What is meant by the activity series of metals? Compare the activity of sodium and iron with air, water and dilute acids.

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Solution

Activity series: Metals are arranged in a vertical column in the decreasing order of their reactivity. This vertical column is called the activity series of metals. The most reactive metals are placed on the top, while the least reactive metals are placed at the bottom of the activity series.

Activity Series of Metals:

K (Most reactive)
Na
Ca
Mg
Al
Zn
Fe
Sn
Pb
H
Cu
Hg
Ag
Au (Least reactive)

Reactivity towards Sodium Iron

Air It is one of the most reactive metal so it forms oxide when exposed to air.
4Na + O₂ →2Na₂O
It is a moderately reactive metal and it rusts in moist air and burns when heated strongly in air.
4Fe + 3O₂ → 2Fe₂O₃

Water It reacts vigorously with cold water to form sodium hydroxide and liberates hydrogen gas.
2Na + 2H₂O → 2NaOH + H₂ It does not react with cold water or steam, but red hot iron reacts reversibly with steam to form tri-iron tetroxide and hydrogen gas.
3 Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂

Dilute acids It reacts violently with dilute acids and liberates hydrogen gas.
2Na + 2HCl→ 2NaCl + H₂ It reacts slowly with dilute acids and liberates hydrogen.
Fe + H₂SO₄→ FeSO₄ + H₂

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Similar questions

Choose terms from the options given in brackets to complete these sentences.

(a) When CuO reacts with hydrogen, .............. is reduced and ............... is oxidized to .............. . $(C u O, H_{2}, C u, H_{2} O)$

(b) Hydrogen is ................ soluble in water. (Sparingly, highly, moderately)

(iron, magnesium, aluminium, sodium, calcium)

(d) Sodium .......... reacts smootly with cold water. (metal, amalgam, in the molten state)

(e) A metal ............. hydrogen in the activity series gives hydrogen with ............... acid or acid.

(above, below, dilute hydrochloric, concentrated hydrochloric, dilute sulphuric).

Give reason for the following :

(a) Though lead is above hydrogen in the activity series, it does not react with dilute hydrochloric acid or dilute sulphuric acid.

(b) Potassium and sodium are not used fro reaction with dilute hydrochloric acid or dilute sulphuric acid in laboratory preparation of hydrogen.

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Reactivity towards	Sodium	Iron
Air	It is one of the most reactive metal so it forms oxide when exposed to air. 4Na + O₂ →2Na₂O	It is a moderately reactive metal and it rusts in moist air and burns when heated strongly in air. 4Fe + 3O₂ → 2Fe₂O₃
Water	It reacts vigorously with cold water to form sodium hydroxide and liberates hydrogen gas. 2Na + 2H₂O → 2NaOH + H₂	It does not react with cold water or steam, but red hot iron reacts reversibly with steam to form tri-iron tetroxide and hydrogen gas. 3 Fe + 4H₂O ⇌ Fe₃O₄ + 4H₂
Dilute acids	It reacts violently with dilute acids and liberates hydrogen gas. 2Na + 2HCl→ 2NaCl + H₂	It reacts slowly with dilute acids and liberates hydrogen. Fe + H₂SO₄→ FeSO₄ + H₂