Carbonyl compounds: describe question

A student oxidises ethanol to ethanal using acidified potassium dichromate(VI). The reaction mixture is heated and the product is collected by distillation.

Describe the essential practical conditions needed to obtain ethanal as the main organic product, and explain why heating under reflux would change the outcome. In your answer, include the reagents, the colour change observed, and a chemical test that could be used to confirm that the product is an aldehyde rather than a ketone.