Oxides and Hydroxides Class 11 Notes | EduRev

Chemistry Class 11

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Class 11 : Oxides and Hydroxides Class 11 Notes | EduRev

The document Oxides and Hydroxides Class 11 Notes | EduRev is a part of the Class 11 Course Chemistry Class 11.
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Oxides and Hydroxides

Group - I & II

OXIDES

Sodium Oxide (Na2O) :

Preparation :

(i) It is obtained by burning sodium at 180°C in a limited supply of air or oxygen and distilling off the excess of sodium in vacuum.

Oxides and Hydroxides Class 11 Notes | EduRev

(ii) By heating sodium peroxide, nitrate or nitrite with sodium.

Oxides and Hydroxides Class 11 Notes | EduRev

Properties:

(i)  It is white amorphous mass.

(ii)  It decomposes at 400°C into sodium peroxide and sodium.

Oxides and Hydroxides Class 11 Notes | EduRev

(iii) It dissolves violently in water, yielding caustic soda.

Na2O + H2O -----> 2NaOH

Sodium Peroxides (Na2O2) :

Preparation: It is formed by heating the metal in excess of air or oxygen at 300°, which is free from moisture and CO2.

2Na + O2 -----> Na2O2

Properties :

(i) It is a pale yellow solid, becoming white in air from the formation of a film of NaOH and Na2CO3.

(ii)  In cold water (~ 0°C) produces H2O2 but at room temperature produces O2. In ice-cold mineral acids also produces H2O2.

Oxides and Hydroxides Class 11 Notes | EduRev

(iii) It reacts with CO2, giving sodium carbonate and oxygen and hence it is used for purifying air in a confined space e.g. submarine, ill-ventilated room.

2Na2O2 + 2CO2 -----> 2Na2CO3 + O2

(iv)  It is an oxidising agent and oxidises charcoal, CO, NH3, SO2.

3Na2O2 + 2C -----> 2Na2CO3 + 2Na [Deposition of metallic Na]

CO + Na2O2 ------> Na2CO

SO2 + Na2O2 ------> Na2SO

2NH3 + 3Na2O2 ------> 6NaOH + N2

(v) It contains peroxide ion [-O-O-]-2. 

Uses 

(i) For preparing H2O2, O2.
(ii) Oxygenating the air in submarines.
(iii) Oxidising agent in the laboratory.


Oxides of Potassium:

 

K2O,

K2O2

K2O3

KO2         

KO3

Colours:

White

White

Red

Bright Yellow

Orange Solid

 

Oxides and Hydroxides Class 11 Notes | EduRev

Oxides and Hydroxides Class 11 Notes | EduRev

 

(iii) Passage of O2 through a blue solution of K in liquid NH3 yields oxides K2O2 (white), K2O3 (red) and KO(deep yellow) i.e;

Oxides and Hydroxides Class 11 Notes | EduRev

Oxides and Hydroxides Class 11 Notes | EduRev

Magesium Oxide (MgO):

It is also called magnesia and obtained by heating natural magnesite.

MgCO3--------- >. MgO + CO2

Properties:

(i)  It is white powder.

(ii)  It's m.p. is 2850°C. Hence used in manufacture of refractory bricks for furances.

(iii) It is very slightly soluble in water imparting alkaline reaction.

Calcium Oxide (CaO) :

It is commonly called as quick lime or lime and made by decomposing lime stone at high temperature about 1000°C.

CaCO3 ---------> CaO + CO2 + 42,000 cal

Properties:

1. It is white amorphous powder of m.p. 2570°C.

2. It emits intense light (lime light), when heated in oxygen - hydrogen flame.

3. It is a basic oxide and combines with some acidic oxide e.g.

CaO + SiO---- >. CaSiO3

CaO + CO2 ------> CaCO3

4. It combines with water to produce slaked lime.

CaO + H2O------ >. Ca(OH)2

Magnesium Peroxide (MgO2) and Calcium Peroxide (CaO2) :

These are obtained by passing H2O2 in a suspension of Mg(OH)2 and Ca(OH)2.

Uses: MgO2 is used as an antiseptic in toothpaste and as a bleaching agent.

 

Hydroxides

Sodium Hydroxides:

 Preparation:

(i) Electrolysis of Brine:

Oxides and Hydroxides Class 11 Notes | EduRev

(ii) Caustication of Na2CO3 (Gossage's method):

Oxides and Hydroxides Class 11 Notes | EduRev

Since the Ksp(CaCO3) < Ksp(Ca(OH)2), the reaction shifts towards right.

Properties.

(i) It is white crystalline, deliquescent, highly corrosive solid.

(ii) It is stable towards heat.

(iii)  It's aqueous solution alkaline in nature and soapy in touch.

(iv)  Oxides and Hydroxides Class 11 Notes | EduRev
Oxides and Hydroxides Class 11 Notes | EduRev

(v) Acidic and amphoteric oxides gets dissolved easily e.g.

CO2 + 2NaOH   ---> Na2CO3 + H2O

Al2O3 + 2NaOH- ---> 2NaAlO2 + H2O

(vi) Aluminium and Zn metal gives H2 from NaOH.

2Al + 2NaOH + 2H2O --->3H2 + 2NaAlO2

(vii) Several non metals such as P, S, Cl etc. yield a hydride instead of hydrogen e.g.

4P + 3NaOH + 3H2O --->PH3 + 3NaH2PO2 (Disproportionation reaction)

 

Potassium Hydroxide :
Preparation : Electrolysis of KCl aqueous solution
Properties : Same as NaOH
**(a) It is stronger base compared to NaOH.
(b) Solubility in water is more compared to NaOH.
(c) In alcohol, NaOH is sparingly soluble but KOH is highly soluble.
(d) As a reagent KOH is less frequently used but in absorption of CO2, KOH is preferably used compared to NaOH. Because KHCO3 formed is soluble whereas NaHCO3 is insoluble and may therefore choke the tubes of apparatus used.

Magnesium Hydroxide : It occurs in nature as the mineral brucite.

Preparation : It can be prepared by adding caustic soda solution to a solution.

 Mg+2 + 2NaOH ------>Na2SO4 + Mg(OH)2

Properties:

1. It can be dried at temperature upto 100°C only otherwise it breaks into its oxide at higher temperature.

Mg(OH)2------> MgO + H2O

2. It is slightly soluble in water imparting alkalinity.

3. It dissolves in NH4Cl solution.

Mg(OH)2 + 2NH4Cl ------> MgCl2 + 2NH4OH

**Thus, Mg(OH)2 is not, therefore, precipitated from a solution of Mg+2 ions by NH4OH in presence of excess of NH4Cl.

Calcium Hydroxide:

Preparation : By spraying water on quicklime.
CaO + H2O ----> Ca(OH)2

Properties:
(i) It is sparingly soluble in water.
(ii) It's solubility in hot water is less than that of cold water. Hence solubility decreases with increase in temperature.
(iii) It readily absorbs CO2  and used as a test for the gas.
(iv) It is used as a mortar.
[Mortar is a mixture of slaked lime (1 part) and sand (3 parts) made into a paste with water].

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