To determine the concentration of a given acid by its titration against alkali.
An acid is a substance that increases the concentration of H 3 O + (hydronium ion) in aqueous solution. A base: is a substance that decreases the concentration of H 3 O + in aqueous solution. A decrease in [H 3 O + ] requires an increase in [OH - ], so we can define the base as a substance that increase the concentration of OH - in aqueous solution. H + is called a proton, because a proton is all that remains when a hydrogen atom loses its electron. Hydronium ion (H 3 O + ) is a combination of H + with H 2 O.
Bronsted and Lowry definition of acids and bases An acid is a proton donor A base is a proton acceptor. Example HCl is an acid because it donates a proton to H 2 O to form H 3 O + HCl (l) + H 2 O H 3 O + (aq) + Cl - (aq) Salts: - Any ionic solid such as ammonium chloride is called salt. It can be thought of as the product of an acid base reaction. - Most salts are strong electrolytes, i.e. they dissociate almost completely into their component ions when dissolved in water NH 4 + Cl - NH 4 + + Cl -
A standard solution (standard titrant) is a reagent of known concentration that is used to carry out a titrimetric analysis Titration: is a procedure performed by adding a standard solution from a buret or other liquid-dispensing devices to a solution of the analyte until the reaction between the two is judged complete. Equivalence point in titration is reached when the amount of added titrant is chemically equivalent to the amount of analyte in the sample E.g. AgNO 3 + Cl - AgCl mol mol (Equivalent points can ’ t be determined experimentally) End point is the point in a titration when physical change occurs that is associated with the condition of chemical equivalence. Indicator: a chemical compound that change it ’ s color or other physical property at or near the equivalence point.