Unit A: Chemical Change

Lesson 2.3: The Reactivity of Metals



Figure 1:  Gold Roman coin by Kaly99
Both of these coins are about 2500 years old.  Metals react with oxygen over time and tarnish.  You can see the green tarnish on the copper coin best.

Different metals react at different rates.

Gold is quite nonreactive, while copper reacts quite readily.  Many other metals do not make good coins because they are far too reactive.

 

Copper Roman coin by Jerry "Woody"

  • Read pages 76 and 77 of the textbook. Think about the Practice questions 22 and 23 and check your answers below.   Define corrosion.

 

Science 20 Text.  Courtesy Alberta Education



Some metals are more reactive than others.  That explains why single replacement reactions take place. 
For example,  «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mn»3«/mn»«msub»«mi mathvariant=¨normal¨»K«/mi»«mrow»«mo»(«/mo»«mi mathvariant=¨normal¨»s«/mi»«mo»)«/mo»«/mrow»«/msub»«mo»§#160;«/mo»«mo»+«/mo»«mo»§#160;«/mo»«msub»«mi»AlCl«/mi»«mrow»«mn»3«/mn»«mo»§#160;«/mo»«mo»(«/mo»«mi»aq«/mi»«mo»)«/mo»«/mrow»«/msub»«/math» «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mo»§#8594;«/mo»«mo»§#160;«/mo»«mn»2«/mn»«msub»«mi»Al«/mi»«mrow»«mo»(«/mo»«mi mathvariant=¨normal¨»s«/mi»«mo»)«/mo»«/mrow»«/msub»«/math»+ «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mn»3«/mn»«msub»«mi»KCl«/mi»«mrow»«mo»(«/mo»«mi»aq«/mi»«mo»)«/mo»«/mrow»«/msub»«/math»  happens because potassium is more reactive than aluminium, so it reacts with chlorine.  If potassium was not more reactive then the reaction might not occur.  Many reaction could be predicted if the relative reactivity of metals was known.  One way to compare the reactivity of metals is to set up a competition.

  • Read “Investigating the Reactivity of Metals” at the bottom of page 77 of the textbook.

  Investigation: Ranking the Reactivity of Metal Ions

  • Read the entire investigation on page 78 of the textbook.

If you have access to a supervised laboratory, do Path 1. If you do not have access to a supervised laboratory, do Path 2. An understanding of this activity will help you answer important assessment questions.

  • Follow the directions of the investigation, and answer questions 1, 2 and 4.  Check your answers below.

 

Science 20 Text.  Courtesy Alberta Education

  • Use the sample data for this investigation in the answer in "Path 1" to complete analysis questions 1, 2 and 4.  Check your answers above.
In the previous investigation, you discovered that metals and metal ions vary in their reactivity with non-metals. Metals and their corresponding ions are arranged according to their reactivity in an activity series.
  • Read pages 79 to the practice questions.  Think about the practice questions and check your answers.
Corrosion has a huge cost to society.  Bridges, ships, building structures and automobile bodies all corrode quite easily.  A lot of money is spent trying to prevent, repair or replace damage due to corrosion.  Iron reacts with water very readily to form an iron ion.   If iron ion reacted readily, a chemical solution to corrosion would be found, but iron ion is very content in compound form (rust)  and is not easily converted back to iron.  Ions and their atoms react differently.


  • Read page 79 - 83 of the textbook.   Watch the video on the right to review what you have learned so far, and preview what you are about to learn.

The activity series helps predict whether reactions between metals will occur or not  (spontaneous and non-spontaneous reactions).  It is key to understanding reactions in electrochemical and electrolytic cells in the next chapter.  

  • Carefully read page 81- 82 and work through the examples.  Watch the video on the right  if you need more explanation.  Read the summary below, then make sure you do Practice questions 26 - 30, as they are crucial to understanding the next chapter and similar question will appear on the final exam.  Check your answers below.


The Reduction table will help you predict whether the reaction will be spontaneous or non-spontaneous.  It also help you identify the reduction and oxidation half reactions.  Follow these steps to use the table...
  • identify the atom and the ion
  • determine if these are 'step up'  or 'step down' reactions.  See figure 3 below.
  • look at the electrons to determine the oxidation half reaction and the reduction half reaction.

