AAMC9: Why is this solution basic?

[sudo]

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I just retook AAMC 9 PS, and this is the only question I got wrong, so it's obviously something I don't understand...

Can someone please explain the reasoning behind it? The explanation wasn't very helpful to me 🙁

Thank you

 

[pm1]

so when NaNO2 is in solution it breaks down into its ions. Na+ and NO2-
NO2- being a base will pull out a H+ from water, forming OH-, consequently increasing the pH.

let me know if that makes sense.

 

[sudo]

so when NaNO2 is in solution it breaks down into its ions. Na+ and NO2-
NO2- being a base will pull out a H+ from water, forming OH-, consequently increasing the pH.

let me know if that makes sense.

Thank you, again 🙂 Makes sense. NO2- is a lewis base (because of it's two lone pairs), right?

 

[grapepopsicle]

Let's look at the other answer choices:
B) Na+ will pretty much do nothing in aqueous solution; it won't react with anything. Alkali metal cations are pretty much all completely soluble and inert in water. Even if it did react with something, it would react with OH-, which would make the solution more acidic.
C) and D) you can't change the Ka of a reaction by adding one of the reactants/products. You can only change the equilibrium constant by changing the temperature. So these are obviously wrong.

Like pm1 was saying: nitrous acid is a weak acid, so the conjugate base, nitrite, will react (to a small degree) with the H+ that come from the autoionization of water. This decreases H+ concentration and makes the solution more basic. (OH- concentration increases because the H+ it ionized with (from water) has reacted with the nitrite.)

 

[pm1]

Thank you, again 🙂 Makes sense. NO2- is a lewis base (because of it's two lone pairs), right?

yes, lewis base - electron pair donator, it is also a bronsted-lowry (not sure about the spelling) base because it is a proton acceptor.
As grapepopsicle put it, the passage says that HNO2 is a weak acid, so you can assume NO2- is its conjugate base.