Examples of acid BASE

7/30/2019 Examples of acid BASE

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Examples of Acid-Base Titrations

I. Molecular Weight of a Weak Acid

A. Weak acid whose pKa is known

B. Weak acid whose pKa is not known

C. Procedure

1. Weigh a known amount of weak acid

2. Dissolve in water

3. Titrate to Endpoint with known

concentration of strong base (NaOH)

Nb

4. Determine # ml of NaOH used, Vb


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#equiv of = NbVb (in l)

base consumed= # equiv of acid present

So

NbV

b' Number Equv. of acid'

Number g of acid weighed out

Eq. Weight of acid

Solve for Equiv. Wt.

Eq. Wt. 'Molecular Weight

Number H%

ionized

Solve for MW


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pH

11

10

9

8

7

6

5

4

3

2

10 30ml of 0.1 M HCl

II. Titration of Na2CO3 and mixtures containing

Na2CO3

A. For Na2CO3 only or Na2CO3 - Na2O

(Soda Ash)

Na2CO3 + HCl > NaCl + NaHCO3Phenolphthalein EP

NaHCO3 + HCl > NaCl + H2CO3Methyl Red EP ^

H2O + CO28


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Note: Species present at phenolphthalein &

methyl red endpoints

Effect of boiling

Volume to first & second equivalence point


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B. Mixture of Na2CO3 and NaHCO3

1. Titrate of phenolphthalein EP -

Determine Va

Na2CO3 + HCl > NaHCO3 + H2O

NaVa = # equiv HCl = # equiv of

Na2CO3 = # moles Na2CO3 = MaVa

# equiv Na2CO3 = # moles Na2CO3 at

this EP

Determine the amount Na2CO3

present in mixture

Number g Na2CO

3' Number moles x GFW

Na2CO

3


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Va

Va

10 20 30 40

ml 0.1 M HCl

pH

2. Titrate To Methyl Red EP -

Determine Va

Na2CO3 + 2 HCl -----> 2 NaCl + H2CO3NaHCO3 + HCl -----> NaCl + H2CO3


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Va

Va

10 20 30 40 50ml 0.1 N HClml 0.1 M HCl

pH

C. Mix of NaOH and Na2CO3

1. Titrate to phenolphthalein EP-Determine Va

NaOH + HCl ----> NaCl + H2O

Na2CO3 + HCl ----> NaCl + NaHCO3

2. Titrate To Methyl Red EP -Determine Va

NaOH + HCl ----> NaCl + H2O

Na2CO3 + 2HCl -----> 2NaCl + H2CO3


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D. Mixture of Na2CO3 - Na2O

1. Weigh Sample

2. Titrate to methyl red end point3. Here NaVa = # equiv HCl =

# equiv Na2CO3Based upon

2 HCl + Na2CO3 ----> 2 NaCl + H2CO3

number / Na2CO

3' number g Na2CO3

GEW

where

GEW'GFW

Na2CO

3

2

Solve for #g of Na2CO3

% Na2CO

3'

number g Na2CO

3

number g Samplex 100

% Na2O = 100 - % Na2CO3


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III. Kjeldahl Nitrogen Determination-

A. Prereduction

1. -NO2 nitro reduction

----------->

-N=N- azo reduction

----------->

2. -NH2 Amines

H O

| 2

-N- C- Amides


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B. Digestion

1. Decomposed with hot, concentratedH2SO4

[O]

Organic ----------->

C, H, N H2SO48

Use Hg+2, Cu+2, or Se


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C. Distillation

1. Neutralize with NaOH carefully

2 OH- + NH4HSO4 ----->

2. Heat to distill the NH3

3. Collect NH3 in a receiver containing

an accurately known amount of acid

A. Na & Va of HCl

NH3 + HCl ------> NH4Cl


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B. Saturated (Na), Va of H3BO3(will not need Na of Va with this

method)

NH3 + H3BO3 ------>

4. If HCl- Use known volume of HCl of

known normality

A. let NH3 react

B. Titrate excess HCl with

standardized NaOH

NaVa = Total Equiv of HCl

NbVb = # equiv of HCl Excess

NaVa-NbVb = # equiv of HCl

consumed by NH3


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5. If saturated H3BO3NH3 + H3BO3 NH4

+ + H2BO3-

satd

Titrate the H2BO3- with standardized HCl

H2BO3- + H+ -------> H3BO3 9

NaVa = equiv Acid HCl

# equiv of = # equiv = # equiv NH3HCl H2BO3

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Examples of acid BASE