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-log Ka = -log [H3O+] pKa = pH Ka = 10-pKa. The pKa value is used to choose a buffer when needed. … HCO 2 H. HCO 2-Methanoate ion. As I mentioned I THINK NH4CL will come apart...leave NH4 and Cl-. NH4 on the other hand is a strong acid (c.a of a weak base). 1.8 * 10-4. The value of Ka is used to calculate the pH of weak acids. Finding the Ksp of PbCl2 when Pb(NO3)2 and NaCl are mixed. Ka is the equilibrium constant for the dissociation reaction of a weak acid. [NH4+]  =  .50 M, Ka = [NH3][H+]/[NH4+]  =  x^2/.5 = 10^-9.20, Since x was set equal to [H+], pH will equal - log x, The NH4+ then acts as a weak acid according to the reaction: NH4 will donate it's H+ to water forming H3O+  (my bad OH- won't be a product as I mentioned!). Hydrofluoric acid, HF, is a weak acid that does not ionize completely in aqueous solution to form hydronium cations, H3O+, and fluoride anions, F−. This is in part a result of the strength of the hydrogen–fluorine bond, but also of other factors such as the tendency of HF, H 2O, and F anions to form clusters. The pKa values for organic acids can be found in However, if this is true you will be left with H2O and NH4 to react...just set up your ice table like you did before, except this time you'll be working with OH-...so be sure to change it to pH! General Understanding of Ka's, pKa's, Keqs, and more. Hydrofluoric HF F-7.2 x 10-4 3.14 Nitrous HNO2 NO2-4.0 x 10-4 3.39 Formic HCOOH HCOO-1.77 x 10-4 3.75 Lactic HCH3H5O3 CH3H5O3-1.38 x 10-4 3.86 ... Table of Acids with Ka and pKa Values* CLAS * Compiled from Appendix 5 Chem 1A, B, C Lab Manual and Zumdahl 6th Ed. Calculate the acid ionization constant, Ka, of HF, In a 0.100M solution of HF, the pH is determined to be 2.12. I guess because of the hydrogen-fluorine bond?). Calculate the pH of a 0.50M NH4Cl solution. Would Ka still be Ka = [H3O+][F-] / [HF]? Choosing an acid or base where pK a is close to the pH needed gives the best results. HF is a weak acid, but [HF] is not equal to [F-] HF H+ + F-[H+] = 10-2.12 = .00760 from the pH [H+] = [F-] since for every H+ ion produced a F- ion will be produced [HF] = .100 M - [H+] = .0924. I'm not really sure what to do with this one, exactly.                NH4+     NH3    +   H+. But, to create NH4Cl wouldn't I have to have this reaction: If so, I'm confused about how the pKa of NH4 is relevant.. You are starting with a NH4Cl solution. HF is not a strong acid (because it doesn't ionize in aqueous solution.. K a is the equilibrium constant for the dissociation reaction of a weak acid.A weak acid is one that only partially dissociates in water or an aqueous solution. Acid Dissociation Constant Definition: Ka, pH and pKa Relationship: The Henderson-Hasselbalch Equation, Definition and Examples of Acid-Base Indicator, Henderson-Hasselbalch Equation and Example, Buffer Definition in Chemistry and Biology, Henderson Hasselbalch Equation Definition, Polyprotic Acid Example Chemistry Problem. He holds bachelor's degrees in both physics and mathematics. I just finished working this one, and that's exactly what I did. -log Ka = -log [H3O+] I doubt the Cl would react here, because it's the conjugate base of a strong acid...meaning it's a weak base. Is this the correct pKa value for pyridine? Thanks! F - Fluoride ion. Ka = 10-pKa, HF is a weak acid, but [HF] is not equal to [F-], [H+] = [F-]  since for every H+ ion produced a F- ion will be produced, Ka = [H+][A-]/[HA] so plug in the values above and you can calculate the value of Ka, NH4Cl completely dissociates into NH4+  and Cl- ions, The NH4+ then acts as a weak acid according to the reaction: