dat destroyer gen chem problem #1

[jz123]

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For #1 in destroyer, the Kb value was 1.1*10^-8.
It is obvious that amines are basic, however, this given Kb value brings me some confusion.

So we know that water has a Kb water of 1*10^-7, which is larger than the given Kb for hydroxyl amine. Doesn't this mean water is relatively more basic than hydroxyl amine in this case? So wouldn't water act as a base and the hydroxyl amine acts as an acid? Please clarify. Thanks.

 

[DAT Destroyer]

For #1 in destroyer, the Kb value was 1.1*10^-8.
It is obvious that amines are basic, however, this given Kb value brings me some confusion.

So we know that water has a Kb water of 1*10^-7, which is larger than the given Kb for hydroxyl amine. Doesn't this mean water is relatively more basic than hydroxyl amine in this case? So wouldn't water act as a base and the hydroxyl amine acts as an acid? Please clarify. Thanks.

Whoa Whoa Whoa,,,,,,the value of the water constant is called the Kw, and is 1x 10 exp -14......You are thinking of the hydroxide ion concentration. The amine is more basic than water.....Let me prove it to you. Lets us PROTONATE both water and the amine and examine the conjugate acids. Water once protonated, water..... actually H30+... has a Ka of about -2.....while the protonated amine about 9. That is a 1x10 exp 11 difference !!!!! Since the protonated water...actually called hydronium is the stronger acid, it will be the weaker base. This is a great way to decide strength if you are undecided. In this problem, I wanted to test the understanding that an amine is a base, and as such...it will accept a proton. This is a very important question that you may see one day !!!!

Hope this helps

Dr. Romano

 

[jz123]

Whoa Whoa Whoa,,,,,,the value of the water constant is called the Kw, and is 1x 10 exp -14......You are thinking of the hydroxide ion concentration. The amine is more basic than water.....Let me prove it to you. Lets us PROTONATE both water and the amine and examine the conjugate acids. Water once protonated, water..... actually H30+... has a Ka of about -2.....while the protonated amine about 9. That is a 1x10 exp 11 difference !!!!! Since the protonated water...actually called hydronium is the stronger acid, it will be the weaker base. This is a great way to decide strength if you are undecided. In this problem, I wanted to test the understanding that an amine is a base, and as such...it will accept a proton. This is a very important question that you may see one day !!!!

Hope this helps

Dr. Romano

Thanks for the explanation. It helps.