Examine the pKa values for the organic acids found in wine. Now examine the titr
ID: 510905 • Letter: E
Question
Examine the pKa values for the organic acids found in wine. Now examine the titration curves (i, e. Solution pH vs mL titrant) applicable to weak acids. What do you think is the initial pH for wine in D.I. water? 2 7 3 6 Which of the following is NOT true regarding the value for pKa based on a titration curve using a pH electrode to determine the equivalence point? pKa =pH at the first inflection point (i.e. point where slope changes sign) on the titration curve pKa =pH at 1/2 the volume of the equivalence point pKa= pH at the equivalence point pKa for polyprotic acid=pH at 1/2 the volume of the equivalence point and represents the average response of all the acidic protons (ie. different pKa values)Explanation / Answer
Answer of Q. No :7 : Initial pH of Win in DI water will be nearly 6.0. the discription is as follows,
1.Monitoring of organic acids in wine is very important for the processes control during alcoholic and malolactic
fermentation and for the wine quality. Organic acids have influence on the organoleptic properties and stability
of wine. Some of the organic acids originate from the grapes (tartaric, malic, citric and shikimic) and some of
them as lactic and succinic acids are products of alcoholic and malolactic fermentation.
2. Solutions (such as wine) can have a pH in the range 0 to 14. A pH of 0 represents a strong acid solution, while a pH of
14 represents a strong alkaline solution. Distilled water has a theoretical pH of 7, and wines are in the range of 3 to 4.
More specifically, the pH level of musts and wines should be within the following recommended ranges for a desired style of wine.
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The answer of Que no 12 : pH = pka at first inflation poit is not true
Titrations are often recorded on graphs called titration curves, which generally contain the volume of the titrant as the independent variable and the pH of the solution as the dependent variable (because it changes depending on the composition of the two solutions).
The equivalence point is where all of the starting solution (usually an acid) has been neutralized by the titrant (usually a base). It can be calculated precisely by finding the second derivative of the titration curve and computing the points of inflection (where the graph changes concavity); however, in most cases, simple visual inspection of the curve will suffice. To calculate the acid dissociation constant (pKa), one must find the volume at the half-equivalence point, that is where half the amount of titrant has been added to form the next compound.
Therefore, the Henderson-Hasselbalch equation can give the proper answer
pH= pKa+ log (base/acid)
pH= pKa + log(1)
pH = pKa
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