Among all the molecules in 1 liter of water are a few in which oxygen has stolen the shared electrons completely from one hydrogen atom.  H 2 O⇆ H + + OH -  At any one time, 1 in every 554 million water molecules has dissociated into a hydrogen cation (H + ) and a hydroxide anion (OH - ).

 A chemical equation is a way of describing what happens in a chemical reaction.  Equation for Photosynthesis  Light + 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2  The arrow indicates the direction the chemical equation is occurring. Most often said as “yields”. ReactantsProducts

 Dehydration Synthesis Reaction is a chemical change where water is released and a larger, more complex molecule is made (synthesized).  NH 2 CH 2 CO-OH + H-NHCH 2 CO-OH →  NH 2 CH 2 CO-NHCH 2 CO-OH +H-OH

 Hydrolysis Reaction is where water is used to break the reactants into smaller, less complex products ◦ NH 2 CH 2 CO-NHCH 2 CO-OH + H-OH →  CH 2 CH 2 CO-OH + NHCH 2 COO-OH

 An acid is any substance that ________________ the [H + ] in a solution.  In water, an ionic compound, like HCl, will separate into H + and Cl - ions, increasing the concentration of H +.  Most acids are “proton donors”.  A base is any substance that _________ the [H + ] in a solution.  Some bases remove H + directly: ◦ NH 3 + H + NH 4 +  These bases are “proton acceptors  Others are more indirect:  NaOH Na + + OH - OH - + H + H 2 O

 HCl  NaOH  KOH  H 2 SO 4  CH 3 COOH

 In biological systems, the hydrogen ion concentration varies over a huge range of values, by 100 million or more. ◦ For example, the concentration of hydrogen ions in the stomach is 1,000,000 times greater than that in the _______  To encompass that range of variation (so many zeroes), the pH scale was developed.  pH = -log 10 [H + ] or [H + ] = 10 -pH  Because the pH values are measured on a log scale a change of pH from 7 to 5 represents a 100x increase in [H + ]. ◦ The change is 2 pH units: 10 2 = 100.

 A solution with a pH between 0 and 7 is acidic  A solution with a pH between 7 and 14 is basic.  The intracellular pH is  If we add acid to the solution, [H + ] will increase (the exponent will be less negative) and pH values will be smaller (moving toward 1).  If we add base to a solution, the [H + ] will decrease (the exponent will be more negative) and pH values will be larger (moving up to 14).

 Salts are ionic compounds that do not release either H + or OH - when dissolved in water. Usually a product (along with water) of a reaction between an acid and a base. In chemistry, a salt is any metal combining with a non-metal. ◦ HCl + NaOH → Na + + Cl - + H + + OH - → NaCl + H 2 0 ◦ Examples of Salts:  Potassium Chloride (KCl)  Calcium Chloride (CaCl 2 )  Copper Sulfate (CuSO 4 )

 Many normal cellular processes have the potential to release large quantities of H + or OH - ions.  Buffers are an aqueous solution that contain weak acids or weak bases that tend to maintain constant pH. This is because they can either accept or release hydrogen ions. H 2 CO 3 HCO H + Carbonic AcidBicarbonate Ion response to increasing [H + ] response to decreasing [H + ]