University:
Kentucky State University
Course:
CHE 315 | Biochemistry
Academic year:

2024
Views:

80

Pages:

18
Author:

MoGhoadoAnotozj14

Titration Titration is an experiment in which measured amounts of base are added to a measured amount of acid while following up changes in pH using a pH meter. 51 Titration Curves and Buffers CH3COOH + OHIn the region small pH changes upon addition of acid or base, the acid/base ratio varies within a narrow range The point in the titration at which the acid is exactly neutralized is called the equivalence point. CH3COO- + H2O [HA] > [A-] [HA] < [A-] pH = pKa [CH3COOH] = [CH3COO-] Inflection point Significant changes in pH are harmful, ex. disruption of DNA double helix, disruption of protein structure, etc… Buffers are solutions that resist abrupt and sudden changes in pH. 52 Buffering capacity The buffer capacity is the amount of acid or base that can be added to a buffer solution before a significant change in pH occurs Buffering Capacity depends on: 1. Buffer concentration 2. pKa of the buffer 3. The desired pH 53 How do we choose buffers? 1. Suitable pKa for the buffer. pKa ±1 pH unit from the pH of the reaction pKa ±½ pH unit is even better 2. No interference with the reaction. 3. Suitable buffering capacity. 4. No precipitation of reactants or products due to presence of the buffer. 5. Nonbiological nature of the buffer. Examples of biochemical buffers include HEPES, PIPES and TRIS 54 Buffer Calculations Example: A buffer consists of 0.2 mole CH3COO- in 500 ml of 0.1 M CH3COOH. ( Ka = 1.8 x10-6 M). What is the PH? Ka = [H+] x 0.4 / 0.1=1.8 x 10-6 [H+] = 4.5 x 10-6 M PH = - log 4.5x 10-6 = 5.4 55 Buffer Calculations Calculate the mass of sod. propionate to be dissolved in 1L of 1M propionic acid ( M.W = 96.08 gr/mole) to give a buffer of PH=4.5 (pKa = 4.87) pH = 4.5 [H+]= 10-4.5 pKa = 4.87 Ka= 10-4.87 Ka = [H+] [propionate] ∕ [propionic acid] [propionate] = 1 x 10 -4.87 ∕ 10-4.5 = 0.427 M Mass= 0.427x 96.08 = 41.0 gr 56 pH in the body -Blood pH is between 7.36 and 7.44 -Intracellular pH is between 6.9 and 7.4 - When pH< 7.36, acidosis results. pH<7.25 life threatening -Acidosis causes CNS depression and coma -pH<7 death occurs. 57 Acidosis -Metabolic acidosis: Starvation, untreated diabetes, high-protein diet, high-fat diet -Respiratory acidosis 58 Alkalosis -pH> 7.44 -pH>7.55 is dangerous and >7.60 results in death. -Metabolic alkalosis: Excess clinical administration of salts and metabolic acids as Na lactate and NaHCO3 Deamination of amino acids, citrate Severe vomiting -Respiratory alkalosis : Hyperventilation (heavy breathing) Hysteria, anxiety or altitude sickness 59 Buffer systems in the body 1.The bicarbonate–carbonic acid buffer system (ECF) 2.The hemoglobin buffer system in RBCs 3.The phosphate buffer system in all types of cells 4.The protein buffer system of cells and plasma. -Buffers act quickly but not permanently -Buffers do not remove acids or replenish alkali in the body 60 The bicarbonate–carbonic acid buffer system in blood CO2(g) CO2(aq) CO2(aq) + H2O(l) H2CO3(aq) Net: CO2(g) + H2O(l) H2CO3(aq) H+(aq) + HCO3-(aq) H+(aq) + HCO3-(aq) 61 The bicarbonate–carbonic acid buffer system in blood CO2(g) + H2O(l) H+(aq) + HCO3-(aq) [HCO3-] / [CO2] = 25 mM/ 1.25 m M = 20 most of the dissolved CO2 is present as HCO3- Buffer range = 6.1 + 1 = 5.1-7.1 Normal values: pH = 7.4 pCO2 = 40 mm Hg (~ 1.2 mM) [HCO3-] = 25 mM 62 What happens when the pH of the blood drops? - Low pH means more H+ H+(aq) + HCO3-(aq) H2CO3(aq) CO2(aq) H2CO3(aq) CO2 CO2(aq) + H2O(l) CO2(g) exhaled by the lungs -Aspirin -High altitudes - rate of respiration increases. 63 What happens when the pH of the blood increases? - Higher pH means more OHNaOH + H2CO3 NaHCO3 + H2O CO2 + H2O consumed acid H2CO3 to replace the [CO2] decrease and respiration decrease to reduce the rate of CO2 consumption. 64 Protein Buffers -Because of the presence of the dissociable acidic (-COOH) and basic (-NH2) groups, proteins act as buffers. -Particularly the imidazole group of the side chain of histidine residue (pKa = 7.3) Proteins, specifically Albumin, account for 95% of non-carbonate buffering action in plasma (has 16 His/mole) Histidine 65 Phosphate Buffer systems -Phosphate anions and proteins are important buffers that maintain a constant pH of ICF. -Intracellular and tubular fluids of kidney - H2PO4- dissociates to H + and HPO4-2 -pKa is 7.1-7.2 66 Hemoglobin (Hb) Buffer -Major intracellular buffer of the blood -Hb has a high number of His (38 molecules/mole of Hb) -Works cooperatively with the bicarbonate buffer system 67 Buffer systems of the body 68

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