Chapter 3 · Question 7

What is the reactivity series? List the metals in decreasing order of reactivity from potassium to gold. State the significance of the position of hydrogen in the series and give one practical application of the reactivity series.

Answer Revealed

Direct Answer:

The reactivity series is a list of metals arranged in decreasing order of their reactivity, established through displacement experiments and reactions with oxygen, water, and acids. The series (most to least reactive): K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au. Hydrogen is included in the series as a reference because metals above hydrogen can displace it from dilute acids (producing H₂ gas), while metals below hydrogen cannot. Practical application: the extraction method for a metal is chosen based on its position in the series — highly reactive metals (K, Na, Ca, Mg, Al) need electrolytic reduction; moderately reactive metals (Zn, Fe, Pb, Cu) are reduced using carbon; least reactive metals (Ag, Au) are found in the free state.

Simple Explanation

The reactivity series is like a class ranking — it lists metals from the most reactive to the least reactive. Potassium is at the top (it explodes in water), gold is at the bottom (it just sits there unchanged). Hydrogen gets an honorary spot in the middle — metals above it can push hydrogen out of acids to make H₂ gas; metals below it cannot. This ranking is incredibly useful: it tells us which metals can displace others, predicts whether a reaction will happen, and even decides how we extract a metal from its ore.

Exam-Ready Structure

The reactivity series is the central organising concept of NCERT Class 10 Chapter 3, unifying the chemical properties of metals studied in Sections 3.2.1 to 3.2.4. 1. Definition: The reactivity series is a list of common metals arranged in the order of their decreasing reactivity (activity). It is based on experimental evidence from displacement reactions and reactions with oxygen, water, and dilute acids (Activities 3.9–3.12 and Activity 1.9 from Chapter 1). 2. The series (Table 3.2): Potassium (K) — most reactive, followed by Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminium (Al), Zinc (Zn), Iron (Fe), Lead (Pb), [Hydrogen (H)], Copper (Cu), Mercury (Hg), Silver (Ag), Gold (Au) — least reactive. 3. Position and significance of hydrogen: Hydrogen is the only non-metal in the series and serves as the critical dividing line. (a) Metals above hydrogen can displace hydrogen from dilute acids to produce H₂ gas. (b) Metals below hydrogen cannot displace hydrogen from dilute acids and do not react with them. 4. Practical applications: (a) Predicting displacement: A metal higher in the series can displace a lower metal from its salt solution. Example: Zn + CuSO₄ → ZnSO₄ + Cu, but Cu + ZnSO₄ → no reaction. (b) Extraction method selection: Highly reactive metals (K to Al) require electrolytic reduction of molten compounds. Moderately reactive metals (Zn to Cu) are extracted by reduction with carbon (coke). Low-reactivity metals (Hg, Ag, Au) can be obtained by heating their oxides alone or are found native. (c) Corrosion susceptibility: More reactive metals corrode more readily — this is why zinc is used to galvanise (protect) iron.

Key Points

Reactivity series (decreasing): K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au
Series is based on displacement experiments and reactions with oxygen, water, and acids
Hydrogen divides the series: metals above it displace H₂ from acids; metals below it do not
More reactive metal displaces a less reactive metal from its salt solution
Extraction method depends on position: electrolytic reduction (top), carbon reduction (middle), heating/found native (bottom)

What is the reactivity series? List the metals in decreasing order of reactivity from potassium to gold. State the significance of the position of hydrogen in the series and give one practical application of the reactivity series.