Acid Base Reactions and Titration Curves

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Acid Base Reactions and Titration Curves
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Vocab

• Titrant
• Analyte
• Endpoint/Equivalence point
• Indicators

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Common Indicators
Name Acid color pH range Base color
Methyl violet Yellow 0 1.6 Blue-violet
Methyl orange Red 3.2-4.4 Yellow
Litmus Red 5-8 Blue
Phenolphthalein Colorless 8.2 - 10.0 Pink
Thymolphthalein Colorless 9.4-10.6 Blue
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Phenolphthalein Formal name 3,3-bis(4-hydroxyphe
nyl)-1(3H)-isobenzofuranone, 3,3-bis(4-hydroxyphen
yl)phthalide)

• Bronsted Acid Conj. Base
• (colorless, in acid) (pink, in base)

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Types of Reactions

• Strong Acid - Strong Base
• Weak Acid - Strong Base
• Strong Acid - Weak Base

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1. Strong Acid - Strong Base

• Example HCl NaOH --gt
• Titration Equation Ma Va Mb Vb

Equivalence Pt
pH ____
If 50. mL of HCl was titrated with 0.050 M NaOH,
what is the HCl
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A 25. mL sample of HCl titrated using 50 mL of
0.050 M NaOH. Sketch this curve.
pH
Volume of Base Added
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2. Weak Acid - Strong Base

• Example CH3COOH NaOH --gt
• MVMV

pH
9
2. Weak Acid - Strong Base

• Important Points
• pH pKa when halfway to equivalence point
• The formation of a conjugate base A- will make
  the solution BASIC at equivalence, so pH gt 7

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3. Weak Base - Strong Acid

• Example NH3 HCl --gt
• MVMV

pH pKb
pH
12.5
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3. Weak Base - Strong Acid

• Important Points
• pH pKb at halfway to equivalence point
• The formation of a conjugate acid BH will make
  the solution ACIDIC at equivalence, so pH lt 7

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Titration of Diprotic Acids

• 2 equivalence pts