Chemical properties of Metals -
1. Reaction of metals with Oxygen (of air ) -
Metals react with oxygen to form metal oxides which are basic in nature and turn red litmus blue. The vigour reaction of oxygen depends upon the chemical reactivity of the metal.
i) Sodium and potassium metals react with oxygen at room temp. to form sodium oxide.
4Na + O2
2Na2O
- Sodium , potassium and lithium are very reactive so they catch fire and start burning when kept in open air. So they are stored in kerosene oil to prevent their reaction with the oxygen ,moisture and carbon dioxide of air.
- Most metal oxides are insoluble in water but some dissolve in water to form alkalies.
Sodium oxide and potassium oxide are soluble in water and from alkalies called sodium hydroxide (NaOH) and potassium hydroxide ( KOH).ii) Magnesium metal does not react with oxygen at room temp. On heating it gives intense heat and light to form a basic oxide (MgO- a white powder) Heat is required , so Mg is less reactive than Na or K.
iii) Aluminium metal - burns in air to form Al2O3
It is an amphoteric oxide ( which shows basic as well as acidic behavior and react with both acids as well as bases to form salts and water).
iv) Zinc metal burns in air only on strong heating to form zinc oxide . It is also an Amphoteric oxide.Al2O3 + 6HCl → 2 AlCl3 + 3H2O
Al2O3 + 2NaOH → 2NaAlO2 + H2O
v) Iron metal does not burn even on strong heating. It reacts with the oxygen of air on heating to form iron( II, III) oxide.ZnO + 2HCl → ZnCl2 + H2O
ZnO + 2NaOH → Na2ZnO2 + H2O
vi) Copper metal does not burn even on strong heating but reacts with oxygen of air to form a black substance copper (II) oxide.3Fe + 2O2 → Fe3O4
2Cu + O2 → 2CuO
2. Reaction of Metals with Water -
Metals react with water to form a metal hydroxide (or metal oxide) and hydrogen gas. Some metals react with cold water , some with hot water , some with steam and some do not react with steam also.
a) Reaction with Water ( hot or cold) – products formed are metal hydroxide and hydrogen gas.
Potassium and Calcium react with cold water
2K + 2H2O → 2KOH + H2 + Heat
It is highly exothermic reaction due to which hydrogen gas formed catches fire immediately. Potassium is a very reactive metal.
Magnesium reacts with hot water to form magnesium hydroxide and hydrogen. It starts floating due to the bubbles of hydrogen gas sticking to its surface.
Mg + 2H2O → Mg(OH)2 + H2
b) Reaction with steam - products are metal oxide and hydrogen gas. Magnesium reacts rapidly with steam to form magnesium oxide and hydrogen .
Mg + H2O → MgO + H2
Metals like aluminium, zinc, iron do not react with hot/cold water ; they react only with steam to form a metal oxide and hydrogen .
2Al + 3 H2O → Al2O3 + 3H2
Zn + H2O → ZnO + H2
3Fe + 4H2O → Fe2O3 + 4H2
- Metals like lead, copper, silver and gold do not react with water or steam.
3. Reaction with dilute acids -
Metals + Dilute acid → Metal salt + Hydrogen
Metals react with dilute HCl to give metal chlorides and hydrogen gas.
i) Sodium
2Na + 2HCl → 2NaCl + H2
ii) Magnesium
Mg + 2HCl → MgCl2 + H2
iii) Aluminium
2Al + 6HCl → 2AlCl3 + 3H2
iv) Zinc
Zn + 2HCl → ZnCl2 + H2
v) Iron
Fe + 2HCl → FeCl2 + H2
vi) Copper, silver and gold do not react with dilute acids. They are less reactive than hydrogen, so they do not displace hydrogen from dilute acids.
Cu + HCl → No reaction
Metals react with dilute sulphuric acid to give metal sulphates and hydrogen gas.
2Na + H2SO4 → Na2SO4 + H2
Mg + H2SO4 → MgSO4 +H2............................
When a metal reacts with dilute nitric acid, then hydrogen gas is not evolved.
( Nitric acid is a strong oxidizing agent , so, as soon as H2 is formed the nitric acid oxidizes it to water.)
Very dilute nitric acid reacts with magnesium and manganese metals to evolve hydrogen gas.
AQUA- REGIA - It is a freshly prepared mixture of 1 part of con. Nitric acid and 3 parts of concentrated HCl. It can dissolve all metals.
REACTIVITY SERIES -
Potassium K (Most reactive metal) Sodium Na Calcium Ca Magnesium Mg Aluminium Al Zinc Zn Iron Fe Tin Sn Lead Pb [Hydrogen] H Copper Cu Mercury Hg Silver Ag Gold Au (Least reactive metal) Reactive metal - When a metal atom can loose electrons easily to form positive ions, it reacts rapidly with other substances .
4. Reaction of metals with Salt Solutions –
A more reactive metal displaces a less reactive metal from its salt solution.
CuSO4 + Zn → ZnSO4 + Cu
( If strip of copper metal is placed in zinc sulphate solution, then no reaction occurs because copper is less rective than zinc)
5. Reaction of Metals with Chlorine –
Metals react with chlorine to form ionic chlorides. Metal elements lose electrons and become positively charged ions, chlorine atoms gain electrons and become negatively charged ions.
IONIC / ELECTROVALENT COMPOUNDS - The compounds formed due to transfer of electrons from a metal to a non-metal. Ionic compounds have strong electrostatic force of attraction between the positive and negative ions. They are electrolytes.
Properties of ionic compounds:
a. Physical nature:- Ionic compounds are solids and are somewhat hard.
b. Melting and Boiling points: - Ionic compounds have high melting and boiling points.
c. Solubility: - Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.
d. Conduction of Electricity: - Ionic compounds do not conduct electricity in the solid state but conduct electricity in the molten state or when dissolved in water.
Na + Cl → NaCl
2, 8, 1 2, 8, 7
2, 8 2, 8, 86. Reaction of Metals with Hydrogen –
Most metals do not combine with hydrogen. Only a few reactive metals like sodium, potassium, calcium and magnesium react with hydrogen to form metal hydrides.
