Metals are very reactive and electropositive elements. Most of the metals combine with water to form metal oxides / metal hydroxides. Some react with cold water, some with hot water and some with steam.
1) Which of the following metals does not react with cold water, but react with hot water to evolve hydrogen gas?
(1) Ca (2) Na (3) Mg (4) AI
(ii) Potassium reacts with cold water to form
(1) K₂O (2) KOH (3) K,Og (4) К(он)
(iii) Which of the following metals does not react with water at all?
(1) Iron (2) Zinc (3) Calcium (4) Lead
(iv) Arrange magnesium, sodium and zinc in the decreasing order of reactivity with water and choose the correct option.
(1) Mg> Na > Zn (2) Na > Mg > Zn (3) Zn > Mg > Na (4) Zn > Na > Mg
Answers
Explanation:
Group 1: Alkali Metals
A common characteristic of most Alkali Metals is their ability to displace H2(g) from water. This is represented by their large, negative electrode potentials. In this event, the Group 1 metal is oxidized to its metal ion and water is reduced to form hydrogen gas and hydroxide ions. The general reaction of an alkali metal (M) with H2O (l) is given in the following equation:
\[\ce{ 2M(s) + 2H2O(l) \longrightarrow 2M^{+}(aq) + 2OH^{-}(aq) + H2 (g)} \]
From this reaction it is apparent that OH- is produced, creating a basic or alkaline environment. Group 1 elements are called alkali metals because of their ability to displace H2(g) from water and create a basic solution.
Alkali metals are also known to react violently and explosively with water. This is because enough heat is given off during the exothermic reaction to ignite the H2(g).
elements also react with water to create basic solutions. Alkali metals react with oxygen to form monoxides, peroxides, or superoxides. These species react with water in different ways:
Monoxides (M2O) produce alkali metal hydroxides:
M2O(s)+2H2O(l)⟶2M+(aq)+2OH−(aq)(2)(2)M2O(s)+2H2O(l)⟶2M+(aq)+2OH−(aq)
Peroxides (M2O2) produce metal hydroxides and hydrogen peroxide:
M2O2(s)+2H2O(l)⟶2M+(aq)+2OH−(aq)+H2O2(aq)(3)(3)M2O2(s)+2H2O(l)⟶2M+(aq)+2OH−(aq)+H2O2(aq)
Superoxides (MO2) produce metal hydroxides, hydrogen peroxide, and oxygen gas:
2MO2(s)+2H2O(l)⟶2M+(aq)+2OH−(aq)+H2O2(aq)+O2(g)(4)
Answer:
io poke Kon shipa haga hagu kor