Hey everyone. So here it says without using pKa values, which of the following pairs is more acidic? Let's look at the first option. Here we have ammonia versus hydrosulfuric acid. Alright. We have H connected to nitrogen, and H connected to sulfur. Here we're going to try to figure out what type of technique we could use to determine which one is more acidic. Alright. In this case, we can rely on the element effect. If we look at our periodic table, we can see that nitrogen is in Group 5A. Sulfur is in Group 6A. But Sulfur is not in the same row as Nitrogen; it's one lower.
If we look at their electronegativities, although sulfur is more to the right than nitrogen, sulfur is not more electronegative. Sulfur, being lowered down, decreases your electronegative values. Nitrogen is just slightly more electronegative. But here the deciding factor in terms of the element effect is that Sulfur is larger in size. Remember, the trend is as we head towards the right side of the periodic table, our atomic radius or atomic size is going to decrease. But as you go down a group, it's going to increase. Sulfur being larger than nitrogen means that sulfur would be more acidic. Its bonds will be longer, and it'd be easier for us to remove an H+ from the sulfur atom. So here, SH2 would be more acidic than NH3. Again, it's based on our Element Effect or atomic size.
If we want to verify this, I know the question says without using pKa values, but we've decided on what our answer is. If we looked up the pKa values, you would see that NH3 has a pKa value of about 38. And Hydrosulfuric acid here has a pKa of around 10. It has a lower pKa value, which means it's more acidic. So here, Hydrosulfuric acid will be the more acidic of the pair, and it's based on the element effect or atomic size of sulfur versus nitrogen. Sulfur being larger means it's more acidic overall. Alright. Let's just use that one for this particular pair and continue with the other ones to see what the pairs will be for those.