CHEMICAL PROPERTIES -METALS class X

 

             Reaction of Metals

CHEMICAL PROPERTIES OF METALS

  Revision Notes-class X Chemistry

 

1.Reaction of Metals with Oxygen

•  Metals react with oxygen to form metal oxides.  

METAL  +    O₂     →   METAL OXIDE

• The Intensity  of reaction with oxygen depends on the chemical reactivity of metal. Some metals react with oxygen even at room temperature, some react on heating, whereas still others react only on strong heating.

• Sodium and Potassium metal reacts with the oxygen of air at room temperature to form a basic oxide .

• Potassium and sodium metals are so reactive that they react vigorously with the oxygen . They catch fire and start burning when kept open in the air. 

        4Na (s)  + O₂ (g) →   2Na₂ O (s)  

           4K(s)  + O₂ (g) →   2K₂ O (s)  

• potassium metal and sodium metal are stored under kerosene oil to prevent their reaction with the oxygen, moisture and carbon dioxide of air.

• Magnesium metal does not react with oxygen at room temperature. But on heating, magnesium metal burns in air giving intense heat and light to form a basic oxide called magnesium oxide (which is white powder) :

         2Mg (s)   +   O₂ (g)    →   2MgO (s) 

• Aluminium metal burns in air, on heating, to form aluminium oxide : Al₂O₃

         Al  +  3O₂ (g)    →   2 Al₂O₃ (s) 

•  Zinc metal burns in air  on strong heating to form zinc oxide: 

          2 Zn (s)  +   O₂ (g)     →  2 ZnO (s)

• Iron reacts with the oxygen of air on heating to form iron (II, III) oxide:

         3Fe (s)    +  2O₂ (g)     →    FeO (s)  

• Copper reacts with the oxygen of air on prolonged heating to form a black substance coppes (II) oxide:

         2Cu (s)  +  O₂    →    2CuO (s) 

• Metal oxides are basic in nature.
• Some of the metal oxides react with water to form alkalis.
• Metal oxides, being basic, turn red litmus solution blue.

  2. Reaction with Water:

• Some metal react with water to form metal hydroxide and hydrogen gas.

Metal  +  Water  →  Metal hydroxide  + H₂

• Highly reactive  metal like Na, K, Ca  react with cold water and Magnesium  react with hot water.

• Sodium and potassium react violently with cold water. Hydrogen evolved in this reaction  catch fire because of reaction is highly exothermic.

2K (s) + 2 H₂O  (l)   →  2KOH (aq)  +  H₂ (g) +  Heat

2Na (s) + 2 H₂O  (l)   →  2NaOH (aq)  +  H₂ (g) +  Heat 

• Calcium react with cold water to form calcium hydroxide and hydrogen  .
• This reaction is less exothermic . so hydrogen evolved in this reaction does not catch fire.

Ca(s) + 2 H₂O  (l)   →  Ca(OH)₂ (aq)  +  H₂ (g) +  Heat

• Magnesium react with hot water to form Magnesium hydroxide and hydrogen.

Mg(s) + 2 H₂O  (l)   →  Mg(OH)₂ (aq)  +  H₂ (g)

• This reaction is not exothermic.

•  Less reactive metals like aluminium, zinc, iron etc neither react with cold water  nor hot water.

3. Reaction with Steam :

• Less reactive metals like Mg, Al , Fe, Zn  react with steam to form metal oxide and evolved hydrogen gas.

Metal  +  Steam (H₂O)  → Metal oxide + H₂ (g)

2Al  +  3H₂O (Steam) →  Al₂O₃ (s)  +  H₂ (g)

Zn  +  H₂O (Steam) →  ZnO(s)  +  H₂ (g)

3Fe  +  4H₂O (Steam) →  Fe₃O₄ (s)  +  4H₂ (g)

• Metal like Pb, Cu, Ag, Au, Pt do not react with either water or steam.

4. Reaction with Dilute Acid :

• Some metal react with dilute acid ( HCl, H₂SO₄ )  to form Salt and Hydrogen.

Metal  +  Acid   →   Metal salt  +  H₂ (g)

• Na, K , Ca  react Vigorously .
• Mg reacts moderately .
• Al, Zn, Fe  react slowly .
• Cu, Ag, Au , Pt  do not  react with acid because of these are less reactive metals and placed after hydrogen in reactivity series.

