A sample of 8.10 g of starch is hydrolysed completely to glucose…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A sample of of starch is hydrolysed completely to glucose. The molar mass of one glucose unit in starch is and that of glucose is . The glucose is then fermented with yeast: . Take ethanol as and the molar volume of a gas as . Find the mass of glucose, the mass of ethanol, and the volume of carbon dioxide, assuming complete conversion.
Need a reminder? The key ideaShow
A glycosidic link releases one molecule of water, so units in a chain have links. Hydrolysis adds the water back. Sucrose gives equal moles of glucose and fructose. The observed rotation of a mixture is the sum of the contributions of each sugar: .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Moles of glucose units, then moles of glucose, then the products.
Step 1. Moles. of units, which gives the same amount of glucose.
Step 2. Glucose. .
Step 3. Ethanol. , and .
Step 4. Carbon dioxide. .
Answer: of glucose, of ethanol and of carbon dioxide.
Check. The glucose is of the starch, as .
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