Metal reactivity and displacementIB MYP Chemistry: Revision notes
Section 1
The reactivity series
The reactivity series ranks metals from most to least reactive:
Potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), aluminium (Al), (carbon), zinc (Zn), iron (Fe), (hydrogen), copper (Cu), silver (Ag), gold (Au)
Carbon and hydrogen are non-metals, but they are included for comparison. The more reactive a metal, the more easily it loses electrons to form positive ions, and the faster it reacts.
Learn the order with a mnemonic of your own. It must start K, Na, Ca, Mg, Al and end Cu, Ag, Au.
Section 2
Reactions with water, steam and oxygen
- Cold water: potassium, sodium and calcium react to give a metal hydroxide and hydrogen. For example: calcium + water → calcium hydroxide + hydrogen. Potassium is the most vigorous and burns with a lilac flame.
- Steam: magnesium, zinc and iron react with steam to give a metal oxide and hydrogen. For example: magnesium + steam → magnesium oxide + hydrogen.
- Oxygen: most metals form metal oxides when heated in air or oxygen. Magnesium burns with a bright white flame. Copper turns black (copper(II) oxide). Gold does not react.
Metals below hydrogen (copper, silver, gold) do not react with water or steam.
Test for hydrogen: a lit splint gives a squeaky pop.
Hydrogen is tested with a lit splint (squeaky pop). A glowing splint relighting is the test for oxygen.
Section 3
Reactions with dilute acid
Metals above hydrogen react with dilute acid:
metal + acid → salt + hydrogen
Example: Mg + 2HCl → MgCl₂ + H₂
The faster the bubbles of hydrogen, the more reactive the metal: magnesium is rapid, zinc steady and iron slow. Copper does not react because it is below hydrogen in the series. Potassium, sodium and calcium are too dangerous to react with acid in school.
You can place metals in order of reactivity by comparing how quickly bubbles form with acid.
Section 4
Displacement reactions
A more reactive metal displaces a less reactive metal from a solution of its compound.
Example: Zn + CuSO₄ → ZnSO₄ + Cu. The blue solution fades and pink-brown copper forms.
In terms of electrons, this is redox: zinc atoms lose electrons (Zn → Zn²⁺ + 2e⁻, oxidation) and copper ions gain them (Cu²⁺ + 2e⁻ → Cu, reduction). The more reactive metal is the reducing agent.
If the metal is less reactive than the one in the compound, there is no reaction, for example copper in zinc sulfate solution.
A displacement reaction only happens if the added metal is MORE reactive than the metal in the solution.
Section 5
Predicting reactions from the series
Use the position in the series to predict:
- Will the metal react with water, steam or dilute acid? Only if it is above the substance in the series (for acid, above hydrogen).
- Will metal X displace metal Y? Yes if X is above Y.
- How vigorous will it be? The further apart the metals, the more vigorous the reaction and the bigger the temperature rise.
Example: iron + copper(II) sulfate → iron(II) sulfate + copper (iron is above copper). Silver + copper(II) sulfate gives no reaction.
Write the two metals in order from the series first, then decide.
Must know
- Series: K, Na, Ca, Mg, Al, (C), Zn, Fe, (H), Cu, Ag, Au
- Metal + water → hydroxide + hydrogen (K, Na, Ca); metal + steam → oxide + hydrogen (Mg, Zn, Fe)
- Metal + dilute acid → salt + hydrogen (metals above hydrogen only)
- A more reactive metal displaces a less reactive one: the reaction is redox
- Test for hydrogen: lit splint, squeaky pop
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Metal reactivity and displacement
- A teacher in Doha demonstrates the reactions of metals with cold water. She adds small pieces of potassium, calcium and copper to separate troughs of water. The potassium moves across the surface and burns with a lilac flame, the calcium fizzes steadily and the copper does not react.Write the word equation for the reaction of calcium with water and state the test for the gas produced.2 marks
- A student in Dublin adds equal-sized pieces of magnesium, zinc, iron and copper to separate test tubes of dilute hydrochloric acid. Bubbles form rapidly with magnesium, steadily with zinc and slowly with iron, and there are no bubbles with copper.Write a balanced symbol equation for the reaction of magnesium with dilute hydrochloric acid.2 marks
- Students at a school in Seoul investigate displacement reactions. They add 1.0 g of magnesium powder, zinc powder or iron powder to 25 cm³ of copper(II) sulfate solution in a polystyrene cup with a lid, stir, and record the highest temperature reached. A pink-brown solid forms in each cup.State a hypothesis for the investigation, including a prediction of the order of the temperature rises, and give a scientific reason.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).