1 / 6

Strengths of Acids & Bases

Strengths of Acids & Bases. HCN (aq) + H 2 O (l) H 3 O + (aq) + CN - (aq). Acids:. Strong acids dissociate completely in solution. eg:. HCl (aq)  H + (aq) + Cl - (aq). or. HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq).

pravat
Download Presentation

Strengths of Acids & Bases

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Strengths of Acids & Bases HCN(aq) + H2O(l) H3O+(aq)+ CN-(aq) Acids: • Strong acids dissociate completely in solution. eg: HCl(aq)  H+(aq)+ Cl-(aq) or HCl(aq) + H2O(l)  H3O+(aq)+ Cl-(aq) [HCl]=[H+]=[H3O+] • Weak acids do not dissociate completely (they reach equilibrium.) eg: [HCN] ≠[H3O+] [HCN] ≠[H3O+] eg: A 1.0M solution of HCl has a [H3O+] of 1.0M, however a 1.0M solution of HCN will have a [H3O+] < 1.0M.

  2. NH3(aq) + H2O(l) NH4+(aq)+ OH-(aq) Bases: • Strong bases dissociate or react completely. eg: NaOH(aq)  Na+(aq)+ OH-(aq) • The concentration of NaOH dissolved equals [OH-]. Note:all of the alkali metal hydroxides are strong bases. (NaOH, KOH, LiOH, etc) • Weak bases do not dissociate or react completely. eg: • Not all of the NH3 will react, therefore the amount of NH4+ produced is not the same as the amount of NH3 initially: [NH4+] <[NH3]

  3. Weak Acid Equilibrium [H+][CN-] [H3O+][CN-] [HCN] [HCN] HCN(aq) H+(aq)+ CN-(aq) HCN(aq) + H2O(l) H3O+(aq)+ CN-(aq) eg: HCN is a weak acid: KA= or: KA= • The greater the KA the stronger the acid (ie: the higher the [H3O+]) • KA values are measured at 25C (see data booklet.) • Changing temperature will change KA.

  4. HCN(aq) H+(aq)+ CN-(aq) (x)(x) [H+][CN-] x2 [HCN] 0.25 0.25 - x eg: What is the pH of 0.25 mol of hydrocyanic acid (HCN) dissolved in 1.0L of solution? KA for HCN is 6.2 x 10-10 I 0.25 M 0 0 C - x + x + x E 0.25 - x x x Assuming x is negligible compared to 0.25 KA= 6.2 x 10-10 = = x = 1.2 x 10-5 M = [H+] pH = -log (1.2x10-5) pH = 4.90 (if this had been HCl the pH would have been 0.60)

  5. H2CO3(aq) H+(aq)+ HCO3-(aq) (3.2x10-4)2 [H+][HCO3-] 0.24 [H2CO3] eg: Calculate KA for carbonic acid (H2CO3) if a 0.24M solution of the acid has a pH of 3.49. pH = 3.49 [H+]= 3.2 x 10-4 M I 0.24 M 0 0 C - 3.2x10-4 + 3.2x10-4 + 3.2x10-4 E 0.24 3.2x10-4 3.2x10-4 KA= KA= =4.3 x 10-7

  6. H3PO4(aq) H+(aq)+ H2PO4-(aq) H2PO4-(aq) H+(aq)+ HPO42-(aq) HPO42-(aq) H+(aq)+ PO43-(aq) Note:Polyprotic acids have a different KA for each H+. eg: KA1 KA2 KA3 And: KA1 >> KA2 >> KA3

More Related