Final answer:
A Tollen's test can be used to show that but-2-enal is an aldehyde; a positive result is indicated by the formation of a silver mirror inside the test tube.
Step-by-step explanation:
To determine if but-2-enal is an aldehyde, a simple and reliable chemical test is the Tollen's test. This test uses Tollen's reagent ([Ag(NH3)2]OH), which reacts with aldehydes to produce a noticeable silver mirror on the inner walls of the test tube.
When the reagent is mixed with but-2-enal, if it is indeed an aldehyde, the oxidation reaction will take place and the silver mirror will form, indicating a positive result for an aldehyde. In contrast, ketones do not react to produce such a change with Tollen's reagent.
To show that but-2-enal is an aldehyde, you can use Tollens' test for aldehydes. In this test, Tollens' reagent (a solution of silver nitrate in ammonia) is mixed with the sample. Aldehydes are easily oxidized and react with Tollens' reagent to produce a silver mirror. Ketones, on the other hand, do not react with Tollens' reagent.
For example, if you mix Tollens' reagent with but-2-enal, you will observe a silver mirror formation, indicating the presence of an aldehyde group.