: 220
Titration determines unknown concentration by reacting with a standard solution. At equivalence: meq(titrant) = meq(analyte). N1V1 = N2V2 or M1V1n1 = M2V2n2. Acid-base titrations: strong acid + strong base: any indicator. Weak acid + strong base: phenolphthalein (endpoint pH > 7). Strong acid + weak base: methyl orange (endpoint pH < 7). Redox titrations: KMnO4 is self-indicator (purple to colourless in acid). Iodometric: I2 with Na2S2O3 using starch indicator (blue to colourless). K2Cr2O7 with diphenylamine indicator. Back titration: add excess reagent, titrate unreacted portion. meq(analyte) = meq(added) - meq(unreacted). Used for: insoluble samples, slow reactions, unclear endpoints. Double titration: NaOH + Na2CO3 + HCl. Phenolphthalein endpoint (V1): neutralises all NaOH + half Na2CO3. Methyl orange endpoint (additional V2): neutralises remaining NaHCO3. meq NaOH = N(V1 - V2). meq Na2CO3 = 2NV2. If V1 > V2: NaOH + Na2CO3 mixture. If V1 < V2: Na2CO3 + NaHCO3 mixture. If V1 = V2: pure Na2CO3.