Acid Reactions, Acid-Base Titration - General Chemistry - Lecture Slides, Slides for Chemistry. B R Ambedkar National Institute of Technology
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Acid Reactions, Acid-Base Titration - General Chemistry - Lecture Slides, Slides for Chemistry. B R Ambedkar National Institute of Technology

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General Chemistry course covers the fundamentals of chemistry which includes: structure of atom/molecules, thermodynamics, stoichiometry, equilibrium and acid base chemistry. Keywords from these slides are: Acid Reaction...
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Microsoft PowerPoint - Acid Reactions, Acid-Base Titration [Compatibility Mode]

Acid Reactions I

Acids & Active Metals: • Single replacement reactions • Active metals (K, Na, Ca, Mg, Al, Zn, Fe, Sn) • Produce H2 • Oxidation-reduction reactions

1

Example: calcium solid + HCl

Ca (s) + HCl (aq)  CaCl2 (aq) + H2 (g) 2

Zn and HCl

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Acid Reactions II Acids, Carbonates and Bicarbonates

• H+ from acid transferred to carbonate • Carbonate breaks down rapidly • Products:

• CO2

• H2O

• salt (ionic compound)

2

Example:

NaHCO3 (aq) + HCl (aq)  H2CO3 (aq) + NaCl (aq)

CO2 (g) + H2O (l)

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Acid Reactions III

Neutralization • Reactants: acid + base • Products: water + salt

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Example:

HCl (aq) + NaOH (aq)  HOH (l) + NaCl (aq)

H2O (l) H+ (aq) + OH- (aq) 

Molecular equation:

Net ionic equation:

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Acid-Base Titration • Titration: Neutralize an unknown acid sample with a

known amount of base

• Indicator: changes color when pH changes Example: phenolphthalein

4

Colorless (acidic)

Pink (basic)

Add base

Add base

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Acid-Base Properties of Salt Solutions • Salts dissolve in water • Which salts form…

• Neutral Solutions?

• Basic Solutions? • Acidic Solutions?

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cation from strong base and anion from strong acid

NaNO3

NaNO3 (s) Na+ (aq) + NO3 - (aq) 

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Basic and Acidic Salt Solutions • Basic solutions form from salts that contain:

• Acidic solutions form from salts that contain:

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cation from strong base and anion from weak acid

NaF NaF (s) Na+ (aq) + F - (aq)

cation from weak base and anion from strong acid

NH4Cl NH4Cl (s) NH4+ (aq) + Cl - (aq)

 OH2

 OH2

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Buffers • Buffer solutions resist a change in pH

– Ex. Blood (pH ~ 7.4)

• Acid must neutralize small amounts of base • Base must neutralize small amounts of acid • Acid and base must not neutralize each other

7

Use conjugate acid-base pairs!

CH3COOH (aq) + H2O (l) CH3COO - (aq) + H3O+ (aq)

Added in as salt (NaCH3COO)

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Buffers

• weak acid + its salt (containing conjugate base)

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CH3COOH (aq) + H2O (l) CH3COO - (aq) + H3O+ (aq)

You have prepared a buffer with 0.90 M CH3COOH and 1.2 M CH3COO-. (Ka for acetic acid = 1.8 x 10-5).

What is the equilibrium expression for this buffer?

What is the [H3O+] in this solution?

What is the pH of this solution?

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Making a buffer

We want to make 100. mL of a pH 4 citric acid/sodium citrate buffer with an acid concentration of 0.5 M.

We are given solid sodium citrate (294 g/mol) and

5.0 M citric acid. The pKa of citric acid is 3.15. 9

 

  

 

[acid] [base]logpKpH a

Henderson-Hasselbalch equation

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