Acid-Base Reactions

Learning Objective

In this lesson we will learn about the different types of acid-base reactions and the products they form.

Learning Outcomes

By the end of this lesson you will be able to:

  • Identify acid-base reactions.

  • Write the generalised chemical equations for different types of acid-base reactions.

  • Determine the products of acid-base reactions.

 

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Introduction

  • There are four main types of acid-base reactions, depending on the type of base and the products formed:
    1. Reactions between acids and metal hydroxides.
    2. Reactions between acids and metal oxides.
    3. Reactions between acids and metal carbonates.
    4. Reactions between acids and metal hydrogen carbonates.
  • Reaction types 1 and 2 produce a salt and water.
    Reaction types 3 and 4 produce a salt, water and carbon dioxide.
  • Acid-base reactions are also known as neutralisation reactions.

 
vinegar baking soda acid base reaction

Mixing vinegar (acetic acid) and baking soda (sodium hydrogen carbonate) is an acid-base reaction.

(Image: f2014vad, Adobe Stock)

 

Acids

  • Acids are substances that produce hydrogen ions (H+) in solution.
  • The formation of acid solutions can be shown by the following generalised formula:

 
acid ionisation general formula

    Examples
    Hydrochloric acid:  HCl    H+  +  Cl
    Nitric acid:  HNO3    H+  +  NO3
    Acetic acid:  CH3COOH    H+  +  CH3COO

 

Bases

  • Bases are substances that produce hydroxide ions (OH) in solution.
  • They are ionic compounds, where the negative ion is one of the following:
    • Hydroxide (OH)
    • Oxide (O2–)
    • Carbonate (CO32–)
    • Hydrogen carbonate (HCO3)
  • The formation of base solutions from hydroxides can be shown by the following generalised formula:

 
base ionisation general formula

    Example
    Sodium hydroxide:  NaOH    Na+  +  OH
  • The formation of base solutions from oxides, carbonates and hydrogen carbonates is more complex, but result from reactions between these substances and water.
    Examples
    Sodium oxide:  Na2O  +  H2O    Na+  +  OH
    Sodium carbonate:  Na2CO3  +  H2O    H2CO3  +  Na+  +  OH
    Sodium hydrogen carbonate:  NaHCO3  +  H2O    H2CO3  +  Na+  +  OH

 

Neutralisation Reactions

  • Chemical reactions between acids and bases are known as neutralisation reactions.
    This is because, if they are mixed in equivalent proportions, there will be an equal amount of hydrogen ions and hydroxide ions, and therefore the resulting solution will be neutral. (Sometimes the products of the reaction react with the water, resulting in a solution that is acidic or basic).
  • Neutralisation reactions result in the formation of ionic compounds known as salts.
    Examples of salts include sodium chloride (NaCl), magnesium sulfate (MgSO4) and potassium acetate (KCH3COO).
  • Depending on the type of base, neutralisation reactions will also produce water, or both water and carbon dioxide.

 
nitric acid strontium carbonate base reaction

The reaction between nitric acid and strontium carbonate as an example of a neutralisation reaction.

(Image: LoyalSoldier, Wikimedia Commons)

 

Determining the Type of Salt Produced in Acid-Base Reactions

  • The type of salt produced in acid-base reactions depends on both the acid and the base.

 

The Positive Ion

  • The positive ion of the salt produced in acid-base reactions is determined by the positive ion of the base.
    Example
    Magnesium hydroxide, magnesium oxide, magnesium carbonate and magnesium hydrogen carbonate will all form magnesium salts when reacting with acids.

 
acid base salt positive ion

The positive ion of the salt produced in acid-base reactions is determined by the base.

 

The Negative Ion

  • The negative ion of the salt produced in acid-base reactions is determined by the negative ion of the acid.
    Examples
    Hydrochloric acid forms chloride salts.
    Sulfuric acid forms sulfate salts.
    Nitric acid forms nitrate salts.
    Acetic acid forms acetate salts.

 
acid base salt negative ion

The negative ion of the salt produced in acid-base reactions is determined by the acid.

 

Ammonium Salts

  • The ammonium ion (NH4+) is a bit unique. It is a polyatomic ion with a positive charge.
    Ammonium can form the positive ion in bases and salts.
    Therefore, the four types of acid-base reactions described below could have ammonia as the positive ion, rather than a metal.
    Example
    HCl  +  NH4OH    NH4Cl  +  H2O

 

Reactions Between Acids and Metal Hydroxides

  • The generalised equation for the reaction between acids and metal hydroxides is:

 
acid base metal hydroxide reactions formula equation

 

Reactions Between Acids and Metal Oxides

  • The generalised equation for the reaction between acids and metal oxides is:

 
acid base metal oxide reactions formula equation

 

Reactions Between Acids and Metal Carbonates

  • The generalised equation for the reaction between acids and metal carbonates is:

 
acid base metal carbonate reactions formula equation

 

Reactions Between Acids and Metal Hydrogen Carbonates

  • The generalised equation for the reaction between acids and metal hydrogen carbonates is:

 
acid base metal hydrogen carbonate reactions formula equation

 

Summary

  • Chemical reactions between acids and bases are known as neutralisation reactions.
  • Neutralisation reactions result in the formation of ionic compounds known as salts.
    Depending on the type of base, neutralisation reactions will also produce water, or both water and carbon dioxide.
  • There are four main types of acid-base reactions, depending on the type of base and the products formed.
    1. Reactions between acids and metal hydroxides:
    2. Acid  +  Metal Hydroxide    Salt  +  Water

    3. Reactions between acids and metal oxides:
    4. Acid  +  Metal Oxide    Salt  +  Water

    5. Reactions between acids and metal carbonates:
    6. Acid  +  Metal Carbonate    Salt  +  Water  +  Carbon Dioxide

    7. Reactions between acids and metal hydrogen carbonates:
    8. Acid  +  Metal Hydrogen Carbonate    Salt  +  Water  +  Carbon Dioxide

 
acetic acid sodium hydrogen carbonate base reaction

(Image: katerha, Wikimedia Commons)

 

(Header image: Alessandro e Damiano, Wikimedia Commons)

 

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