Reactivity of Metals: Activity Series, Displacement Reactions, and Redox Equations - Lab 6

Reactivity of Metals and the Activity Series

Introduction to Metal Reactivity

The reactivity of metals is a fundamental concept in general chemistry, describing how readily a metal will undergo chemical reactions, particularly with acids and salt solutions. This property is closely related to a metal's tendency to lose electrons and form positive ions (cations). The activity series is a ranking of metals based on their reactivity, which helps predict the outcomes of displacement reactions and redox processes.

• Active metals (e.g., Li, K, Ca, Na, Mg, Al, Zn) react readily with acids and can displace less reactive metals from solutions.

• Less active metals (e.g., Cu, Ag, Au) are less likely to react with acids or displace other metals.

Example of activity series (from most to least reactive):

• Li > K > Ba > Ca > Na > Mg > Al > Mn > Zn > Cr > Fe > Co > Ni > Sn > Pb > (H) > Cu > Ag > Hg > Pt > Au

Additional info: The position of hydrogen in the series is important for predicting reactions with acids.

Displacement Reactions and Redox Chemistry

Single Displacement (Replacement) Reactions

In a single displacement reaction, a more reactive metal displaces a less reactive metal from its compound in solution. These reactions are also redox reactions, involving the transfer of electrons.

• General form: Metal A + Salt of Metal B → Salt of Metal A + Metal B

• Example: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

Redox aspect: The more reactive metal is oxidized (loses electrons), and the less reactive metal ion is reduced (gains electrons).

Reactions of Metals with Acids

Many metals react with acids to produce hydrogen gas and a salt. The ability of a metal to do this depends on its position relative to hydrogen in the activity series.

• General equation: Metal + Acid → Salt + H2(g)

• Example: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

• Metals above hydrogen in the activity series will react with acids; those below will not.

Writing Molecular, Ionic, and Net Ionic Equations

• Molecular equation: Shows all reactants and products as compounds.

• Ionic equation: Shows all strong electrolytes as ions.

• Net ionic equation: Shows only the species that actually change during the reaction.

Example:

• Molecular: Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

• Ionic: Zn(s) + 2H+(aq) + 2Cl-(aq) → Zn2+(aq) + 2Cl-(aq) + H2(g)

• Net ionic: Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)

Laboratory Investigation: Activity Series of Metals

Purpose and Learning Goals

• To observe reactions of metals with acids and salt solutions using the activity series.

• To write and balance single replacement reactions using the activity series.

• To write ionic and net ionic equations for observed reactions.

Experimental Procedure Overview

1. Reactivity with Hydrochloric Acid (HCl): Test metals such as Ca, Mg, Fe, Cu, Zn, Sn, and Al with HCl and observe for gas evolution or dissolution.

2. Reactivity with Aqueous Salt Solutions: Test each metal with solutions of other metal salts (e.g., Ca(NO3)2, Mg(NO3)2, Fe(NO3)3, etc.) and observe for color changes, precipitate formation, or metal deposition.

3. Record observations in data tables and use results to build an activity series.

Sample Data Table: Reactivity of Metals with HCl

Metal	Observation with HCl	Reactions (molecular, ionic, net-ionic)
Al	Yes, slowly; gas evolved	Molecular: $2Al_{(s)} + 6HCl_{(aq)} \rightarrow 3H_2_{(g)} + 2AlCl_3_{(aq)}$ Ionic: $2Al_{(s)} + 6H^+_{(aq)} + 6Cl^-_{(aq)} \rightarrow 3H_2_{(g)} + 2Al^{3+}_{(aq)} + 6Cl^-_{(aq)}$ Net ionic: $2Al_{(s)} + 6H^+_{(aq)} \rightarrow 2Al^{3+}_{(aq)} + 3H_2_{(g)}$
Ca	[To be observed]	[To be written based on observation]
Mg	[To be observed]	[To be written based on observation]
Fe	[To be observed]	[To be written based on observation]
Cu	[To be observed]	[To be written based on observation]
Zn	[To be observed]	[To be written based on observation]
Sn	[To be observed]	[To be written based on observation]

Additional info: Students are expected to fill in the table based on their experimental results.

Sample Data Table: Reactivity of Metals with Metal Salt Solutions

Metals	Ca2+ as Ca(NO3)2	Mg2+ as Mg(NO3)2	Fe3+ as Fe(NO3)3	Cu2+ as Cu(NO3)2	Zn2+ as Zn(NO3)2	Sn2+ as SnCl2	Al3+ as Al(NO3)3
Ca							Yes, Ca dissolves
Mg							Yes, Mg dissolves
Fe							N.R.
Cu							N.R.
Zn
Sn
Al	N.R.	N.R.	Yes, turns aluminum dark	Yes, aluminum turns brown	Yes, aluminum turns dark	Yes, aluminum turns dark; solution colorless

Additional info: N.R. = No Reaction. Students are to complete the table based on their observations.

Balancing Redox Equations

Steps for Balancing Redox Equations

1. Write the unbalanced equation.

2. Assign oxidation numbers to all elements.

3. Identify the species being oxidized and reduced.

4. Write half-reactions for oxidation and reduction.

5. Balance atoms and charges in each half-reaction.

6. Combine the half-reactions and balance the overall equation.

Example:

• Unbalanced: $2Fe_{(s)} + 3Cl_2_{(g)} \rightarrow 2FeCl_3_{(s)}$

• Oxidation: $Fe^0 \rightarrow Fe^{3+} + 3e^-$

• Reduction: $Cl_2^0 + 2e^- \rightarrow 2Cl^-$

• Balanced: $2Fe_{(s)} + 3Cl_2_{(g)} \rightarrow 2FeCl_3_{(s)}$

Safety and Laboratory Practice

• Wear appropriate personal protective equipment (PPE) such as goggles and gloves.

• Handle acids and reactive metals with care; some reactions may be vigorous or produce hazardous gases.

• Work in a fume hood when required (e.g., with aluminum and HCl).

• Dispose of chemicals according to your instructor's guidelines.

Summary Table: Key Concepts

Term	Definition	Example
Activity Series	A list of metals ranked by their reactivity	Zn is above Cu, so Zn can displace Cu from CuSO4
Displacement Reaction	A reaction where a more reactive metal replaces a less reactive metal in a compound	Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
Redox Reaction	A reaction involving the transfer of electrons	Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Net Ionic Equation	An equation showing only the species that change during the reaction	Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

Practice and Application

• Predict whether a reaction will occur using the activity series.

• Write balanced molecular, ionic, and net ionic equations for single displacement reactions.

• Identify oxidized and reduced species, as well as oxidizing and reducing agents, in redox reactions.

Example Practice Questions

1. Will Zn react with HCl? Write the molecular and net ionic equations.

2. Will Cu react with Mg(NO3)2? Explain using the activity series.

3. For the reaction: $2Fe_{(s)} + 3Cl_2_{(g)} \rightarrow 2FeCl_3_{(s)}$, identify the oxidized and reduced species, and the oxidizing and reducing agents.

Additional info: These notes are based on a laboratory activity and are intended to help students understand and apply the concepts of metal reactivity, the activity series, and redox reactions in general chemistry.