4_nano_acid_base_post

4_nano_acid_base_post - Review of acid-base reactions pH =...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
4. Acid/base 1 pH = -log[H + ] pOH = -log[OH] k w = [H + ][¯OH] = 1 x 10 -14 pH + pOH = 14 neutral solution [H + ] = [ ¯OH] = 1 x 10 -7 pH = 7 acidic solution [H + ] > 1 x 10 -7 pH range 0 to 7 basic solution [H + ] < 1 x 10 -7 pH range 7 to 14 General formula for an acid HA; for a base B HA H + + A¯ B + H 2 O B + H + ¯OH k a = [H + ][A¯] k b = [¯OH][B + H] [HA] [B] taking the log of both sides Henderson-Hasselbalch equations pH = pk a + log[A¯] pOH = pk b + log[B + H] [HA] [B] strong acid [H + ] , k a , pk a strong base [¯OH] , k b , pk b weak acid [H + ] , k a , pk a weak base [¯OH] , k b , pk b relationship between conjugate acid base pairs k a x k b = k w =1 x 10 -14 pk a + pk b = 14 Brønsted-Lowry acids and bases Review of acid-base reactions
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4. Acid/base 2 Why do acids have different acidities? What makes a strong acid a strong acid? An acid is strong if it’s conjugate base is stable. If the base is not stable it is reactive and will react with a proton and shift the equilibrium to the left in the following equilibrium. H AA ¯ + H + Hence the strength of an acid is inversely related to the strength of its conjugate base. What makes the base stable? You must look at the structure of the molecule. What is the hybridization of the atom? Is the charge on an electronegative atom? Is the electronegative atom large so that the charge is spread over a larger area ? Can the charge be delocalized throughout the molecule? All of these must be considered Acidity increases with increasing anion stability Review of acid-base reactions
Background image of page 2
4. Acid/base 3 1. What atom is the charge on? Acidity increases with increasing anion stability The more electronegative an atom, the greater its ability to carry a negative charge. Remember, electronegativity is the measure of an elements affinity for an electron or its ability to accept an electron. H AA ¯ + H + List the following compounds in order of decreasing acidity CH 4 , NH 3 , CH 3 OH, HF B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Al 1.5 Si 1.8 P 2.1 S 2.5 Cl 3.0 Ga 1.8 Ge 2.0 As 2.2 Se 2.6 Br 2.8 Te 2.1 I 2.5 ¯ CH 3 ¯ NH 2 CH 3 O ¯ F ¯ + H + + H + + H + + H + 1 2 3 4 A) 1 > 2 > 3 > 4 B) 4 > 3 > 2 > 1 C) 4 > 2 > 3 > 1 D) 1 > 4 > 3 > 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4. Acid/base 4 1. What atom is the charge on? A larger anion can disperse the negative charge over a larger volume and thus increases the stability of the conjugate base which is more important than electronegativity when comparing elements down a column in the periodic table. Thus use electronegativity when comparing atoms in the same row and size when comparing atoms in the same column H AA ¯ + H + List the following compounds in order of decreasing acidity 1) HCl 2) HBr 3) HF 4) HI B 2.0 C 2.5 N 3.0 O 3.5 F 4.0 Al 1.5 Si 1.8 P 2.1 S 2.5 Cl 3.0 Ga 1.8 Ge 2.0 As 2.2 Se 2.6 Br 2.8 Te 2.1 I 2.5 A) 1 > 2 > 3 > 4 B) 4 > 2 > 1 > 3 C) 4 > 2 > 3 > 1 D) 1 > 4 > 3 > 2
Background image of page 4
4. Acid/base
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 07/18/2011 for the course NE 122 taught by Professor Nano during the Winter '09 term at Waterloo.

Page1 / 33

4_nano_acid_base_post - Review of acid-base reactions pH =...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online