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B2.3 · Investigate element reactions and develop an activity series

Learn to investigate element reactions and develop an activity series through clear examples and targeted practice.

Ontario Grade 11 Chemistry

Matter, Chemical Trends, and Chemical Bonding

Ontario Grade 11 Chemistry • B2.3

A clean piece of zinc placed in a copper(II) solution may develop a reddish-brown coating while the blue colour of the solution fades. These visible changes are clues that substances have changed. By comparing how different elements react under similar conditions, chemists can arrange them by relative activity. This lesson focuses on investigating reactions and using the evidence to build and apply an activity series.

What you will learn

Describe observable evidence that can show a chemical reaction has occurred.
Use displacement reactions to compare the relative activity of metals.
Organize comparison results into an activity series and use it to predict a reaction.

1. From visible evidence to a reaction model

A chemical reaction makes one or more new substances. Observable clues can include a colour change, a solid forming, bubbles, or a change in the appearance of a metal. A clue is evidence to consider, not proof on its own. Compare the materials before and after the test, and use more than one observation when possible.

First review two terms. An element is a substance made of one kind of atom. An ion is an atom or group of atoms with an electric charge. In a metal salt solution, the metal is often present as positive ions. For example, copper(II) ions have a charge of

2+

. The Roman numeral in the name identifies the charge of the metal ion.

In a metal displacement reaction, a more active metal can replace a less active metal in a compound. At the particle level, atoms of the added metal take the place of metal ions in the solution. The displaced metal may appear as a solid coating or particles. The solution may also change colour as its dissolved ions change.

A familiar example is zinc placed in copper(II) sulfate solution. A coating of copper may form on the zinc, and the blue solution may become less intense. The balanced equation represents the change in substances and shows that atoms are conserved. State symbols identify whether a substance is solid, dissolved in water, or liquid.

\mathrm{Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s)}

Record observations before assigning a cause.
In a displacement reaction, one metal replaces another metal in a compound.
A balanced equation has the same number of each type of atom on both sides.

2. Compare metals fairly

To compare metals, test each one against the same set of metal-ion solutions. A solution contains a substance dissolved in water. For example, a copper(II) sulfate solution contains copper(II) ions. If the tested metal replaces copper, record a reaction. If there is no visible evidence of replacement, record no observed reaction under those test conditions.

A fair comparison changes only the metal being tested. Keep the solution type and amount, the size or exposed surface of each metal sample, the temperature, and the observation time as similar as practical. Use clean samples and avoid carrying solution from one test into another. Follow teacher instructions for handling and disposal; some metal solutions can be harmful.

Plan a results table with the tested metal as a row and each metal-ion solution as a column. Mark a positive result only when the evidence supports displacement. Include the actual observations, such as a new coating or a colour change, rather than recording only a yes or no. Do not treat an absence of visible change as proof that no reaction could occur in any other condition.

The results allow comparisons. If metal A replaces ions of metal B, A is more active than B in this type of reaction. If B does not replace ions of A, that is consistent with the same ordering. Repeated comparisons can establish a relative order without requiring every metal to be tested against every other metal.

Change one factor at a time to make comparisons meaningful.
A positive displacement result places the added metal above the displaced metal in activity.
Record observations and test conditions so results can be interpreted.

3. Arrange and use an activity series

An activity series is an ordered list of elements, usually metals in this context, from more active to less active. It summarizes comparisons from reactions. A course reference table may include metals that were not part of a particular investigation. Keep the scope clear: conclusions from your tests apply to the elements and conditions you tested, while the full course series comes from the reference table.

For example, a course-level series commonly places magnesium above zinc, zinc above iron, and iron above copper. This means magnesium can displace zinc, iron, or copper ions in suitable solutions; zinc can displace iron or copper ions; and iron can displace copper ions. Copper does not displace ions of the metals placed above it. The series predicts whether a displacement reaction is expected; it does not by itself describe how quickly a reaction happens.

To predict a reaction, identify the metal added and the metal ion in the solution. Compare their positions in the activity series. If the added metal is higher, predict displacement and write the products. If it is lower, predict no displacement. Then check that the formulas are correct, balance the equation, and add state symbols when they are known.

In ionic form, a displacement equation can show just the particles that change. This is a net ionic equation. For example, sulfate ions remain unchanged in the zinc and copper(II) sulfate reaction, so the net ionic equation leaves them out. Use the full formula equation when the question asks for all reactants and products.

\mathrm{Zn(s) + Cu^{2+}(aq) \rightarrow Zn^{2+}(aq) + Cu(s)}

Higher in the series means more active relative to metals below it.
A metal below another metal does not displace that metal from its ions.
Use the activity series as a prediction tool, then verify atom counts and charges.

4. Build conclusions carefully

A useful investigation combines a clear question, controlled comparisons, careful observations, and a conclusion supported by the pattern of results. For example, ask which of several metals can displace copper from copper(II) ions. Testing each metal in copper(II) solution can sort the tested metals into those that displace copper and those that do not. Further tests with other metal-ion solutions can establish more relationships.

