lecture 19.2- ph
DESCRIPTION
Section 19.2 Lecture for Honors and Prep ChemistryTRANSCRIPT
BELLWORK- Label pairs
Identify the conjugate acid-base pairs
a. H2S + H2O HS- + H3O+
b. HClO4 + H2O ClO4- + H3O+
c. NH3 + H2O NH4+ + OH-
d. H2O + HNO3 NO3- + H3O+
The pH scale measures the hydrogen ion concentration[H+]
of a solution.
A pH of 7 is neutral
A pH less than 7 is acidic (litmus is red)
A pH greater than 7 is basic (litmus is blue)
The pH scale ranges from below zero (very acidic) to above14 (very basic)
The pH scale is not linear.The pH scale is logarithmic.
pH = -log[H+] [H+] = 1.0 x 10-2 pH = 2 very acidic[H+] = 1.0 x 10-3 pH = 3 acidic
A solution with pH of 2 contains 10 times as much H+ as a solution with pH of 3.
Calculate pHpH = -log [H+]
[H+] = 1.0 x 10-7M
[H+] = 5.0 x 10-5M
Calculate pHpH = -log [H+]
[H+] = 1.0 x 10-7M pH= -(exponent) =7
[H+] = 5.0 x 10-5M
Calculate pHpH = -log [H+]
[H+] = 1.0 x 10-7M pH= -(exponent) =7
[H+] = 5.0 x 10-5M pH is between 4&5
Calculate pHpH = -log [H+]
[H+] = 1.0 x 10-7M pH= -(exponent) =7
[H+] = 5.0 x 10-5M pH is between 4&5
to CHECK with calculator1.Enter concentration in calculator
2.Press log key
3.Change sign to positive
OR in the reverse order depending on your calculator!
Calculate [H+] given pH
pH = 7.0
pH= 8.5
Calculate [H+] given pH
pH = 7.0 [H+]= 1x10-7
pH= 8.5
Calculate [H+] given pH
pH = 7.0 [H+]= 1x10-7
pH= 8.5 [H+]= 3.2x10-9
Calculate [H+] given pH
pH = 7.0 [H+]= 1x10-7
pH= 8.5 [H+]= 3.2x10-9
1. Enter pH value in calculator
2. Press the +/- key
3. Press the 10x key
OR in the reverse order depending on your calculator!
From pH0 to pH14 the H+ concentration decreases 100,000,000,000,000 times!!
Relationship between [H+] and [OH-]
[H3O+][OH-] = 1.0 x 10-14
ALWAYS!!
Relationship between [H+] and [OH-]
[H3O+][OH-] = 1.0 x 10-14
ALWAYS!!
If [H+] = 1.0 x 10-5 then,
[OH-] = 1.0x10-14/ 1.0x10-5 = 1 x 10-9
SUBTRACT THE EXPONENTS!
Relationship between [H+] and [OH-]
[H3O+][OH-] = 1.0 x 10-14
If [H+] = 5.0 x 10-4 then,
[OH-] = 1.0x10-14/ 5.0x10-4 = 2 x 10-11
Acidic = more H+ Basic = more OH-
pOH = -log[OH-]
pH + pOH = 14
Always!!
Relationship between pH and pOH
pH pOH
[H+] [OH-]
pH + pOH = 14
[H+][OH-]=1x10-14
pH = -log[H+]
pOH = -log[OH-]
pH pOH
[H+] [OH-]
pH + pOH = 14
[H+][OH-]=1x10-14
[H+] =10-pH
[OH-]=10-pOH
Calculate pH pOH
What is the pH of a solution with pOH = 13?
Is the solution acidic or basic?
What is the pOH of a solution with pH = 8?
Is the solution acidic or basic?
What are the concentrations of H+ and OH-?