Strong and Weak Acids and Bases
Strength of Acids H2SO4 HSO4 - + H + HNO3 NO3 - + H + Strong Acids HCl Cl - + H + H3PO4 H2PO4 - + H + Phosphoric acid Moderate Acid CH3COOH CH3COO - + H + Acetic acid HF F - + H + Weak Acids H2CO3 HCO 3 - + H + HCN CN - + H +
HCl is a Strong Acid HF is a Weak Acid
Strong Bases NaOH Na + + OH - KOH K + + OH - LiOH Li + + OH - Ba(OH)2 Ba 2+ + 2 OH - sparingly soluble in water
Weak Bases: ammonia NH3 + H2O NH4 + + OH - acetate CH3COO - + H2O CH3COOH + OH - carbonate CO3 2- + H2O HCO3 - + OH -
Acidity and Basicity of Aqueous Solutions
Water is Amphoteric HCl + H2O ----------> Cl - + [H3O] + - + NH3 + H2O ----------> NH4 + + [HO] - + -
Water can act as an acid or base. (It s amphoteric ) H2O (l) + H2O (l) [H3O]+ (aq) + [HO]- (aq) proton acceptor proton donor + [ ] + + [ ] - In pure water this reaction takes place to a very small extent. Concentration of hydronium ions = Concentration of hydroxide ions [ H3O + ] = 1 x 10-7 = [ OH - ] = 1 x 10-7 M
A neutral solution is defined as a solution in which [ H3O + ] = 1 x 10-7 M & [ OH - ] = 1 x 10-7 M
1. What is the hydrogen ion concentration in a 1.0 M hydrochloric acid solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M HCl H + (aq) + Cl - (aq) 2. What is the hydronium ion concentration in a 1.0 M sulfuric acid solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M H2SO4 2 H + (aq) + SO4 - (aq)
3. What is the hydroxide ion concentration in a 1.0 M potassium hydroxide solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M KOH K + (aq) + OH - (aq) 4. What is the hydroxide ion concentration in a 1.0 M calcium hydroxide solution? A) 0.5 M B) 1.0 M C) 1.5 M D) 2.0 M E) 4.0 M Ca(OH)2 Ca 2+ (aq) + 2 OH - (aq)
Acidic Solution Basic Solution [H+] 10 0 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 H+ H+ H+ H+ H+ [] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 10 0 [H+] vs []
Ion Product of Water = Kw =[H3O+][]=1.0 x 10-14 [H+] 10 0 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 H+ H+ H+ H+ H+ [] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 10 0 [H+] vs []
5. If the [H3O+] of a solution is 3.6 x10-8, what is the []? Kw =[H3O+][]=1.0 x 10-14 (3.6 x10-8 )[]=1.0 x 10-14 []=(1.0 x 10-14 )/(3.6 x10-8 ) []=2.8 x10-7
6. If the [] of a solution is 4.6 x10-4, what is the [H3O+]? Kw =[H3O+][]=1.0 x 10-14 [H3O+](4.6 x10-4 )=1.0 x 10-14 [H3O+]=(1.0 x 10-14 )/(4.6 x10-4 ) [H3O+] =2.2 x10-11
A neutral solution is defined as a solution in which [ H3O + ] = 1 x 10-7 M & [ OH - ] = 1 x 10-7 M An acidic solution is defined as a solution in which [ H3O + ] > 1 x 10-7 M & [ OH - ] < 1 x 10-7 M A basic solution is defined as a solution in which [ H3O + ] < 1 x 10-7 M & [ OH - ] > 1 x 10-7 M
[H+] vs [] [H+] 10 0 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 H+ H+ H+ H+ H+ [] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 10 0 ACIDIC BASIC
7. A solution with H3O + concentration of 2 x 10 4 M can be described as A) basic. B) acidic. C) neutral. 8. A solution with H3O + concentration of 2.8 x 10 7 M can be described as A) basic. B) acidic. C) neutral. 9. A solution with H3O + concentration of 2.2 x 10 11 M can be described as A) basic. B) acidic. C) neutral.