     
Figure 3:  Step up and step down reactions.  Stepping up requires energy, while stepping down requires no energy.  Science Data booklet.  Alberta Education.  Modified by ADLC

Self Check

Determine if the following reactions will be spontaneous or non-spontaneous.  Write the oxidation and reduction half reactions.
Mg is reacting with K+

This is a 'step up' reaction so it is non-spontaneous.
Mg loses electrons so the oxidation half reaction is:
    «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mi»Mg«/mi»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#8594;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«msup»«mi»Mg«/mi»«mrow»«mn»2«/mn»«mo»+«/mo»«/mrow»«/msup»«/math» +  «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mn»2«/mn»«msup»«mi mathvariant=¨normal¨»e«/mi»«mo»-«/mo»«/msup»«/math»
K+ gains electrons, so the reduction half reaction is:
    «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi mathvariant=¨normal¨»K«/mi»«mo»+«/mo»«/msup»«/math» +  «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi mathvariant=¨normal¨»e«/mi»«mo»-«/mo»«/msup»«/math» «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mo»§#8594;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«mi mathvariant=¨normal¨»K«/mi»«/math»
«math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi»Cr«/mi»«mrow»«mn»3«/mn»«mo»+«/mo»«/mrow»«/msup»«/math» reacts with Na

This is a 'step down' reaction, so it is spontaneous.
Na loses electrons, so the oxidation half reaction is:           «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mi»Na«/mi»«mo»§#160;«/mo»«mo»§#8594;«/mo»«mo»§#160;«/mo»«msup»«mi»Na«/mi»«mo»+«/mo»«/msup»«mo»§#160;«/mo»«mo»+«/mo»«mo»§#160;«/mo»«mn»1«/mn»«msup»«mi mathvariant=¨normal¨»e«/mi»«mo»-«/mo»«/msup»«/math»
Cr3+ gains 3 electrons, so the reduction half reaction is:    «math class=¨wrs_chemistry¨ xmlns=¨http://www.w3.org/1998/Math/MathML¨»«msup»«mi»Cr«/mi»«mrow»«mn»3«/mn»«mo»+«/mo»«/mrow»«/msup»«mo»§#160;«/mo»«mo»+«/mo»«mo»§#160;«/mo»«mn»3«/mn»«msup»«mi mathvariant=¨normal¨»e«/mi»«mo»-«/mo»«/msup»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#8594;«/mo»«mo»§#160;«/mo»«mi»Cr«/mi»«/math»


This is a step sown reaction so it is spontaneous.
Na lost and electron to the oxidation half reaction is:
     «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mi»Na«/mi»«mo»§#160;«/mo»«mo»§#160;«/mo»«mo»§#8594;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«msup»«mi»Na«/mi»«mo»+«/mo»«/msup»«/math» «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mo»+«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«msup»«mi mathvariant=¨normal¨»e«/mi»«mo»-«/mo»«/msup»«/math»
«math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi»Cr«/mi»«mrow»«mn»3«/mn»«mo»+«/mo»«/mrow»«/msup»«/math»  gains electrons, so the reduction half reaction is:
     «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi»Cr«/mi»«mrow»«mn»3«/mn»«mo»+«/mo»«/mrow»«/msup»«/math» + 3«math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi mathvariant=¨normal¨»e«/mi»«mo»-«/mo»«/msup»«/math» «math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«mo»§#8594;«/mo»«mo»§#160;«/mo»«mo»§#160;«/mo»«mi»Cr«/mi»«/math»
  • Read page 83.  Define Reducing agent and oxidizing agent.  Do Practice questions # 31 - 32 and check your answers in below.

 

Science 20 Textbook.  Courtesy of Alberta Education


Try this
Various metals are reacted to test their relative reactivity.  The evidence is recorded on this table
I2 (aq)«math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi»Cu«/mi»«mrow»«mn»2«/mn»«mo»+«/mo»«/mrow»«/msup»«/math» (aq)Ag+ (aq)Br2 (aq)
«math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msub»«msup»«mi mathvariant=¨normal¨»I«/mi»«mo»-«/mo»«/msup»«mrow»«mo»(«/mo»«mi»aq«/mi»«mo»)«/mo»«/mrow»«/msub»«/math»xxreactedreacted
Cu(s)reactedxreactedreacted
Ag(s)xxxreacted
B«math xmlns=¨http://www.w3.org/1998/Math/MathML¨ class=¨wrs_chemistry¨»«msup»«mi mathvariant=¨normal¨»r«/mi»«mo»-«/mo»«/msup»«/math» (aq)xxxx

Use this evidence to list these substances from most reactive to least.  Click the video button on the right for the solution.


Kent True:  Reduction Table Building

The activity series was produced by performing experiments that test the position of various metals and their ions relative to one of the metals. In the next activity an experiment an experiment is designed to determine the position of metals above and below hydrogen.  Do this activity if you want to develop you ability to initiate and plan an experiment.

  Investigation: Planning an Experiment Using the Activity Series


  • Read the investigation on page 84 of the textbook. Follow the directions, and answer the questions.

    Check your answers with those in the “ Suggested Answers” in the online course.

Gold has been of great importance in the making of jewelry throughout history.  Now, gold is also valuable in manufacturing personal computers.

  • If you are interested, read “Gold—From Jewelry to High Technology” on page 84 of the textbook and “Did You Know?” on page 85.

  • Read “2.3 Summary” on page 85 of the textbook. Then, complete “2.3 Questions” # 2, 5 - 7. Check your answers below.

     

    Science 20 Textbook.  Courtesy Alberta Education


Go to Assignment 2.3: The Reactivity of Metals.