A student dissolves 2.50 g of pure α-D-glucose in water to make 25.0 mL of solution…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student dissolves of pure α-D-glucose in water to make of solution. She puts it in a polarimeter tube long and reads the rotation at once. The specific rotation of pure α-D-glucose is degrees. A day later the solution is at equilibrium, with a specific rotation of degrees. Find the concentration, the first reading and the final reading.
Need a reminder? The key ideaShow
The anomeric carbon is C-1 of an aldose. A group on the right of the Fischer projection points down in the Haworth ring and a group on the left points up. In a D sugar, the anomeric of the α form points down and that of the β form points up. The specific rotation is , with in dm and in g/mL.
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.
Given. , , .
Step 1. Concentration. .
Step 2. First reading. degrees.
Step 3. Final reading. degrees.
Answer: , degrees and degrees.
Check. The reading falls because the β form, with a smaller rotation, forms until the equilibrium mixture is reached.
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