polarity of water ionic compound dissolved in water Nonionic polar molecules

Transcription

1 Fig. 3-7 polarity of water form hydrogen bonds easily versa6le solvent () () () () () () () () Cl Na Na Cl ionic compound dissolved in water each ion surrounded by a sphere of water molecules hydra&on shell Fig. 3-8 Nonionic polar molecules also dissolved by water Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions Water soluble (a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment (c) Ionic and polar regions on the protein s surface attract water molecules. 1

2 ydrophilic and ydrophobic Substances Solute Concentra5on in Aqueous Solu5ons hydrophilic affinity for water Polar or ionic Readily dissolve hydrophobic no affinity for water Difficult or impossible to dissolve il molecules nonpolar bonds A colloid is a stable suspension of fine par6cles in a liquid Most biochemical reac6ons occur in water Aqueous environments to aqueous cytosol Chemical reac6ons Due to collisions of molecules therefore depend on the concentra6on of solutes in an aqueous solu6on Concept 3.3: Acidic and basic condi&ons affect living organisms Molecular mass sum of all masses of all atoms in a molecule Mole Typical unit of measure for number of molecules Coun6ng molecules imprac6cal 1 mole (mol) = 6.02 x molecules Avogadro s number A s n and the unit dalton were defined such that 6.02 x daltons = 1 g Molarity (M) is the number of moles of solute per liter of solu6on A hydrogen atom in a hydrogen bond between two water molecules can shiq from one to the other: hydrogen ion ( ) hydrogen atom leaves electron behind transferred as a proton hydronium ion ( 3 ) The molecule with the extra proton represented as hydroxide ion ( ) molecule that lost the proton 2

3 Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed sta6s6cally rare dissocia6on of water molecules has a great effect on organisms Changes in concentra6ons of and can dras6cally affect the chemistry of a cell 2 2 ydronium ion ( 3 ) ydroxide ion ( ) Effects of Changes in p Acids and Bases Concentra6ons of and are equal in pure water Dynamic equilibrium Acids and bases are solutes alter concentra6ons of and p scale describe whether a solu6on is acidic or basic (the opposite of acidic) Acid substance that increases concentra6on of a solu6on CL Cl 2 C 3 C 3 Base substance that reduces the concentra6on of a solu6on Na Na N 3 N 4 3

4 The p Scale In any aqueous solu6on at 25 C the product of and is constant and can be wri^en as [ ][ ] = The p of a solu6on is defined by the nega6ve logarithm of concentra6on, wri^en as p = log [ ] For a neutral aqueous solu6on [ ] is 10 7 = (7) = 7 Acidic p below 7 Basic p above 7 Most biological fluids have p values in the range of 6 to 8 Fig. 3-9 p Scale 0 Buffers 1 Battery acid Acidic solution Neutral solution Basic solution Increasingly Acidic [ ] > [ ] Neutral [ ] = [ ] Increasingly Basic [ ] < [ ] Gastric juice, 2 lemon juice 3 Vinegar, beer, wine, cola 4 Tomato juice Black coffee 5 Rainwater 6 Urine Saliva 7 Pure water uman blood, tears 8 Seawater 9 10 Milk of magnesia 11 ousehold ammonia 12 ousehold 13 bleach The internal p of most living cells must remain close to p 7 Buffers minimize and concentra6on changes consist of an acid base pair that reversibly combines with Bicarbonate buffer system 2 C 3 C 3 ven cleaner 14 4

5 Threats to Water Quality on Earth Acid precipita&on rain, snow, or fog with a p lower than 5.6 caused mainly by the mixing of different pollutants with water in the air S2(g) ½2(g) ==> S3(g) 2(l) S3(g) ==> 2S4(aq) can fall at some distance from the source of pollutants Acid precipita6on can damage life in lakes and streams Effects of acid precipita6on on soil chemistry are contribu6ng to the decline of some forests Fig More acidic Acid rain Normal rain More basic Fig EXPERIMENT uman ac6vi6es such as burning fossil fuels threaten water quality C2 is released by fossil fuel combus6on and contributes to: A warming of earth called the greenhouse effect Acidifica6on of the oceans 2(l) C2(g) <==> 2C3(aq) 2C3 (C3 C3 ShiQs toward C3 Not enough C32 2 ) RESULTS Calcification rate (mmol CaC3 per m2 per day) leads to a decrease in the ability of corals to form calcified reefs [C32] (µmol/kg) 300 5

6 You should now be able to: 1. List and explain the four proper6es of water that emerge as a result of its ability to form hydrogen bonds 2. Dis6nguish between the following sets of terms: hydrophobic and hydrophilic substances; a solute, a solvent, and a solu6on 3. Define acid, base, and p 4. Explain how buffers work Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 6