Predicting the Products of Acid-Base Reactions
An Example
Using Bronsted Lowry Theory and Solution Chemistry
Chemistry 3202
Acid-Base Reactions Example 1
Determine the acid-base neutralization reaction that occurs between
aqueous solutions of sodium hydrogen sulfite and ammonium bicarbonate.
(Use the Lowry Bronsted Theory in The Five Step Method)
- List the species actually in solution.
- Identify Bronsted-Lowry Acids (A) and Bases (B)
- Identify the Strongest Acid (SA) and Strongest Base (SB)
- Write the Reaction between the Strongest Acid and Strongest Base
- Determine the Extent of the Reaction
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Step 1 - List the species.
Determine the acid-base neutralization reaction that occurs between
aqueous solutions of sodium hydrogen sulfite and ammonium bicarbonate.
- Think!
- What species will be present upon initially mixing the solution?
- Construct a list of all species.
- Include the solvent!
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Step 1 - List the species.(Completed)
|
|
|
|
|
| Na1+(aq), |
HSO31-(aq), |
NH41+(aq), |
HCO31-(aq), |
H2O(l), |
|
|
|
|
|
Next is Step 2 - Identify Acids (A) and Bases (B).
Hints:
- Acids must have a proton (H1+) to give away!
- Bases can only accept protons to make known species?
- Check ion tables for status of possible ions that would form.
- Neutral species - check acid tables (but other possibilities!).
- Unusual for a positive ion to accept a proton! (charges repel)
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Step 2 - Identify Acids & Bases (Done!)
|
A |
A |
A
|
A |
| Na1+(aq), |
HSO31-(aq), |
NH41+(aq), |
HCO31-(aq), |
H2O(l), |
|
B |
|
B |
B |
Next - Identify the Strongest Acid (SA) and Strongest Base (SB)
Hint: Use the table of Acid-Base Strengths.
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The Strongest Acid & Base (Done)
|
SA |
A |
A
|
A |
| Na1+(aq), |
HSO31-(aq), |
NH41+(aq), |
HCO31-(aq), |
H2O(l), |
|
B |
|
SB |
B |
Next is Step 4 - Write the Reaction between the Strongest Acid and Strongest Base.
Use the Bronsted Lowry ideas to transfer a proton from the strongest acid to the strongest base to determine what the products will be.
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React the Strongest Acid & Base
|
SA |
A |
|
A |
| Na1+(aq), |
HSO31-(aq), |
NH41+(aq), |
HCO31-(aq), |
H2O(l), |
|
B |
|
SB |
B |
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
-???-
|
____?____
|
+
|
____?____
|
Next - Transfer the proton from the acid to the base to get the products.
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React the Strongest Acid & Base (Done)
|
SA |
A |
|
A |
| Na1+(aq), |
HSO31-(aq), |
NH41+(aq), |
HCO31-(aq), |
H2O(l), |
|
B |
|
SB |
B |
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
-???-
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
Next is Step 5 - Determine the Extent of the Reaction.
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Step 5 - Determining The Extent Rxn 1
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
-???-
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
Determine if the reaction is quantitative (stoichiometric) or equilibrium.
- If strong acid or strong base is involved, reaction is quantitative.
- This means hydronium (H3O1+) or hydroxide (OH1-).
- Use a single reaction arrow.
- ie ---->
- NOT the case here! So...
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Step 5 - Determining The Extent Rxn 2
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
-???-
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
Determine if the reaction is quantitative (stoichiometric) or equilibrium.
Step 5 - Determining The Extent Rxn 2
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
-???-
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
A
(Acid) |
|
|
|
|
|
CA
(Conjugate Acid)
|
- In the table the conjugate acid is stronger (listed higher).
- Stronger acid 'drives' the equilibrium (wins out?) to 'opposite side'.
- In this case equilibrium favours reactants.
- Third equilibrium arrow points to products.
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Step 5 - Determining The Extent Rxn 3
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
WA
(weaker) |
|
|
|
|
|
SCA
(stronger)
|
Finished acid-base reaction complete with arrows.
We would come to the same conclusion using the "finger method"...
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Step 5 - Determining The Extent Rxn 4
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
|
A |
|
B |
|
|
|
|
With the finger method:
- Use reactant acid & base (Identified previously as SA & SB).
- Place left hand finger on acid in acid column.
- Place right hand finger on base in base column.
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Step 5 - Determining The Extent Rxn 5
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
|
A |
|
B |
|
|
|
|
- If left finger is above right finger...
- Acid-base relationship is relatively strong (higher in acid - lower in base).
- Reaction tendancy is to shift to products.
- Equilibrium will favour products.
- If left finger is below right finger...
- Acid-base relationship is relatively weak (lower in acid - higher in base).
- Reaction tendancy is to stay as reactants.
- Equilibrium will favour reactants.
Get the same result as before, with equilibrium favouring reactants.
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Summary
Determine the acid-base neutralization reaction that occurs between
aqueous solutions of sodium hydrogen sulfite and ammonium bicarbonate.
|
SA |
A |
|
A |
| Na1+(aq), |
HSO31-(aq), |
NH41+(aq), |
HCO31-(aq), |
H2O(l), |
|
B |
|
SB |
B |
|
HSO31-(aq)
|
+
|
HCO31-(aq)
|
|
SO32-(aq)
|
+
|
H2CO3(aq)
|
|
|
|
|
|
|
|
|
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