Introduction: Vinegar lab
Acids and bases (including salts that hydrolyze) behave uniquely to establish states of equilibria when they dissociate in water. There are three classic acid-base theories: Arrhenius, Bronsted-Lowry, and Lewis. The Arrhenius theory defines an acid as any substance that is capable of producing hydrogen ions (H+), or more appropriately, hydronium ions (H3O+), in aqueous solution, while a base is any substance that produces hydroxide ions in solution. According to Bronsted-Lowry theory acids by the definition are proton donors, and bases proton acceptors. Acids differ in their tendency to lose protons, and bases in tendency to accept them. Those acids that donate, and bases that accept, protons readily we call strong. Strong and weak acids and bases have different properties. This tendency is reflected by equilibrium of reaction of dissociation of acids (or bases) in water. If the equilibrium is shifted strongly to the right (concentration of H3O+ in solution is big) an acid is strong.
A titration is a procedure used in analytical chemistry to determine the amount or concentration of a substance. In a titration one reagent, the titrant, is added to another slowly. As it is added a chemical reaction occurs until one of the reagents is exhausted, and some process or device signals that this has occurred. Its purpose is generally to determine the quantity or concentration of one of the reagents, that of the other being known beforehand. In any titration there must be a rapid quantitative reaction taking place as the titrant is added, and in acid-base titrations this is a stoichiometric neutralization. The type of titration is simply the type of chemical reaction taking place, acid-base titrations.
All acid-base titration reactions are simply exchanges of protons. The reaction could be strong acid + strong base –> (neutral) salt, as in the case of HCl + NaOH –> NaCl + H2O, although the reaction would be correctly written as H3O+ + OH- –> H2O since strong acids and strong bases are totally dissociated to protons and hydroxide ions in water. For reactions which are strong acid + weak base –> (acidic) salt, such as the example HCl + CH3NH2 –> CH3NH3+Cl-, or strong base + weak acid –> (basic) salt, such as the example NaOH + CH3COOH –> Na+CH3COO+ + H2O, the cations and anions could be omitted as they do not actually act in the reaction. (Some chemists call these bystander ions.)
Mostly all acid-base titrations are carried out using a strong acid or strong base. In most cases the strong acid or strong base is used as the titrant. It is less common, but can be achievable, to place the strong acid or strong base in the titration vessel and use the weak acid or weak base as the titrant. A weak acid-weak base titration would have only a small pH change at the equivalence point. This small change is difficult to detect, and for this reason weak acid-weak base titrations are uncommon.
One of the substances involved in a titration must be used as a standard for which the amount of substance present is accurately known. The standard can be present either in the form of a pure substance or as a standard solution, which is a solution whose composition is accurately known. A standard can be prepared in only two ways: use a primary standard or standardize by titration against some previously standardized solution. A primary standard is some substance such as oxalic acid which can be precisely weighed out in pure form, so that the number of moles present can be accurately determined from the measured weight and the known molar mass.
Titration is a common method of determining the amount or concentration of an unknown substance. The method is easy to use if the quantitative relationship between two reacting solutions is known. The method is particularly well-suited to acid-base and oxidation-reduction reactions. Titrations are routinely used in industry to analyze products to be sold. In this experiment, the group will carry out a titration of vinegar with NaOH to determine the strength of vinegar and discover whether or not it is legal.
Procedure: refer to sheet
Materials: refer to sheet