[Zwrei]

What are their structure/equation when reacted with Sodium hydroxide (NaOH)
1. Formaldehyde  with  40% NaOH
2. benzaldehyde  with  40% NaOH
3. acetaldehyde  with  40% NaOH
4. acetaldehyde  with  10% NaOH
5. acetone  with  10% NaOH

[Arkcon]

Can you work with some of the information is this tread:  http://www.chemicalforums.com/index.php?topic=46051.msg198936#msg198936  in order to begin to come up with an answer of your own?

[Zwrei]

Formaldehyde reacts with 40% NaOH = Observation: It gives foul smell
Benzaldehyde reacts with 40% NaOH = Observation: White precipitate w/ oily layer, smells like alcohol
Acetaldehyde reacts with 40% NaOH = Observation: Dark orange precipitate, cinnamon smell
Acetaldehyde reacts with 10% NaOH = Observation: Dark orange liquid
Acetone reacts with 10% NaOH = Observation Colorless Liquid

Can someone explain the observations? How did it get that color and smell.

[Zwrei]

I mean their general structure like

Formaldehyde

2HCHO + NaOH → HCOONa + CH3OH

[discodermolide]

I mean their general structure like

Formaldehyde

2HCHO + NaOH → HCOONa + CH3OH

As I said before look up the Canizzaro reaction and the aldol reaction.

[Arkcon]

Here's a Wikipedia link (it removes a slight typo):  http://en.wikipedia.org/wiki/Cannizzaro_reaction  Zwrei: can you work with that general equation, and apply it to your question?

[fledarmus]

This may be going a little too far with hints, but one of the two reactions mentioned for your consideration by previous respondents will only work when there are alpha hydrogens (hydrogens on carbons adjacent to the carbonyl). The other, typically much slower reactions, only has a chance to predominate when there are no alpha hydrogens. This, combined with the structures of your starting materials, should give you a fairly good place to start identifying your products.