CH03_2_ - Overview of Water Water Hydrogen bonding of water...

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Unformatted text preview: Overview of Water Water Hydrogen bonding of water molecules with each other molecules with each other Solvent properties Solutions Units of concentration: molarity Bio 230, Summer 2010, Ch 3, Page 1 Overview of Water Water Acids and Bases pH Buffers Hydrogen Bonding All life on Earth depends on water water Most cells are 70% - 90% water Bio 230, Summer 2010, Ch 3, Page 2 Hydrogen Bonding One water molecule can form H-bonds with four other water bonds with four other water molecules molecules Each O associates with two H’s; each H associates with one O Each O has twice as much - charge as each H has + charge Fig. 3-1: Hydrogen Bonding in Water 3- - + - - + - + + + + + Bio 230, Summer 2010, Ch 3, Page 3 Hydrogen Bonding At 37oC, 15% of water molecules are in this configuration When frozen, all water molecules molecules are in this configuration Fig. 3-5: Ice versus Water 3- (100%) (37%) Bio 230, Summer 2010, Ch 3, Page 4 Ice Water Steam Properties Derived from Hydrogen Bonding Cohesion and Adhesion High Specific Heat High Heat of Vaporization Heat of Vaporization Expansion upon Freezing Bio 230, Summer 2010, Ch 3, Page 5 Cohesion and Adhesion Fig. 3-3 3- Cohesion and Adhesion Fig. 3-2 3Bio 230, Summer 2010, Ch 3, Page 6 Expansion Upon Freezing Water Benzene Solvent Properties A solvent is the liquid part of a solution A solute is a compound, usually a solid, dissolved within the the solvent Bio 230, Summer 2010, Ch 3, Page 7 Solvent Properties A solution is a homogeneous mixture mixture of individual molecules within a liquid If individual molecules don’t separate, then the mixture is a colloid, emulsion, or suspension Solvent Properties Solvent: Solute: Solution Colloid Bio 230, Summer 2010, Ch 3, Page 8 Solvent Properties Water can dissolve most ionic and polar solutes Water can’t dissolve most nonnon-polar solutes Fig. 3-7: 3Dissolving a Ionic Substance in Wate Water Bio 230, Summer 2010, Ch 3, Page 9 Dissolving a Polar Substance in Water H O H H + + H Methyl Alcohol Fig. 3-8: 3Dissolving a Protein in Water C+ O + H - - O H H H - - - - + + + + Bio 230, Summer 2010, Ch 3, Page 10 Solutions Hydrophobic: “water“waterhating”; most non-polar most non polar substances substances Fats, oils, waxes, benzene, ether Solutions Hydrophilic: “water-loving”; “watermost polar and ionic most polar and ionic substances substances Salts, many sugars, carbon dioxide, ethyl alcohol, acetic acid Bio 230, Summer 2010, Ch 3, Page 11 Solutions Hydrophobic and hydrophilic substances usually don’t form a substances usually don form solution solution Oil and water form a two-phase twosystem, with least dense material floating floating on top Solutions 2-Phase System Hydrophobic Hydrophilic Cell Oil Water Hydrophobic Membrane Bio 230, Summer 2010, Ch 3, Page 12 Hydrophilic Solutions Solutions Mole: the amount of a subsubstance equal to its molecular stance equal to its molecular weight weight in grams 1 mole of NaCl = 23+35 = 58 gms Most biological solutions have concentrations in the millimolar (mM) range One Mole Each Bio 230, Summer 2010, Ch 3, Page 13 Solutions The concentration of a solute is is in units of moles per liter: (M/L = M) One mole of any substance 23 contains 6.02 x 1023 molecules (Avogadro’s number) Units of Concentration Non-scientific Non lbs/gal, oz/qt, gms/L Scientific moles/L = molar = M Advantage of molar units specifies the number of molecules in solution Bio 230, Summer 2010, Ch 3, Page 14 Units of Concentration Examples 1.0 molar NaCl has 6x1023 molecules of NaCl per liter 0.001 molar CO2 has 6x1020 molecules of CO2 per liter of CO per liter Acids and Bases One of every 556 million water molecules exists in ionic water molecules exists in ionic form: form: H+ and OH H2O H+ + OHIn solution, acids increase the In solution, acids increase the amount amount of H+ and decrease the amount of OH HA H+ + ABio 230, Summer 2010, Ch 3, Page 15 Acids and Bases In solution, bases lower the In bases amount of H+ and raise the and amount of OH B-NH2 + H+ B-NH3+ BOH B+ + OH-, then OH- + H+ H2O Strong Acids & Bases A strong acid or base dissociates strong acid or base dissociates completely completely HCl H+ + Cl NaOH Na+ + OHNaOH OH Bio 230, Summer 2010, Ch 3, Page 16 Weak Acids & Bases A weak acid or base does not weak acid or base does not dissociate dissociate completely H2CO3 H+ + HCO3 NH3 + H+ NH4+ Buffers Weak acids and weak bases can be used as effective buffers be used as effective buffers Strong acids and bases make poor buffers Buffers control pH by absorbing Buffers excess H+ or OH- Bio 230, Summer 2010, Ch 3, Page 17 Buffers Example: Carbonic acid is the buffer that helps keep the blood at buffer that helps keep the blood at pH pH 7.4 H2CO3 H+ + HCO3HCO add base (OH-) add acid (H+) Most buffers are effective only over at range of 2 pH units pH The pH scale measures the acidity or basicity of solution; acidity or basicity of a solution; it it describes the concentration of H+, also written as [H+] The pH scale is logarithmic; The each pH unit represents a 1010fold change in [H+] Bio 230, Summer 2010, Ch 3, Page 18 0- Fig. 3-9: pH 3Scale 7- 14- Fig. 3-9: pH Scale 3- 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Neutral [H+] = 10-2 M/L +] = 10-7 M/L [H+] = 10-10 M/L -] = 10-12 M/L [H [OH Increasingly Acidic Increasingly Basic [OH-] = 10-4 M/L [OH-] = 10-7 M/L + [H+] > [OH-] [H ] < [OH-] Bio 230, Summer 2010, Ch 3, Page 19 14 pH Most biological solutions have a pH between 5 and 8 Buffers can help control changes in pH Calculations Calculations of pH: pH = -log10 [H+] pH Example: for 0.01 M HCl: pH = -log10 [.01] = -(-2) = 2.0 [H+] = 10 -pH 10 pH Example: for a solution at pH 2.00: [H+] = 10 -2 M = .01 M Bio 230, Summer 2010, Ch 3, Page 20 Calculations If [H+] is known, [OH-] and pOH can be calculated: [H+] [OH-] = 10 -14 M2 (Always) 10-2 x [OH-]=10 -14 M2 [OH [OH-] = 10 -12 pOH = -log10 [OH-] pH + pOH = 14 pOH = 14 - 2 = 12 Bio 230, Summer 2010, Ch 3, Page 21 ...
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