11-18-08[lecture19]ec

11-18-08[lecture19]ec - Chem 116 Student Notes November 18,...

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Unformatted text preview: Chem 116 Student Notes November 18, 2008 (EC) Lecture 19: Acid‐Base Equilibrium Clicker Question: HPO42‐ (aq) + HCO3‐ (l) CO32‐ (aq) + H2PO4‐ (aq) (a) (b) (c) (d) base2 acid 1 base1 acid 2 Question 1: ID the acid/base on the left and their conjugate base/acid on the right Answer: D (b) is an acid (gives up H+) (c) is its conjugate base (a) is a base (receives an H+) (d) is its conjugate acid Question 2: Does the equilibrium lie primarily to the left or to the right? Answer: B Ka values given are the acid ionization constants they measure the strength of the acids (so the Ka value for HPO42‐ doesn’t need to be considered) the larger the Ka value the stronger the acid the stronger the acid, the more the equilibrium will go to the other side H2PO4‐ is the stronger of the 2 acids and is on the right so the equilibrium lies to the left pH and pOH 1. “p” just stands for “the negative log base‐10 of” a. so pH = ‐log10[H+] 2. pH measures the concentration of [H+] ions 3. pOH measures the concentration of [OH‐] ions a. pH scale of 0 (acidic) to 14 (basic) i. pH of 7 (neutral) means [H+] = [OH‐] b. there are pH values lower than 0 and higher than 14 but they are so corrosive or caustic they often eat through normal containers, so they’re not commonly measured 4. pH + pOH = 14 a. so once you find either pH or pOH you can find the other by subtracting it from 14 3 types of acid­base problems 1. Predict the pH a. Strong acid/base i. Completely dissociates so the concentration of [H+] or [OH‐] will just be the amount of the acid/base you started with ii. Strong acids include: 1. HCl, HBr, HI (but not HF which is weak) 2. H2SO4 3. HNO3 4. HClO4 iii. Strong bases include: 1. Most metal cations with OH‐ ions iv. Kw (1.0x10‐14) = [H+] × [OH‐] is the water autoionization equilibrium taking the negative log of both sides gives 14 = pH + pOH b. Weak acid/base i. Solve as you would with I C E charts ii. Ka is usually given 2. Equilibrium a. Given pH of a solution b. Figure out how much acid/base or salt must have been added to water to make the that given pH 3. Titration a. Given a solution of unknown acid/base concentration b. Neutralize with known amount of base/acid to figure out unknown concentration ...
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