The definition my science booklet has for a base is a substance with an OH- ion. I told my teacher that I thought the definition in the book might have had limitations and he basically made me feel like a complete idiot. However, I thought ammonia was basic but NH3 doesn't have OH. I probably am wrong here, but could someone please explain to me why I'm wrong because I'm really confused. Is it only a base in solution or something? Because I thought it could react in gaseous form and operate as a base. As I'm fairly certain it's quite obvious, I don't really know a whole lot, so a little help and an explanation as to what I have done wrong would be really helpful. Thank you

The definition my science booklet has for a base is a substance with an OH- ion. I told my teacher that I thought the definition in the book might have had limitations and he basically made me feel like a complete idiot. However, I thought ammonia was basic but NH3 doesn't have OH. I probably am wrong here, but could someone please explain to me why I'm wrong because I'm really confused. Is it only a base in solution or something? Because I thought it could react in gaseous form and operate as a base. As I'm fairly certain it's quite obvious, I don't really know a whole lot, so a little help and an explanation as to what I have done wrong would be really helpful. Thank you

 

The are multiple definitions of a base. Only one definition of a base (Arrhenius) states that it must produce OH- ions upon dissolving in water. This only applies to aqueous solutions (or solutes dissolved in solvents that are polar), so it will not work for products not dissolved in water.

 

Gaseous ammonia fits in two other definitions for a base, though. The Bronsted Lowry definition of a base states that a base is a proton acceptor. Ammonia (NH3) accepts a proton from an acid (gaseous HCl) to form ammonium ions (NH4+), thus making it a Bronsted-Lowry base. Gaseous ammonia is also a Lewis base, donating a pair of electrons to a proton (in acids), also making the ammonium ion. So yes, gaseous ammonia is a base.

You are absolutely correct to say that it has limitations and honestly, your teacher is an idiot if he made you feel that you were wrong for suggesting it. The Arrhenius definition for acids and bases (which is what you've described) is very outdated and these days, only ever mentioned to give context to the Bronsted-Lowry model (described by weiming).

Thank-you both so much, a lot less confused now!