[jgaoxx06]

Hi everyone,

I'm doing A-level Chemistry Nuffield papers, and I've come across a question about hydroxylamine NH2OH.
The first part says

"Hydroxylamine can be thought of as being derived from ammonia NH3, by the replacement of one hydrogen atom by a hydroxyl, OH, group."

Then it asks to "Draw a 'dot-and-cross' diagram for hydroxylamine, and predict the bond angles", so I've done that, and I think the bond angles are HNH-107 NOH-104.5.

Then it says "What would you expect the pH of an aqueous solution of hydroxylamine to be? Justify your answer and write an equation for the equilibrium reaction between water and hydroxylamine."

Now, for the exam, we are allowed our databooks, so I've looked at the reaction of hydroxylamine with water, found out the pH and equation, but how would you know if something is a strong or weak base without working out the dissociation constant? Is it to do with the attraction of nitrogen atoms to the OH groups? Maybe the attraction between nitrogen and the hydroxyl group is strong, so it will hardly dissociate? But isn't the electron-attracting power of NH2 weaker than the groups Cl, OH and OCH3?

[Albert]

Then it says "What would you expect the pH of an aqueous solution of hydroxylamine to be? Justify your answer and write an equation for the equilibrium reaction between water and hydroxylamine."

Now, for the exam, we are allowed our databooks, so I've looked at the reaction of hydroxylamine with water, found out the pH and equation, but how would you know if something is a strong or weak base without working out the dissociation constant? Is it to do with the attraction of nitrogen atoms to the OH groups? Maybe the attraction between nitrogen and the hydroxyl group is strong, so it will hardly dissociate? But isn't the electron-attracting power of NH2 weaker than the groups Cl, OH and OCH3?

I think the question is just about whether the pH is above, below or equal to 7.

[jgaoxx06]

But it says to "justify your answer", how could I do that?

[Albert]

I'd just answer:

NH₂OH + H₂O <=> NH₃OH⁺ + OH^-

...but I'd also like to know someone else's opinion about this matter.

[AWK]

Hydroxylamine is basic, the question is whether it is more basic or less basic then ammonia , and explanation of this  property.

[webqc.org]

Hydroxylamine is basic, the question is whether it is more basic or less basic then ammonia , and explanation of this  property.

It sould be less basic than ammonia, since we've replaced -H with electronegative -OH.
And in fact it is less basic: Kb(HONH2)=1.1e-8 vs. Kb(NH3)=1.8e-5