solut07 - CHAPTER SEVEN ACIDS AND BASES Nature of Acids and...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
146 CHAPTER SEVEN ACIDS AND BASES Nature of Acids and Bases 16. a. HClO 4 (aq) + H 2 O(l) H 3 O + (aq) + ClO 4 - (aq). Only the forward reaction is indicated since HClO 4 is a strong acid and is basically 100% dissociated in water. For acids, the dissociation reaction is commonly written without water as a reactant. The common abbreviation for this reaction is: HClO 4 (aq) H + (aq) + ClO 4 - (aq). This reaction is also called the K a reaction as the equilibrium constant for this reaction is designated K a . b. Propanoic acid is a weak acid, so it is only partially dissociated in water. The dissociation reaction is: CH 3 CH 2 CO 2 H(aq) + H 2 O(l) _ H 3 O + (aq) + CH 3 CH 2 CO 2 - (aq) or CH 3 CH 2 CO 2 H(aq) _ H + (aq) + CH 3 CH 2 CO 2 - (aq). c. NH 4 + is a weak acid. Similar to propanoic acid, the dissociation reaction is: NH 4 + (aq) + H 2 O(l) _ H 3 O + (aq) + NH 3 (aq) or NH 4 + (aq) _ H + (aq) + NH 3 (aq) 17. The dissociation reaction (the K a reaction) of an acid in water commonly omits water as a reactant. We will follow this practice. All dissociation reactions produce H + and the conjugate base of the acid that is dissociated. a. HC 2 H 3 O 2 (aq) _ H + (aq) + C 2 H 3 O 2 - (aq) K a = ] O H HC [ ] O H C [ ] H [ 2 3 2 - 2 3 2 + b. Co(H 2 O) 6 3+ (aq) _ H + (aq) + Co(H 2 O) 5 (OH) 2+ (aq) K a = ] ) O H [Co( ] ) (OH ) O H [Co( ] H [ + 3 6 2 + 2 5 2 + c. CH 3 NH 3 + (aq) _ H + (aq) + CH 3 NH 2 (aq) K a = ] NH CH [ ] NH CH [ ] H [ + 3 3 2 3 + 18. Strong acids have a K a >> 1 and weak acids have K a < 1. Table 7.2 in the text lists some K a values
Background image of page 1

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

View Full DocumentRight Arrow Icon
147 for weak acids. K a values for strong acids are hard to determine so they are not listed in the text. However, there are only a few common strong acids so if you memorize the common strong acids, then all other acids will be weak acids. The strong acids to memorize are HCl, HBr, HI, HNO 3 , HClO 4 and H 2 SO 4 . a. HNO 2 is a weak acid (K a = 4.0 × 10 -4 ). b. HNO 3 is a strong acid. c. HCl is a strong acid. d. HF is a weak acid (K a = 7.2 × 10 -4 ). 19. All K b reactions refer to the base reacting with water to produce the conjugate acid of the base and OH - . a. NH 3 (aq) + H 2 O(l) _ NH 4 + (aq) + OH - (aq) K b = ] NH [ ] NH [ ] OH [ 3 + 4 - b. CN - (aq) + H 2 O(l) _ HCN(aq) + OH - (aq) K b = ] CN [ [HCN] ] OH [ - - c. C 5 H 5 N(aq) + H 2 O(l) _ C 5 H 5 NH + (aq) + OH - (aq) K b = N] H C [ ] NH H C [ ] OH [ 5 5 + 5 5 - d. C 6 H 5 NH 2 (aq) + H 2 O(l) _ C 6 H 5 NH 3 + (aq) + OH - (aq) K b = ] NH H C [ ] NH H C [ ] OH [ 2 5 6 + 3 5 6 - 20. H - (aq) + H 2 O(l) H 2 (g) + OH - (aq); OCH 3 - (aq) + H 2 O(l) CH 3 OH(aq) + OH - (aq) 21. The K a value is directly related to acid strength. As K a increases, acid strength increases. For water, use K w when comparing the acid strength of water to other species. The K a values are: HNO 3 : strong acid (K a >> 1); HOCl: K a = 3.5 × 10 -8 NH 4 + : K a = 5.6 × 10 -10 ; H 2 O: K a = K w = 1.0 × 10 -14 From the K a values, the ordering is: HNO 3 > HOCl > NH 4 + > H 2 O. 22. Except for water, these are the conjugate bases of the acids in the previous exercise. In general, the weaker the acid, the stronger the conjugate base. NO 3 - is the conjugate base of a strong acid.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This homework help was uploaded on 04/06/2008 for the course CHEM 142 taught by Professor Zoller,williamh during the Fall '07 term at University of Washington.

Page1 / 59

solut07 - CHAPTER SEVEN ACIDS AND BASES Nature of Acids and...

This preview shows document pages 1 - 3. Sign up to view the full document.

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