When results seem inconsistent, first check the procedure and evidence. A metal may have a coating that hides its surface, a sample may be contaminated, or the observation may be difficult to see. Repeat a comparison when appropriate and report uncertainty honestly. Do not change the activity order simply to fit one unclear observation.

The activity series is relative: it compares elements with one another. A conclusion such as “zinc is more active than copper” is supported when zinc displaces copper from its ions. It does not mean that every possible test involving zinc and copper must look identical. Use the specific reaction evidence and the course table together.

Support each ordering claim with a displacement comparison or a course reference table.
Separate an observation from an interpretation.
Repeat or review unclear tests instead of overstating a conclusion.

Example comparison pattern

Comparison	Observation	Conclusion
Zinc in copper(II) solution	Copper coating forms	Zinc is more active than copper
Iron in copper(II) solution	Copper coating forms	Iron is more active than copper
Zinc in iron(II) solution	Iron coating forms	Zinc is more active than iron

Worked example

Use a set of observations to order three metals

In a classroom investigation, the recorded results show that zinc forms a copper coating in copper(II) solution, iron also forms a copper coating in copper(II) solution, and zinc forms an iron coating in iron(II) solution. Treat these as supplied observations, not as results from a new experiment. What relative order do they support for zinc, iron, and copper? Write the reaction for zinc in iron(II) solution.

Translate the first observations
Zinc and iron each displace copper from copper(II) ions. Each is therefore more active than copper in these comparisons.
$\mathrm{Zn > Cu,\quad Fe > Cu}$
Use the direct comparison
Zinc forms iron in the iron(II) solution. This means zinc replaces iron, so zinc is more active than iron.
$\mathrm{Zn > Fe}$
Combine the comparisons
Together, the evidence supports zinc above iron and iron above copper. The order is relative to these three tested metals.
$\mathrm{Zn > Fe > Cu}$
Write and balance the reaction
Zinc replaces iron in iron(II) chloride solution. One zinc atom and one iron atom appear on each side, and the two chloride ions are balanced. State symbols show the solid metals and dissolved compound.
$\mathrm{Zn(s) + FeCl_2(aq) \rightarrow ZnCl_2(aq) + Fe(s)}$

Answer: The supported order is zinc, then iron, then copper, from more active to less active. Zinc displaces iron from iron(II) chloride solution.

Check: Count the atoms: each side contains one zinc atom, one iron atom, and two chlorine atoms. The equation is balanced. The order follows the observed replacements.

Common mistakes and how to avoid them

Assuming every metal placed in a solution will displace its metal ions.

Correction: Compare the added metal with the dissolved metal in the activity series. Displacement is predicted only when the added metal is higher.

Treating a colour change alone as a complete explanation.

Correction: Record what changed, then connect the evidence to the substances and particles that could explain it.

Changing a formula subscript to balance an equation.

Correction: Keep each chemical formula intact. Balance by changing coefficients, and check that atoms are conserved.

Claiming a complete activity series from one comparison.

Correction: One comparison establishes only a relative order for the two metals. Use additional comparisons or the course reference table for a longer order.

Lesson summary

Displacement reactions provide evidence for comparing the relative activity of metals.
A metal that displaces another metal from its ions is higher in the activity series.
Controlled tests and careful observations support a reliable ordering.
Use the series to predict displacement, then write correct formulas and balanced equations.

Check your understanding

Question 1

A metal higher than copper is placed in a suitable copper(II) solution. What does the activity series predict?

It can displace copper from the solution.
Copper must displace the added metal.
No displacement is possible for any metal.
The solution must become a pure element.

Show answer and explanation

It can displace copper from the solution.

A metal higher in the activity series can displace a metal below it from that metal's ions.

Question 2

The results show that metal X displaces metal Y from Y ions. Which conclusion is supported?

Y is more active than X.
X is more active than Y.
X and Y have equal activity.
The result gives no comparison.

Show answer and explanation

X is more active than Y.

Displacing Y from its ions places X above Y in the relative activity order.

Question 3

Why should metal samples be tested under similar conditions?

So the metal is the only planned change between comparisons.
So every test produces a reaction.
So state symbols can be removed from equations.
So the activity series does not need observations.

Show answer and explanation

So the metal is the only planned change between comparisons.

Keeping other conditions similar makes it easier to attribute different results to the metal being tested.

Key terms

Activity series: An ordered list that compares elements by their relative ability to react in specified comparisons.
Displacement reaction: A reaction in which a more active element replaces a less active element in a compound.
Ion: An atom or group of atoms with an electric charge.
State symbol: A symbol after a formula that shows whether a substance is solid, liquid, gas, or dissolved in water.
Net ionic equation: An equation that shows the particles that change in a reaction and leaves out ions that remain unchanged.

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About this lesson and its review

Published by DoAssignment. This AI-assisted lesson follows Ontario Grade 11 Chemistry (SCH3U), expectation B2.3. It is a study resource, not an official curriculum publication.

Before publication, the draft is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability, and then requires administrator approval. Errors can still occur, so corrections are welcomed.

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