Acid-Base Chemistry Lab Essay

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The purpose of this lab was to determine the pH and total acidity of grape juice and wine. A second purpose was to experimentally determine the pKa of a monoprotic weak acid, polyprotic weak acid, as well as, a free amino acid, alanine.

Acids and bases were defined by Bronsted-Lowry in 1923, in which acids were described as substances capable of donating a proton and bases are substances capable of accepting a proton (Thompson and Dinh 2009). In addition to defining acids and bases, Bronsted-Lowry further classified acids and bases as being either strong or weak. By definition, a strong acid or base is a substance that is completely dissociated in aqueous solutions and in contrast, weak acids only partially
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Once all reducing sugars are fermented to ethanol, yeast levels begin to decline and lactic acid bacteria are able to grow.
Alcoholic fermentation is followed by malolactic fermentation (MLF), which is a current method wine makers utilize to reduce wine acidity and to obtain microbial stability in wine (Husnik and others 2006; Ugliano and Moio 2005; Lonvaud-Funel 1999). L-malic and L-tartaric are the two main organic acids found in grape musts (Husnik and others 2006). The purpose of MLF is to transform L-malic acid into L-lactic acid, with the release of carbon dioxide. The decarboxylation of L-malic acid to L-lactic acid is usually conducted by lactic acid bacteria genera, such as Oenococcus, Pediococcus, or Lactobacillus (Ugliano and Moio 2005). Once all malic acid is degraded, lactic acid bacteria must be eliminated by sulfiting (Lonvaud-Funel 1999). Sugar and alcohol content are two basic, yet important quality factors of wines (Son and others 2009). Sugar and alcohol concentrations are vital components of wine that must be carefully monitored during the entire fermentation process. Common methods for determining alcohol concentration are: measuring boiling point, distillation and specific gravity, chemical oxidation, and gas-chromotography (Son and others 2009). As outlined by Son and others (2009), the soluble solids portion of wine,
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