Question

The correct answer is the 3rd one.

NO3- has more charges and thus is more unstable than water, so wouldn't it be more likely for it to accept H+, making it a stronger Bronsted-Lowry base compared to H20? (aka, Why is water better at accepting H+ than NO3-?)

F- should be the strongest Bronsted-lowry base because HF is a weak acid and thus its CB is more unstable (that's why it doens't really want to donate its H+) -> an unstable Conjugate Base would make it most likely to accept H+, which is a definition of a strong Bronsted Lowry base. Is my reasoning as to why F- is the strongest Bronsted Lowry base correct?

Question 2 0.17 pts From the following chemical reactions determine the relative Bronsted-Lowry base strengths (strongest to weakest). HNO3(aq) + H2O(l) → H30+(aq) + NO3- (aq) HF(aq) + H2O(1) <===> H30+(aq) + F"(aq) HNO3 > H30+ > HF O NO3> H20>F OF > H2O > NO3 OF > NO3> H20

Answer 1

According to Bronsted-Lowry acid base principle, the species that donates a proton is an acid and the species that accepts a proton is a base.

Hence, in the first reaction

HNO3(aq) + H200 → H30 Tag) + NO3(aq)

HNO3(aq) : acid

H2O: base

H30+ : conjugate acid of H2O

NO3 : conjugate base of HNO3

Now, another principle at work here is the more stable the conjugate base of an acid, the more likely is the acid to donate a proton as that will lead to the formation of the stable conjugate base and thus making the acid a strong acid.

If the conjugate base is stable, it does not want to lose its stability by accepting a proton, and thereby behaves as a weak base.

Hence, a stronger acid forms a weaker conjugate base and vice versa.

Now, looking at the first reaction, the equilibrium is completely towards the products as evident by the right reaction arrow. Hence, the conjugate base $NO_3^-$ must be very stable and thus a very weak base. This makes sense as HNO3 readily gives away a proton to the water molecule. Hence, water must be a stronger base than NO3-.

The stability of NO3- as a conjugate base is because of the following:

NO; is stable as its two negative charges are distributed between the three O atoms via resonance structures shown below. O +2- OSZ o

Now, lets take a look at the second equation

HF(aq) + H2O(1) = H30 ) + Flag

Here notice that the arrow is a double headed equilibrium arrow which means the reverse reaction is also happening unlike the first equation above.

Here HF is donating a proton to water by forming a conjugate base $F^-.$

F- is not very stable as it has a very high electron density on F atom because of the negative charge on F and its small size.

Hence, F- readily gets protonated by the conjugate acid of water to form HF in the reverse reaction. It means F- is a stronger base than H2O.

Hence, its conjugate base water must be weaker than the conjugate base of HF.

Hence, the order of base strength will be

F-> H2O > No

Note: your reasoning is somewhat correct for the second part. For the first part you need to say why NO3- is stable by showing the resonance forms. Main hint in the question is in the arrow between reactant and product. The arrows towards the product indicates products are very stable compared to reactants in first reaction. The equilibrium arrow indicates that both the reactant and products are not very stable and exist in equilibrium with each other leading to our conclusions.