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4 Chemical Properties

May 18, 2013

Introduction to 4 chemical properties:

We will study the chemical properties as exhibited by two important categories of elements, namely metals and non-metals.

Oxidation reaction:

Some metals like Na, K, and Ca combine readily with oxygen of air forming oxides that are basic in nature since the oxides dissolve in water to form alkali.

4Na  +  O2  → 2 Na2O

Na2O  + H2O  →  2 NaOH

Mg, Al and Zn also form basic oxides on heating in oxygen.  Ag, Au and Pt do not combine with oxygen even on heating.  These metals are termed noble metals.
On the other hand, some metals like copper, tin and chromium give oxides when heated at high temperature, while nickel get oxidized only at the surface even on strong heating.

Non-metals burn in oxygen forming acidic oxides since the oxides dissolve in water forming acids.

S  +  O2  →  SO2

SO2  + H2O  →  H2SO3

4 chemical properties : Reaction with water:

Some metals react with water at room temperature while the others react only with boiling water. A few metals react only when steam is passed over heated metal. For example, sodium, potassium and calcium are active metals and decompose water at room temperature giving hydrogen and hydroxides of the metal. Their reactions can be represented by the following chemical equations:

2Na + 2H2O → 2NaOH + H2

2K +2H2O →   2KOH + H2

Ca +2H2O →  Ca (OH)2 + H2

Magnesium, zinc and aluminum powder, on the other hand, decompose water giving hydrogen and oxide of the metal when reacted with boiling water.

Mg + H2O →  MgO +H2

Zn + H2O →  ZnO + H2

2Al + 3H2O → Al2O3 + H2

Iron is attacked by water at room temperature or at 100 deg C. However, heated iron reacts with steam to give hydrogen and magnetic oxide of iron (Fe3O4).

3Fe + 4 H2O → Fe3O4 + 4H2

4 chemical properties : Reaction with acids:

Dilute acids react with metals to liberate hydrogen and the corresponding salt of the metal. For example, zinc and magnesium react with sulfuric acid to yield hydrogen and zinc sulfate and hydrogen and magnesium sulfate, respectively, while with hydrochloric acid they give hydrogen and the corresponding chlorides.

Zn + H2SO4 →  ZnSO4 +H2

Mg + H2SO4 →  MgSO4 + H2

Mg + 2 HCl → MgCl2 +H2

Zn + 2 HCl → ZnCl2 +H2

Nitric acid, on the other hand, gives a series of salts with metals. For example, very dilute nitric acid reacts with magnesium and manganese to give hydrogen. In general, nitric acid gives oxides of nitrogen – nitrogen dioxide (NO2) and nitric oxide (NO) with common metals. For example, concentrated nitric acid gives nitrogen dioxide with copper or zinc.

Cu + 4HNO3 → Cu (NO3)2 + 2NO2 +2H2O

Zn + 4HNO3 →  Zn (NO3)2 +2NO2 +2H2O

4 chemical properties : Displacement of metals by other metals:

It has been observed that certain metals are capable of displacing other meatls from their solutions. It can be said, in general, more active metals displace less active metals from their salt solutions. For example,

a)    Iron and zinc displace copper from copper sulfate solution.

CuSO4 +Fe → FeSO4 + Cu

CuSO4 + Zn → ZnSO4 +Cu

b)    Zinc displaces lead from lead nitrate solution.

Pb (NO3)2 + Zn →   Zn (NO3)2 +Pb

c)    Copper displaces mercury form mercuric nitrate solution.

Cu + Hg (NO3)2 → Cu (NO3)2 + Hg

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