TOPIC: pH
Do Now: Identify as acid, base, salt, or covalent
Electrolyte or Not
1. SALT 1. NaCl
6. CaI2 6. SALT ELECTROLYTE
ELECTROLYTE
2. C2H5OH
2. COVALENT
-NO
7. HF
3. H2SO4
3. ACIDELECTROLYTE
8. Mg(OH)2
4. NaOH
4. BASEELECTROLYTE
9. NH3
5. C12H22O11
5. COVALENT
-NO
7. ACID- WEAK
ELECTROLYTE
8. BASEELECTROLYTE
9. BASE- WEAK
ELECTROLYTE
10.CH3COOH
10. ACIDWEAK
ELECTROLYTE
Acid, Base, or Neutral
• Neutral solution: [H+1] = [OH-1]
• Acidic solution: H+1 > OH-1
• Basic solution: OH-1 > H+1
pH= LESS THEN 7
pH= GREATER THEN 7
pH scale measure how acidic/basic
a substance is.
Ranges from 0-14
0 more acidic
more basic 14
more alkaline (another word for basic)
Logarithmic scale
(based on powers of 10)
each decrease of one unit of pH represents a 10x
increase in H+ concentration
E: pH 4 is ten times more acidic then pH 5
Ex: pH 10 is ten times more basic then pH 9
Calculating pH
• pH=-log [H+]
– [H+] = concentration
– Ex. 0.01M HCl has a pH of?
• pH = -log(0.01)
• pH=2
Concentration from pH
• Which is more concentrated a HCl
solution with a pH or 2 or 3?
– pH 2 is 10 times more concentrated
(remember changes by 10)
– Try it
• Antilog (2nd log) 2 = 0.01M
• Antilog 3 = 0.001M
Try to remember: The lower the pH – the
high the concentration of H+ ions
So how do you find pH of a base?
• All you have are OH- ions
– ONLY CAN CALC pOH
• pOH=-log [OH-]
– [OH-] = concentration
– pH + pOH = 14
– So 14 – pOH = pH
– Ex. 0.01M NaOH has a pH of?
• pOH = -log(0.01)
• pOH=2
• pH = 14-2 = 12
pH range
• 0 to 14
–with 7 being neutral
• pH = 0, strongly acidic
• pH = 14, strongly basic
Because it’s based on powers of 10
there is a trick
• If molarity of acid is .001M =10-3 pH = 3
• If molarity of acid is .00001M = 10-5 pH = 5
• If molarity of base is .001M = 10-3 pOH = 3
pH 14-3 = 11
• If molarity of base is .00001M = 10-5 pOH = 5
pH 14-5 = 9
•If pH = 4
•
+1
[H ]
=?
• pOH = ?
•
-1
[OH ]
=?
Antilog(-pH) = [H+1]
Antilog(-4) = 1 x 10-4 M
pH + pOH = 14
4 + X = 14
X =10
Antilog(-10) = [OH-1]
1x10-10 M = [OH-1]
• If the
-1
[OH ]
• pOH = ?
• pH = ?
•
[H+1]
=?
=1X
-3
10 M
pOH = -log[OH-1]
= -log(10-3) = 3
pH + pOH = 14
X + 3 = 14
X = 11
Antilog(-11) = 1x10-11 M
• If the [H+1] = 1 x 10-5 M
• The pH = ?
pH=-Log (10-5)
=5
• The pOH = ? pH + pOH =14
5+x =14
X=9
• The [OH-] = ? Antilog(-9) = 1x10-9M
How to safely test pH
• Instruments – use a pH meter
• Indicators – use a series of indicators
• See if the substance reacts with a
metal other than Cu, Ag, or Au
• NEVER “taste”
Indicator
• substance that changes color over narrow pH
range
• Use several indicators to narrow down pH range
of substance
Practice using table M
1. What indicator is yellow with a pH 9.8
2. Which indictor is blue with a pH of 5.6
0-3.0Orange3.1.-4.4
Green
Pink
Purple
0-3.7
3.8-5.4
Green
Green
4.5-14
7.7-14
8.4-14
5.5-14
9.7-14