Reaction with Dilute Nitric acid:

• When metal react with dilute nitric acid , then hydrogen evolved in this reaction is oxidized into water rapidly . and Nitric acid get reduced into nitrogen oxide.

• To obtain hydrogen gas,  very dilute nitric acid is used .

• Very dilute nitric acid react with  Magnesium  and manganese only to form hydrogen gas.

Mg (s)  +  2 HNO₃  (aq)  →  Mg(NO₃)₂  +  H₂ (g)

Mn (s)  +  2 HNO₃  (aq)  →  Mn(NO₃)₂  +  H₂ (g)

5. Reaction with Salt solution :

• A more reactive metal displaces a less reactive metal from its salt solution and hence  reaction is occurred. This reaction is called displacement reaction.

Metal (A)  +  Salt solution of metal (B)→  Salt solution of metal (A)  + Metal B

Reaction occurs if,

• Metal ‘A’  is more reactive  than Metal ‘B’

CuSO₄ ( aq) + Zn (s)  →  ZnSO₄ ( aq)  +  Cu (s)  

• In this reaction blue solution of copper sulphate get turned colorless due to formation of zinc sulphate solution. and red brown copper is formed on zinc strip..

CuSO₄ ( aq) + Fe (s)  →  FeSO₄ ( aq)  +  Cu (s)  

•  In this reaction blue solution of copper sulphate get turned greenish  due to formation of Ferrous sulphate solution. and red brown copper is formed on iron strip.   

 

AgNO₃ (aq)  + Cu (s)  →  Cu(NO₃)₂  (aq)  +  2Ag (s)

•  In this reaction white solution of silver nitrate  get turned bluish  due to formation of copper nitrate  solution.

 6. Reaction with Chlorine :

• Highly Reactive metal react with chlorine at  room temperature to form ionic metal chloride.

2 K + Cl₂      →  2 KCl

2 Na + Cl₂    →  2 NaCl

Ca  + Cl₂      →    CaCl₂ 

• Less reactive metal react with chlorine on heating to form ionic metal chloride.

Mg  (s) +   Cl₂   (g)  →   MgCl₂  (s)

2Al (S)   +   3Cl₂ (g)   →  2AlCl₃ (s)

Zn (s)   +  Cl₂ (g)    →   ZnCl₂  (s)

2Fe (s)   +   3Cl₂ (g)   →  2FeCl₃ (s)

Cu (s)   +  Cl₂ (g)    →   CuCl₂  (s)

7. Reaction with Hydrogen :

• When hydrogen gas is passed over some heated  metal like  K, Na, Ca  and Mg   then metal hydride is formed.

2 K + H₂ (g)      →  2 KH (s)

 2 Na + H₂ (g)      →  2 NaH (s)

Ca  (s) +   H₂ (g)      →   CaH₂  (s)

Mg  (s) +   H₂ (g)      →   MgH₂  (s)

• Metal hydride is a ionic compound in which hydrogen exist as hydride ion (H^-1 ).

• Other metals do not react with hydrogen .

 Amphoteric oxides.

• some of the metal oxides show basic as well as acidic nature. Those metal oxides which show basic as well as acidic behavior are known as amphoteric oxides

• Aluminium metal and zinc metal form aluminium oxide and zinc oxide are amphoteric in nature.

• Amphoteric oxides react with both, acids as well as bases to form salts and water. 

• Aluminium oxide reacts with hydrochloric acid to form aluminium chloride (salt) and water: 

6HCI (aq)   +  Al₂ O₃→  2AICI₃ (s)  +   H₂O    

• Aluminium oxide reacts with sodium hydroxide to form sodium meta aluminate 

 2AI₂O₃ (aq)  +  2NaOH (aq)  + H₂O  → 2NaAIO₂  

• Zinc oxide reacts with hydrochloric acid to form zinc chloride (salt) and water:

ZnO (s)    +    2HCI (aq)   →   ZnCl₂      +   H₂O 

• Zine oxide reacts with sodium hydroxide to form sodium zincate (salt) and water: 

ZnO (s)   +  2NaOH (aq)       →   Na₂ ZnO₂   +H₂O (I)