Water, Acids, Bases and Buffers PDF

Water  Water Water is the most abundant substance in living systems, making up 70% or more of the weight of most organisms. Each hydrogen atom bears a partial positive charge, and the oxygen atom bears a partial negative charge.  H-Bonding...

Water  Water Water is the most abundant substance in living systems, making up 70% or more of the weight of most organisms. Each hydrogen atom bears a partial positive charge, and the oxygen atom bears a partial negative charge.  H-Bonding H-bond is the bond between an electronegative atom (the hydrogen acceptor, usually oxygen or nitrogen) and a hydrogen atom covalently bonded to another electronegative atom (the hydrogen donor) in the same or another molecule.  H-Bonding The nearly tetrahedral arrangement of the orbitals about the oxygen atom allows each water molecule to form hydrogen bonds with as many as four neighboring water molecules. Directionality of H-bonds matters H-Bonding is not unique to water  H-Bonding (weak interactions) H-bonds are comparatively weak (intermolecular interactions) than the covalent bond. Bond dissociation energy of hydrogen bond is 23 kJ/mol, compared with 470 kJ/mol for the covalent O—H bond in water. Although these four types of interactions are individually weak relative to covalent bonds, the cumulative effect of many such interactions can be very significant. Solubility of salts in water Solubility of polar molecules Polar molecules have the groups which can make H- bonds with the water.  Solubility of non-polar molecules Non-polar molecules forces energetically unfavorable changes in structure of water. Nonpolar compounds such as benzene and hexane are hydrophobic, they are unable to undergo energetically favorable interactions with water molecules, and they interfere with the hydrogen bonding among water molecules. Solubility of amphipathic molecules Micelles formation Hydrophilic portions form H-bonds with water and hydrophobic groups undergo hydrophobic interactions. Osmosis and osmolarity Isotonic Hypotonic Hypertonic  How to prevent cell bursting Plants have cell well. Monomers are present in the polymeric forms. Osmolarity depends on the number of dissolved particles, not their mass, macromolecules (proteins, nucleic acids, polysaccharides) have far less effect on the osmolarity of a solution than would an equal mass of their monomeric components. Water is essential to functions of biomolecules  Weak acids and bases Acids: Acids are defined as the species which donate proton. Strong acids: Hydrochloric, sulfuric, and nitric acids, commonly called strong acids, are completely ionized in dilute aqueous solutions; the strong bases NaOH and KOH are also completely ionized. HCl 🡪 H+ (aq)+Cl−(aq) Weak acids: The strength of these weak acids will decide when they will loose the proton.  Buffers are the mixture of weak acids & conjugate bases  Mechanism of action of acidic buffers Lets consider acetate buffer. This buffer is made up of CH3COOH (weak acid) and H3COONa (Salt of strong base). CH3COOH ⇌ CH3COO− + H+ CH3COONa 🡪 CH3COO− + Na+ Addition of a strong acid: If we add a strong acid like HCl in the solution which contain this buffer system then; HCl 🡪 H+ + Cl- So even though we are adding a strong acid which is donating its H+ in the solution but these H+ ions immediately combine with the acetate ions and produce acetic acid which is a weak acid and does not give protons as easily as HCl. The [H+] therefore remains the constant and pH remains the same as before.  Mechanism of action of acidic buffers CH3COOH ⇌ CH3COO− + H+ CH3COONa 🡪 CH3COO− + Na+ Addition of a strong base: If a strong base like (NaOH) is added to the CH3COOH/CH3COONa buffer system then; NaOH 🡪 Na+ + OH- The hydroxide ions released by the base NaOH are therefore removed as the water. The [H+] that are being used for this neutralization reaction are being constantly provided by the dissociation of CH3COOH and therefore the overall [H+] of the solution remains the same and therefore, the pH also remains the same.  Mechanism of action of basic buffers Consider a buffer system made up of NH4OH (weak base) and NH4Cl (salt of strong acid) NH4OH ⇌ NH4+ + OH- NH4Cl NH4+ + Cl- Addition of a strong acid: HCl 🡪 H+ + Cl- The hydrogen ions donated by the HCl will be removed as water. The supply of the OH- needed for this purpose is constantly provided by the ammnonium hydroxide. Thus the total [OH-] of the solution remains the constant.  Mechanism of action of basic buffers NH4OH ⇌ NH4+ + OH- NH4Cl 🡪 NH4+ + Cl- Addition of a strong base: If a strong base like (NaOH) is added to the NH4OH/NH4Cl buffer system then; NaOH 🡪 Na+ + OH- The hydroxide ions donated by the NaOH combine with NH4+ and form ammonium hydroxide (NH4OH). As the OH- are being converted to the ammonium hydroxide the overall [OH-] of the solution remains the same and thus pH remains unaffected. Phosphate buffer Bicarbonate buffer  Diabetes produces life threatening acidosis Individuals with diabetes, fasting or starvation disrupts the uptake of glucose from blood into the tissues and forces the tissues to use stored fatty acids as their primary fuel. Metabolism shift to the fatty acids. Fatty acid utilization produces ketone bodies, β-hydroxybutyric acid and acetoacetic acid, which drop the pH of plasma.