MediumChemistryHigh School (11–12)Organic Compounds with Functional GroupsNumerical

A hexose (molar mass 180.16 g/mol) is treated with excess acetic anhydride…

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A hexose (molar mass $180.16\ \text{g/mol}$ ) is treated with excess acetic anhydride. A sample of $1.80\ \text{g}$ of the sugar gives $3.90\ \text{g}$ of the acetylated product, with every reactive $\text{-}\text{OH}$ group changed to $\text{-}\text{OCOCH}_{3}$ . Each change replaces an H atom by a $\text{COCH}_{3}$ group and adds $42.04\ \text{g/mol}$ . Find how many $\text{-}\text{OH}$ groups the sugar has.

Need a reminder? The key ideaShow

A carbohydrate is a polyhydroxy aldehyde or ketone. An aldose has $n - 2$ stereocentres and a ketose has $n - 3$ , where $n$ is the number of carbons in the chain. The number of stereoisomers is $2^{\text{centres}}$ , and half of them belong to the D series. An empirical formula comes from the moles of each element in 100 g.

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.

← All Problems

← A sugar of molar mass 150 g/mol contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass…A student dissolves 2.50 g of pure α-D-glucose in water to make 25.0 mL of solution… →

More onOrganic Compounds with Functional Groups

Discussion (0)

Loading…