Objective
There are three objectives for the alkalinity and hardness experiment. First, the experiment aims at conducting a titration between a strong acid and a weak base. Secondly, the experiment aims at perceiving the alkalinity concept. Finally, the experiment also aims at investigating the hardness of water samples.
Theory
The quantitative capacity of a water sample to neutralize an acid is referred to as alkalinity. According to American Water Works Association (Hargesheimer et al. 110), the major causes of alkalinity are carbonate concentrations (〖Ca〗_3^(2-)), bicarbonate concentrations (〖HCO〗_3^-), and hydroxide concentrations (〖OH〗^-). Alkalinity is highly significant in drinking water industry due to its pH buffering capabilities, where it is expressed as milligrams per liter of calcium carbonate (〖CaCO〗_3) (Hargesheimer et al. 110). In this particular experiment, 0.02N H_2 〖SO〗_4 is used to titrate different water samples through volumetric titration.
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"Alkalinity and Hardness".
The presence of polyvalent metallic cations in water causes hardness in water, where it is expressed as milligrams per liter of calcium carbonate (〖CaCO〗_3). The ions 〖Ca〗^(2+)and 〖Mg〗^(2+)are primarily involved in the hardness of water through the presence of a chelating agent such as ethylenediamine or ethylenediaminetetraacetic acid (EDTA). Suppose EDTA is chosen as chelating agent, then the reaction with the magnesium nd calcium ions will be;
〖Mg〗^(2+)+EDTA→〖[Mg*EDTA]〗_complex
and
〖Ca〗^(2+)+EDTA→〖[Ca*EDTA]〗_complex
A color indicator is required to indicate the acid-base reaction. In this case, Eriochrome Black T (EBT) is used as the indicator where complexes are formed as;
〖Mg〗^(2+)+EBT→〖[Mg*EBT]〗_complex
And
〖Ca〗^(2+)+EBT→〖[Ca*EBT]〗_complex
The EBT is initially added in the water sample which changes the color of the ions to wine-red as the 〖Ca〗^(2+)and 〖Mg〗^(2+) complexes develop. As the titration begins, the addition of the EDTA breaks the Mg*EBT and Ca*EBT complexes by pulling the 〖Ca〗^(2+)and 〖Mg〗^(2+) ions from the weak EBT complexes to former stronger Mg*EDTA and Ca*EDTA complexes. The titration reaches endpoint when EDTA successfully pulls away all the 〖Ca〗^(2+)and 〖Mg〗^(2+) ions from the Mg*EBT and Ca*EBT complexes which gives a blue colored solution. Although the titration of an alkaline with EDTA yields successful and certain results, the integrity of the results can be compromised by various interferences. In such situations, the experiment is modified in various ways.
