Download presentation
Presentation is loading. Please wait.
Published byDakota Riggins Modified over 10 years ago
1
Chapter 16: Equilibrium in Acid-Base Systems 16.1a: Self-ionization of Water K w pH and pOH
2
Self-ionization of water If water is a weak electrolyte, what does it ionize in to? H 2 O (l) ⇄ OH - (aq) + H + (aq) OR 2H 2 O (l) ⇄ OH - (aq) + H 3 O + (aq) the concentrations of the ions are only 1.0 x 10 -7 M at 25°C the product of these concentrations will remain constant for any solution at the same temperature
3
Self-ionization of Water concentrations or molarities can be written with brackets For example: concentration of A = [A] = 2.0 M Kw:Kw:Kw:Kw: the ionization constant of water the ionization constant of water the product of [OH - ] and [H + ] the product of [OH - ] and [H + ] at 25 o C
4
KwKwKwKw subject to the same restricition as any other equilibrium constant (T, P) Will acidic solutions have more H + or OH - ? [H + ]>[OH - ]: acidic [H + ]>[OH - ]: acidic [OH - ]>[H + ]: basic [OH - ]>[H + ]: basic [OH - ]=[H + ]: neutral [OH - ]=[H + ]: neutral can find the [OH - ] or [H + ] from a mole ratio of the dissociation or reaction in the water of the acid or base
5
Example 1 Calculate the H + concentration in a 1.5 M Ca(OH) 2 solution What does the Ca(OH) 2 create in solution? What does the Ca(OH) 2 create in solution? Ca(OH) 2 Ca 2+ + 2OH - Ca(OH) 2 Ca 2+ + 2OH - can calculate the OH - concentration can calculate the OH - concentration use K w to calculate the H + concentration use K w to calculate the H + concentration
6
Example 2 Calculate the H + and OH - concentration of a 1.0x10 -4 M solution of HNO 3 Find the [H + ] from mole ratio Find the [H + ] from mole ratio Find [OH - ] from K w and [H + ] Find [OH - ] from K w and [H + ] HNO 3 H + + NO 3 -
7
pH scale more convenient than using concentrations pH=-log [H + ] pOH=-log [OH - ] pH increases as [H + ] decreases pH < 7: acid pH > 7: base pH = 7: neutral
8
pH for any solution at 25 o C: -log[H + ] + -log[OH - ] = -log([H + ][OH - ] -log[H + ] + -log[OH - ] = -log([H + ][OH - ] = -log(1.0x10 -14 ) =14 = -log(1.0x10 -14 ) =14 14.00 = pH + pOH
9
Example 3 Find the pH of a 1.0x10 -3 M NaOH solution find [OH - ] using mole ratio find [OH - ] using mole ratio find [H + ] from K w find [H + ] from K w find pH from [H + ] find pH from [H + ]OR find pOH from [OH - ] find pOH from [OH - ] find pH from pOH find pH from pOH
10
Example 3 sol’n OR
11
Calculating [H + ] and [OH - ] reverse the pH equation The pH of a solution is 7.52. Find the [H+] and [OH-] and determine whether it is acidic, basic, or neutral. [OH - ] > [H + ] so solution is basic
12
Example A shampoo has a pH of 2.53. Calculate the pOH, [H + ] and [OH - ]. Is it acidic, basic, or neutral? pH < 7 so acidic
13
Homework Textbook p716 #1-6 p718 #7 LSM 16.1B
Similar presentations
© 2024 SlidePlayer.com Inc.
All rights reserved.