Learning Objective

In this lesson we will learn about chemical reactions between acids and metals.

Learning Outcomes

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

  • Predict whether a chemical reaction between an acid and a metal will take place or not.

  • Determine the products of chemical reactions between acids and metals.

  • Describe how the hydrogen pop test can be used to confirm that a chemical reaction between an acid and a metal has taken place.

 

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Introduction

  • Dilute acids react with most metals to form a salt and hydrogen.
  • The reactivity series of metals can be used to predict which metals will react with dilute acids.
  • A chemical reaction between an acid and a metal can be confirmed by conducting a hydrogen pop test.

 

Reactivity of Metals

  • Metals are elements that react by losing valence electrons to form positive ions.
    They then combine with negative ions to form ionic compounds.
    When formed during acid-metal reactions, these compounds are usually referred to as salts.
  • Since different metals require different amounts of energy to lose valence electrons, the chemical reactivity of metals varies.
    Generally, metals lose electrons easily, therefore most metals will react with acids.
    However, the less reactive metals will not react with acids.

 
acid metal reactivity

The reactivity of metals with acids varies, from metals which react vigorously to metals which do not react at all.

(Image: Amangeldyurazov, Wikimedia Commons)

 

Reactivity Series of Metals

  • The reactivities of common metals are listed from most reactive to least reactive in the reactivity series of metals.
  • Hydrogen is often included in this list as a way of determining which metals will react with acids.
    Metals above hydrogen on the reactivity series will react with dilute acids.
    Metals below hydrogen on the reactivity series will not react with dilute acids.
  • Examples of metals that do react with acids include lithium, aluminium, zinc and iron.
    Examples of metals that do not react with acids include copper, platinum and mercury.

 
reactivity series of metals acid reactions

The reactivity series of metals can be used to predict which metals will react with acids.

 

Reactions Between Acids and Metals

  • Acids react with metals to produce a salt and hydrogen.

 
acid metal reaction general formula equation

 

Determining the Type of Salt Produced in Acid-Metal Reactions

  • The type of salt produced in acid-metal reactions depends on both the acid and the metal.
    It is determined in a manner very similar to acid-base reactions.

 

The Positive Ion

  • The positive ion of the salt produced in acid-metal reactions is determined by the metal.
    Examples
    Sodium metal produces sodium salts.
    Magnesium metal produces magnesium salts.
    Aluminium metal produces aluminium salts.
    Zinc metal produces zinc salts.

 
acid metal reaction salt positive ion

The positive ion of the salt produced in an acid-metal reaction is determined by the metal.

 

The Negative Ion

  • The negative ion of the salt produced in acid-metal 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 metal reaction salt negative ion

The negative ion of the salt produced in an acid-metal reaction is determined by the acid.

 

Observing Acid-Metal Reactions

  • Since a chemical reaction between an acid and a metal will produce hydrogen gas, this can be used to determine whether a particular metal has reacted with an acid or not.
  • Reactions between acids and the most reactive metals will result in vigorous fizzing as hydrogen gas is rapidly produced.
    Reactions between acids and metals towards the middle of the reactivity series are less vigorous and result in a slow production of bubbles of hydrogen gas.

 

Testing for the Production of Hydrogen Gas

  • While fizzing or the slow appearance of bubbles will indicate the production of a gas and therefore that a chemical reaction has taken place, confirmation of the type of gas requires additional testing.
    The hydrogen pop test can be used to confirm that hydrogen gas has been produced.
    If a lit splint is placed inside a test tube containing hydrogen gas, there will be a “pop” sound.
    This is because the hydrogen gas, in the presence of a flame, reacts rapidly with oxygen to form water, with some of the energy produced converted to sound.

 
hydrogen gas pop test acid metal reactions

The hydrogen pop test can be used to confirm the production of hydrogen gas during an acid-metal reaction.

 

Summary

  • Acids react with most metals to form a salt and hydrogen, as shown by the following equation:
  • Acid  +  Metal    Salt  +  Hydrogen

  • Since the reactivity of different metals varies, some metals react vigorously with acids, some react slowly and some do not react at all.
  • The reactivity series of metals, which lists metals from most reactive to least reactive, can be used to predict which metals will react with acids.
    Metals above hydrogen on the reactivity series will react with dilute acids.
    Metals below hydrogen on the reactivity series will not react with dilute acids.
  • The hydrogen pop test can be used to confirm that a chemical reaction has taken place between an acid and a metal – a lit splint will “pop” if placed in the presence of hydrogen gas.

 

 acid metal etching engraving armour  acid metal decorative pattern

Acids have been used for hundreds of years to create etchings and decorative patterns in metal.

(Images: G. McFly, Wikimedia Commons; PublicDomianPictures)

 

(Header image: mulderphoto, Adobe Stock)

 

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