Metals Reactions

1. Reactivity Series of Metals

• Reactivity Order: Potassium > Sodium > Calcium > Magnesium > Aluminium > Carbon > Zinc > Iron > Hydrogen > Copper > Silver > Gold

• Key Trends:

  • The reactivity decreases down the series.

  • Highly reactive metals react vigorously, while less reactive metals show little or no reaction under similar conditions.

2. Reactions of Metals with Water

Cold Water:

• Metals like potassium (K), sodium (Na), and calcium (Ca) react vigorously with cold water.

• Products: Metal hydroxide and hydrogen gas.

• Examples:

  • Potassium:2K+2H2O→2KOH+H2 Observation: Potassium ignites with a lilac flame, forming bubbles of hydrogen gas.

  • Calcium:Ca+2H2O→Ca(OH)2+H2 Observation: Calcium reacts less vigorously, forming a cloudy solution (due to insoluble Ca(OH)₂).

Steam:

• Metals like magnesium react with steam to form metal oxides and hydrogen gas.

• Example:Mg+H2O (g)→MgO+H2(g) Observation: Bright white flame and white solid (magnesium oxide) forms.

No Reaction with Water:

• Metals lower in the reactivity series, such as zinc, iron, and copper, do not react with water under normal conditions.

3. Reactions of Metals with Acids

• Metals react with dilute acids (e.g., HCl, H₂SO₄) to produce a salt and hydrogen gas.

• Equation:Metal+Acid→Salt+H2

• Examples:

  • Magnesium and hydrochloric acid:Mg+2HCl→MgCl2+H2

  • Observation: Bubbles of hydrogen form rapidly; the reaction is exothermic.

  • Zinc and sulfuric acid:Zn+H2SO4→ZnSO4+H2Observation: Effervescence, moderate reaction speed.

  • Copper and hydrochloric acid:

    • No reaction occurs because copper is below hydrogen in the reactivity series.

Testing for Hydrogen:

• Collect the gas in a test tube and ignite with a lit splint. A ‘pop’ sound confirms the presence of hydrogen.

4. Reactions of Metals with Oxygen

• Metals react with oxygen to form metal oxides. The reactivity decreases down the series.

Highly Reactive Metals:

• Potassium:4K+O2→2K2O Observation: Vigorous reaction with a bright flame.

Moderately Reactive Metals:

• Magnesium:2Mg+O2→2MgO Observation: Intense white flame producing a white powder.

Unreactive Metals:

• Metals like copper react slowly, requiring heat:2Cu+O2→2CuO2Cu+O2​→2CuO Observation: Black copper(II) oxide forms.

5. Displacement Reactions

• A more reactive metal can displace a less reactive metal from its compound.

• Example:

  • Zinc displacing copper from copper(II) sulfate:Zn+CuSO4→ZnSO4+Cu Observation: Copper metal (reddish-brown) deposits, and the solution turns colorless.

6. Practical Observations and Trends

Tendency to Form Ions:

• Metals at the top of the reactivity series lose electrons more readily, forming positive ions quickly.

Barriers to Reactivity:

• Aluminium appears unreactive due to its oxide layer, which prevents further reaction:4Al+3O2→2Al2O34Al+3O2​→2Al2​O3​

Experimental Tests:

• Reaction Speed: The speed of reaction with acids or water increases with reactivity.

• Hydrogen Test: Confirm hydrogen gas with the “pop” test.

Summary Table