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Physical Properties of Metals

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notes

WHEN METALS REACT WITH ACIDS:-

Metals react with acids to give salt and hydrogen gas.

Metal + Dilute acid → Salt + Hydrogen

2Na(s) + 2HCl(aq) → 2NaCl(aq) + H2(g)

Hydrogen gas is not evolved when a metal reacts with nitric acid. It is because HNO3 is a strong oxidising agent. It oxidises the H2 produced to water and itself gets reduced to any of the nitrogen oxides (N2O, NO, NO2).

The reactivity or activity series is a list of metals arranged in the order of their decreasing activities. The reactivity decreases in the order

Mg > Al > Zn > Fe



notes

METALS REACTION WITH WATER:-

Metal react with water and produce a metal oxide and hydrogen gas. But all the metals do not react with water.

Metal + Water Metal oxide + Hydrogen

Metal Oxide + Water Metal hydroxide

Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.

2K(s) + 2H2O(l) 2KOH(aq) + H2(g) + heat energy

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) + heat energy

The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire.

Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)

Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal.

Magnesium does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen. It also starts floating due to the bubbles of hydrogen gas sticking to its surface.

Metals like aluminium, iron and zinc react with steam to form the metal oxide and hydrogen

2Al(s) + 3H2O(g) → Al2O3(s) + 3H2(g)

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

Metals such as lead, copper, silver and gold do not react with water at all.

notes

The Reactivity Series:-

K > Na > Ca > Mg > Al > Zn > Fe >Pb >H > Cu > Hg > Ag > Au

notes

METALS REACTION WITH AIR:-

Metals react with air to form metal oxides

Metal + Oxygen Metal Oxide

example:-

4Fe + 3O22Fe2O3

Iron reacts with oxygen to form iron oxide commonly known as Rust

2Cu + O2 → 2CuO

when copper is heated in air, it combines with oxygen to form copper(II) oxide, a black oxide.

Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.

Silver and gold do not react with oxygen even at high temperatures.

notes

WHEN METALS REACT WITH SOLUTION OF OTHER METAL SALTS:-

Reactive metals can displace less reactive metals from their compounds in solution or molten form.

Metal A + Salt solution of B → Salt solution of A + Metal B

The Reactivity Series:-

K > Na > Ca > Mg > Al > Zn > Fe >Pb >H > Cu > Hg > Ag > Au

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Shaalaa.com | Metal and Non Metals part 6 (Anodising)

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