ACIDS AND BASES I
20 AUGUST 2013
Lesson Description
In this lesson, we:
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Discuss properties of acids and bases
List common acid and bases
Define acids and bases
Discuss conjugate acid-base pairs
Discuss ampholytes
Key Concepts
Properties of Acids and Bases
Acids
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taste sour
are electrolytes
change the colour of indicators
react with bases to form a salt and water
Bases
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taste bitter
feel soapy
are electrolytes
change the colour of indicators
react with acids to form a salt and water
Common Acids and Bases
Common Acids
Formula
Name
Use
HCl
Hydrochloric acid
Stomach acid
H2SO4
Sulphuric acid
Car batteries
HNO3
Nitric acid
Fertilizers, explosives
CH3COOH
Ethanoic acid (acetic acid)
Vinegar
H3PO4
Phosphoric acid
Fertilizers
Common Bases
Formula
Name
Use
NaOH
Sodium hydroxide
Oven and drain cleaner
NH3
Ammonia
Fertilizers
Mg(OH)2
Magnesium hydroxide
Antacids
NaHCO3
Sodium hydrogen carbonate
Baking powder
Na2CO3
Sodium carbonate
Detergents
Arrhenius’ Definitions
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An acid is any compound that dissociates when it is dissolved in water to produce hydrogen ions (H ).
For example:
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HCl(aq)  H (aq) + Cl (aq)
A base is any compound that dissociates when it is dissolved in water to produce hydroxide ions
(OH ).
For example:
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NaOH(aq)  Na (aq) + OH (aq)
Brønsted-Lowry Definitions
Acids are defined as proton donors
For example:

Bases are defined as proton acceptors
For example:
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Together these reactions show the complete reaction between sulphuric acid and ammonia:
Conjugate Acid-Base Pairs
During the reaction between an acid and base, the acid donates protons to the base. The acid has
now become a base as it is able to accept protons. During the same reaction, the base accepts
protons from the acid and thus becomes an acid.
For example:
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– conjugate base is
– conjugate acid is
Ampholytes
An ampholyte is a substance that can act as an acid or a base, depending on the nature of the other
reactant.
For example:
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-
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1. NH3 + H2O  NH4 + OH : The water acts as an acid and donates a H ion to NH3
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2. HCN + H2O  H3O + CN : The water acts as a base and accepts a H ion from HCN
Questions
Question 1
Give the conjugate base for the following:
a.) HNO3
b.) H2SO4
c.) H3PO4
Question 2
Give the conjugate acid for the following
a.) NaOH
b.) KOH
c.) Mg(OH)2
Question 3
Identify the conjugate acid-base pairs in the following reactions
a.) HCl + NaOH  NaCl + H2O
b.) H2SO4 + 2KOH  K2SO4 + H2O
c.) NaOH + HNO3  NaNO3 + H2O
Question 4
Use relevant reactions to show that the following are ampholytes
a.)
b.)