Sorry to post again but I'm really stuck on this one!

I'm doing some post lab questions and I'm stuck on one. In lab we performed Tollens test, Fehlings test, and Jones Oxidation to differentiate our unknown between an aldehyde or a ketone. The question I'm stuck on is " older bottles of benzaldehyde are often contaminated with benzoic acid. Would this affect the tests carried out in the lab if you had a sample from a contaminated bottle? If so, how would it change the results?" Any help or hints?