The reactivity series: water, steam and dilute acid
Use the exact required order and the named reactant conditions rather than one rule for every metal.
Section C9.4 · Reactivity series
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Distinguish magnesium's steam reaction from the cold-water hydroxide pattern.
- Predict chloride salts and hydrogen from a suitable metal with dilute HCl.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which point in the series helps predict hydrogen from dilute HCl?
What you will learn
- Recall the required reactivity order including carbon and hydrogen as comparison points.
- Explain the specified cold-water, steam and dilute-HCl reactions using that order.
Recall the full order, including non-metal reference points
From most to least reactive, the required sequence is potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold. Carbon and hydrogen are non-metal comparison points included in the series; their presence does not make them metals. Carbon's position helps with extraction choices, while hydrogen's position helps predict the stated dilute-acid reactions.
Magnesium, zinc and iron are above hydrogen and react with dilute hydrochloric acid to give hydrogen and chloride salts: MgCl₂, ZnCl₂ and FeCl₂ in these examples. Copper, silver and gold are below hydrogen and do not produce hydrogen from dilute HCl in this comparison. Do not extend this particular pattern to every acid: oxidising-acid reactions have different conditions and products.
Specify cold water or steam
Potassium, sodium and calcium react with cold water to form hydroxides and hydrogen under the stated supervised comparisons. Their reactivity order is K>Na>Ca. A balanced calcium example is Ca+2H₂O→Ca(OH)₂+H₂. Magnesium with steam gives MgO and H₂: Mg+H₂O(g)→MgO+H₂. Steam and cold-water product patterns must not be exchanged without considering the metal and conditions.
The position predicts relative chemical tendency, but the visible rate also depends on surface condition, exposed area, temperature and reactant concentration. Aluminium is relatively reactive but has a protective oxide layer, explained in the Extended lesson. A small observed rate is not proof that the metal belongs at the bottom of the series if its surface prevents contact. Reactive metal and steam comparisons are interpreted from supervised data, rather than performed as home trials.
Sources for this lesson
Pause and explain
Which statement describes magnesium with steam?
Worked example
Use the series to predict dilute-HCl behaviour of iron and copper, then give magnesium's steam products.
Show the worked solution
- Iron is above hydrogen and produces FeCl₂ and H₂: Fe+2HCl→FeCl₂+H₂.
- Copper is below hydrogen, so that hydrogen-producing dilute-HCl reaction is not predicted.
- Mg+H₂O(g)→MgO+H₂ gives the stated steam products.
Answer Iron gives FeCl₂ and H₂; copper does not give H₂ with dilute HCl; magnesium with steam gives MgO and H₂.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write the full required series and identify the two non-metal reference points.
Give me a hint
Include aluminium above carbon, and zinc and iron above hydrogen.
Compare my reasoning
- K, Na, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au is the descending order.
- C is carbon and H hydrogen, both non-metal reference points.
- Their positions support extraction and acid-reaction predictions without changing their classification.
K > Na > Ca > Mg > Al > C > Zn > Fe > H > Cu > Ag > Au; C and H are non-metals.
Look for these in your work
- Every required entry is present in order.
- The reference points are not called metals.
Predict the specified reactions for calcium with cold water, magnesium with steam and zinc with dilute HCl, then balance them.
Give me a hint
Each reactant condition has its own product pattern.
Compare my reasoning
- Ca+2H₂O→Ca(OH)₂+H₂ for cold water.
- Mg+H₂O(g)→MgO+H₂ for steam.
- Zn+2HCl→ZnCl₂+H₂ for dilute HCl.
Ca+2H₂O→Ca(OH)₂+H₂; Mg+H₂O(g)→MgO+H₂; Zn+2HCl→ZnCl₂+H₂.
Look for these in your work
- Conditions and products stay matched.
- All atom counts balance.
A report puts copper above zinc because its larger surface area gave a faster observation with a different acid. Explain why the comparison cannot overturn the specified series.
Give me a hint
Both apparatus conditions and the acid identity changed.
Compare my reasoning
- The specified series places zinc above copper.
- Different surface areas can alter rates, and a different acid can follow another chemical pattern.
- The observation does not isolate intrinsic reactivity under comparable specified conditions, so it cannot support the proposed reversal.
The confounded observation does not reverse Zn>Cu; compare the same stated conditions and relevant reaction pattern.
Look for these in your work
- Both changed conditions are identified.
- Rate evidence is not treated as an automatic series replacement.
Common mistakes
- Omitting carbon or hydrogen from the required order.
- Calling carbon and hydrogen metals because they appear in the series.
- Giving FeCl₃ as the stated iron/dilute-HCl product.
- Treating a surface-limited observation as an intrinsic rank.
What can you explain now?
Which of Mg, Zn, Fe, Cu, Ag and Au produce hydrogen with dilute HCl in the stated comparison?
Compare with the explanation
Mg, Zn and Fe; not Cu, Ag or Au.
The first three are above hydrogen in the required series, while the others are below it.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Recall the entire series, explain its carbon and hydrogen markers and predict the specified water, steam and HCl cases with balanced equations.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.