Gujarat BoardEnglish MediumSTD 12 ScienceChemistryAlcohols, Phenols, and Ethers2 Marks
Question
Explain a process in which a biocatalyst is used in industrial preparation of a compound known to you.
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Answer
Biocatalysts are complex organic compounds which act as catalysts in reaction taking place in living organism. These biocatalysts (enzymes) are used in the manufacture of ethanol. Ethanol from sugar solution (molasses):
Molasses is a non-crystalline form of sugar obtained as the mother liquor after crystallisation of sugar from sugar solution. This contains about $50\%$ sugar. It is diluted to about $10\%$ solution and yeast is added and kept for about $2-3$ days. Yeast supplies the enzymes invertase and zymase. The enzyme invertase hydrolyses sucrose to glucose and fructose. The enzyme zymase (found in yeast) converts glucose and fructose to ethanol.
$\text{C}_{12}\text{H}_{22}\text{O}_\text{11}+\text{H}_2\text{O}\xrightarrow{\text{Invertase}}\text{C}_6\text{H}_{12}\text{O}_6+\text{C}_6\text{H}_{12}\text{O}_6 \\ \ \ \text{Sucrose} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Glucose} \ \ \ \ \ \ \text{Fructose}$
$\ \ \ \ \ \ \ \ \ \ \text{C}_6\text{H}_{12}\text{O}_6 \ \ \ \ \ \ \ \xrightarrow{\text{Zymase}} \ \ \ \ \ \ \ 2\text{C}_2\text{H}_5\text{OH} \ \ \ \ \ \ + \ \ \ \ \ \ 2\text{CO}_2\\ \text{Glucose or fructose } \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Ethanol}$
In wine making, grapes are the source of sugars and yeast. As grapes ripen, the quantity of sugar increases and the yeast grows on the skin of the grapes. When the grapes are crushed, sugar and enzyme come in contact and fermentation starts. Fermentation takes place under anaerobic conditions (i.e., in the absence of air). During fermentation $CO_2$ is released.
The action of enzyme is inhibited when the concentration of alcohol exceeds $14\%.$ If air enters the fermentation mixture, the $O_2$ of the air oxidised ethanol to ethanoic acid which spoils the taste of alcoholic drinks and makes it sour.
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