Tag: the s-block elements (alkali and alkaline earth metals)

Questions Related to the s-block elements (alkali and alkaline earth metals)

Plaster of paris hardens by :

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. giving $CO _{2}$

  2. changing into carbonate

  3. uniting with water

  4. giving out water

Show answer
Correct Option: C
Explanation:
$\underset{\text{plaster of paris}}{CaSO _4.1/2H _2O} \xrightarrow[\text{setting}]{H _2O} \underset{\begin{matrix}\text{gypsum}\\\text{othorhombic}\\\text{dihydrate}\end{matrix}}{CaSO _4.2H _2O} \xleftarrow[\text{hardening}]{} \underset{\begin{matrix} \text{gypsum} \\\text{monoclinic dihydrate}\end{matrix}}{CaSO _4.2H _2O}$

Plaster of paris absorbs water to form dihydrate, which sets to form a hard unified mass.

Important constituent of Portland and high alumina cements is?

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. $Ca _{3}Al _{2}O _{6}$

  2. $CaSiO _{3}$

  3. $CaSO _{4}.2 H _{2}O$

  4. $Fe _{2}CO _{3}$

Show answer
Correct Option: A
Explanation:

Portland cement essentially consists of compounds of lime(Calcium Oxide CaO) mixed with silica(Silicon dioxide ) and Alumina(Aluminium Oxide).

Plaster of paris in contact with water sets to a hard mass whose composition is :

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. $CaSO _{4}$

  2. $CaSO _{4}.H _{2}O$

  3. $CaSO _{4}.2H _{2}O$

  4. $CaSO _{4}.Ca(OH) _{2}$

Show answer
Correct Option: C
Explanation:

On mixing with water, plaster of paris takes up water of crystallization to form orthorhombic calcium sulphate dihydrate. This sets to a hard mass which is monoclinic calcium sulphate dihydrate or gypsum. This is the final product of setting of plaster of paris. Its composition is $CaSO _4 \cdot 2H _2O $.

$B\xleftarrow[]{200^oC} CaSO _4.2H _2O\xrightarrow[]{120^oC}A$
$\downarrow$ Strongly heated          Gypsum
$C$

A, B and C are respectively :
chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. plaster of paris, dead burnt plaster, calcium sulphide

  2. dead burnt plaster, plaster of paris, lime

  3. plaster of paris, dead burnt plaster, lime

  4. anhydrous calcium sulphate, plater of paris, calcium sulphite

Show answer
Correct Option: C
Explanation:

When calcium sulfate dihydrate is heated to $120^{o} C$, plaster of paris (A) is obtained.
$CaSO _{ 4 }\cdot 2H _{ 2 }O\xrightarrow { 120^o C } CaSO _{ 4 }\cdot \frac { 1 }{ 2 } H _{ 2 }O+\frac { 3 }{ 2 } H _{ 2 }O\ \quad \quad \quad \quad \quad \quad \quad \quad Plaster\quad \quad \quad \quad \quad \ \quad \quad \quad \quad \quad \quad \quad \quad of\ \quad \quad \quad \quad \quad \quad \quad \quad paris\quad  $
When calcium sulfate dihydrate is heated to $200^o C$, anhydrous calcium sulfate is obtained which is known as dead burnt plaster (B).
$CaSO _{ 4 }\cdot 2H _{ 2 }O\xrightarrow { 200^oC } CaSO _{ 4 }+2H _{ 2 }O$
When Dead burnt plaster is strongly heated, lime (C) is obtained.
$CaSO _{ 4 }\xrightarrow { strongly\quad heat } CaO+2SO _{ 3 }$

Cement is mixture of 

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. Aluminate & Zincate of Calcium

  2. Zincate and Silicate of Calcium

  3. Aluminate and Silicate of Calcium

  4. Aluminate of Calcium and Magnesium

Show answer
Correct Option: B

Setting of plaster of Paris involves :

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. The oxidation with atmospheric oxygen

  2. The removal of water to form anhydrous calcium sulfate

  3. The hydration to form the orthorhombic from of gypsum

  4. The reaction with atmospheric carbon dioxide gas

Show answer
Correct Option: A

The plaster of paris is hardened by 

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. Liberating ${\text{C}}{{\text{O}} _2}$

  2. Giving out water

  3. Combining with water

  4. Changing into ${\text{CaC}}{{\text{O}} _3}$

Show answer
Correct Option: C

Setting of plaster of paris is :

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. oxidation with atmospheric oxygen

  2. combination with atmospheric $CO _2$

  3. dehydration

  4. hydration to yield another hydrate

Show answer
Correct Option: D
Explanation:

$CaSO _4.1/2H _2O \xrightarrow[setting]{H _2O} CaSO _4.2H _2O \xleftarrow[hardening]{} CaSO _4.2H _2O$

plaster of paris                       gypsum                                gypsum
                                             orthorhombic                monoclinic dihydrate
                                                 dihydrate

The cementation process is:

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. gel formation

  2. emulsion formation

  3. both of $A$ and $B$

  4. none of the above

Show answer
Correct Option: A
Explanation:

Cementation process is the hardening of cement during the process of construction. The process starts after adding water to the mixture of cement, sand and small stone pieces. In this, a gel type of product is formed which gets thickened and hardened gradually. So cementation is the process of gel formation.

On the basis of following features identify the correct option:
I. It is stored in air-tight bags.
II. It is used in surgical bandages for setting fractured bones.

chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

  1. Plaster of paris

  2. Gypsum

  3. Dead burnt plaster

  4. Both A and B

Show answer
Correct Option: A
Explanation:

Plaster of Paris is stored in air-tight bags because in presence of moisture it changes into gypsum.

plaster of Paris is used in surgical bandages for setting fractured bones because it help in immobilizing of broken bones while they heal.