Railway Science (Chemistry-Metals , Non-Metals and Alloys) (Part-III)

Alloy is a mixture of two or more metals, or a metal and a nonmetal. A colloid is a mixture in which one substance of dispersed insoluble particles is suspended throughout another substance. Emulsion is a colloidal solution where both dispersed phase and dispersed medium are liquids.
Examples - Milk, face cream etc. Heterogeneous mixture - A mixture in which the components are not uniformly distributed through its volume. Example - Mixture of salt and iron powder.

All metals are not reactive equally. A highly reactive metal displaces less reactive metals from its salt solution. Example - If Zinc is placed in copper sulphate solution then zinc will displace the copper from the solution.
Zn(Zinc) + CuSO₄ (Copper Sulphate) → ZnSO₄ (Zinc Sulphate) + Cu (Copper). Some of the common metals are arranged in reactivity series - K (Potassium) > Na (Sodium) > Ca (Calcium) > Mg (Magnesium) > Al (Aluminium) > Zn (Zinc) > Fe (Iron) > Pb (Lead) > H (Hydrogen) > Cu (Copper) > Hg (Mercury) > Ag (Silver) > Au (Gold) > Pt (Platinum).

Metals - Elements which form positive ions by losing electrons in chemical reactions except hydrogen. Example - Gold (Au), Silver (Ag) and Nickel (Ni). Non-metals - Elements that tend to gain electrons to form anions during chemical reactions.
Example - H₂(g), N₂(g), O₂(g), and Cl₂(g). Metalloids: Those elements which have properties of both metals and nonmetals . Examples - Silicon (Si), Germanium (Ge), Arsenic (As), Boron (B), Tellurium (Te) and Polonium (Po).

Metals: Shiny in appearance, good conductors of electricity, strong and hard, malleable and ductile. Malleability - The property of a substance that describes its ability to bend or is hammered into a thin sheet without breaking. Gold (Au) is the most malleable and ductile metals. Nickel (Ni) is the least malleable. Exception: Sodium (Na) and Potassium (K) are soft and can be easily cut by a knife.

It is a natural process that converts a refined metal into a more chemically stable oxide. Acidity - Medical condition that is caused due to excess production of acid by the glands of the stomach. Reduction - Any of a class of chemical reactions in which the number of electrons associated with an atom or a group of atoms is increased.

Also, Iron (Fe) and Zinc (Zn) do not react with cold or hot water. Metals which react with water are Lithium (Li) , Sodium (Na), Potassium (K) , Rubidium (Rb) , Caesium (Cs), and Francium (Fr). Metal oxide and hydrogen gas is created when a metal and water reacts together. Oxides are produced when zinc, aluminium and steam react.

(Symbol - Na, Atomic number - 11, Group - 1): It is high in the reactivity series and metals high in the reactivity series have more affinity for oxygen than carbon, Other metals high up in the reactivity are Magnesium (Mg, Atomic number 12), Calcium (Ca, 20), Aluminium (Al, 13).
Carbon (C, 6) cannot reduce all metals; The ability of carbon to reduce a metal is based upon its relative reactivity as compared to the metal; Carbon can only reduce those metal oxides whose metals have less reactivity than carbon. Copper (Cu, 29, group 11). Zinc (Zn, 30, Group 12). Iron (Fe, 26, group 8).

K + H₂O → KOH + H₂ ; Hydrogen gas is emitted and the metal hydroxide is produced. Sodium too reacts violently with cold water. The reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.

Silver (Ag, Atomic number 47). Properties - White, lustrous, soft, very ductile, malleable, excellent conductor of heat and electricity, quite an unreactive metal.
Uses - Dental alloys, solder and brazing alloys, electrical contacts and batteries, Silver paints (making printed circuits). Potassium (K) - Most Reactive, Atomic Number 19; Platinum (Pt) - Least Reactive, Atomic Number 78.

Non-metals have more than 4 valence electrons located right side of the periodic table. Example: Nitrogen (N₂), Oxygen (O₂) and Fluorine (F₂) contain 5, 6 or 7 numbers of electrons respectively in their outermost shell. Metals are electropositive elements, have 1, 2 or 3 electrons in the outermost shell (or valence shell) of their atoms.