Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
of ethanal () is used in two separate experiments. In the first, all of it is warmed with excess Tollens' reagent. In the second, the same mass is warmed with excess Fehling's solution. Tollens' reagent gives mol of silver () for each mole of aldehyde. Fehling's solution gives mol of copper(I) oxide (). Find the amount of ethanal in the sample. Then find the mass of silver from the first experiment, and the mass of copper(I) oxide from the second.
NaBH, LiAlH and H with a metal reduce C=O to an alcohol. Zn-Hg with conc. HCl (Clemmensen) or NHNH then KOH (Wolff-Kishner) reduce it to CH. Tollens' reagent gives 2 Ag for each aldehyde group, and Fehling's solution gives 1 CuO. The iodoform test is given by CHCO- groups and CHCH(OH)- groups.
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.
Step 1. .
Step 2. Silver. .
Step 3. Copper(I) oxide. .
Answer: , of silver and of copper(I) oxide.
Watch out. Methanal would give four silver atoms for each molecule, not two, because methanoic acid is oxidised on.
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