Because of the wide range of values for hydronium ion concentrations (from 0.00000000000001 M to 100 M) a logarithmic scale (the ph scale) is usually used. The Log Function
ph vs poh ph 0 1 3 5 7 9 11 13 14 [H+] 10 0 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 H+ H+ H+ H+ H+ [] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 10 0 poh 14 13 11 9 7 5 3 1 0 ph + poh =14
1 10-1
10. How many times more acidic is a solution with a ph of 1 (stomach acid) than a solution with a ph of 7 (blood)? A) 6 B) 7 C) 7000 D) 1,000,000 11. How many times more basic is a solution with a ph of 12 (household ammonia) than a solution with a ph of 5 (coffee)? A) 2.4 B) 7 C) 700 D) 10,000,000
12. What is the ph of 1.0 x 10-3 M HCl? ph = -log [H3O + ] ph = -log (1.0 x 10-3 ) ph = -(-3.00) = 3.00 13. What is the ph of a solution if [H3O + ] =2.6 x 10-10? ph = -log [H3O + ] ph = -log (2.6 x 10-10 ) ph = -(-9.58) = 9.58
14. What is [H3O + ] of a solution with a ph of 8.00? [H3O + ] = 10 -ph [H3O + ] = 10 -(8.00) [H3O + ] = 1.0 x 10-8 M 15. What is [H3O + ] of a solution with a ph of 6.22? [H3O + ] = 10 -ph [H3O + ] = 10 -(6.22) [H3O + ] = 6.0 x 10-7 M
16. What is [OH ] in an aqueous solution with a ph of 10.34? A) 4.6 x 10 11 M B) 2.2 x 10 4 M C) 4.6 x 10 3 M D) 2.2 x 10 10 M E) 1.0 x 10 14 M [H3O + ] = 10 -ph [H3O + ] = 10 -( 10.34) [H3O + ] = 4.6 x 10-11 M Kw =[H3O+][]=1.0 x 10-14 (4.6 x10-11 )[]=1.0 x 10-14 []=(1.0 x 10-14 )/(4.6 x10-11 ) []=2.2 x10-4
ACIDIC BASIC ph 0 1 3 5 7 9 11 13 14 [H+] 10 0 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14 H+ H+ H+ H+ H+ [] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 10 0 poh 14 13 11 9 7 5 3 1 0 Ion Product of Water = Kw =[H3O+][]=1.0 x 10-14 ph + poh =14
Buffers Buffer System - A solution which resists a change in ph when small amounts of acid or base are added Components of a Buffer System A weak acid, and A salt of that weak acid or A weak base, and A salt of that weak base
17. Which of the following pairs of components would create a buffer solution? HCl and NaOH NaOH and NaCl KCl and NaCl H2CO3 and NaHCO3 HF and KF CH3COOH and CH3COO - Na +
How Does the Acetate Buffer System Work? 1) An acetate buffer system contains CH3COOH and CH3COO - (acetic acid) (acetate anion) 2) The acetate anion reacts with excess acid (H + ) CH3COO - + H + CH3COOH 3) The acetic acid component reacts with excess base (OH - ) CH3COOH + OH - CH3COO -
Buffer systems A buffer contains significant amounts of a weak acid and its conjugate base. The acid consumes any added base, and the base consumes any added acid. In this way, a buffer resists ph change. How Does the Acetate Buffer System Work?
ph changes in pure water and a buffer solution A comparison of the change in ph when 0.010 mol of acid and 0.010 mol of base are added to 1.0 L of pure water and to 1.0 L of 0.10 M acetic acid-0.10 M acetate ion buffer.
Two Important Physiological Buffer Systems H2CO3(aq) H + (aq) + HCO3 - (aq) The bicarbonate buffer system operates in the bloodstream. H2PO4 - (aq) H + (aq) + HPO4 2- (aq) The dihydrogen phosphate buffer system operates within cells.