You can see that hydroxide ion is a stronger base than ammonia (NH3), because ammonium (NH4+, pKa = 9.2) is a stronger acid than water (pKa = 14.00). What this means, you may recall, is that the negative charge on the acetate ion is not located on one oxygen or the other: rather it is shared between the two. The best answers are voted up and rise to the top, Not the answer you're looking for? This effect is most important when there is another factor enhancing the acidity, such as the presence of a dipole or electronegative atom (as in the nitrile functional group, CN). Alcohols,Phenols and Ethers Chemistry Practice questions, MCQs, Past Year Questions (PYQs), NCERT Questions, Question Bank, Class 11 and Class 12 Questions, NCERT Exemplar Questions and PDF Questions with answers, solutions, explanations, NCERT reference and difficulty level A proton, H+, is a strong Lewis acid; it attracts electron pairs very effectively, so much so that it is almost always attached to an electron donor. The amino proton is the most acidic. A pKa may be a small, negative number, such as -3 or -5. Some not-so-acidic compounds. The most acidic functional group usually is holding the most acidic H in the entire molecule. Looked at another way, a strong Bronsted acid gives up a proton easily, becoming a weak Bronsted base. Equation \(\ref{First}\) applies to a neutral acid such as like HCl or acetic acid, while Equation \(\ref{Second}\) applies to a cationic acid like ammonium (NH4+). By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Accessibility StatementFor more information contact us atinfo@libretexts.org. The best answers are voted up and rise to the top, Not the answer you're looking for? We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Why does Acts not mention the deaths of Peter and Paul? pKa can sometimes be so low that it is a negative number! Find a pKa table. Experimental in this sense means "based on physical evidence". Now, lets learn how to choose a suitable acid for protonating a given compound. Notice that in this case, we are extending our central statement to say that electron density in the form of a lone pair is stabilized by resonance delocalization, even though there is not a negative charge involved.
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