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 :
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giving $CO _{2}$
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changing into carbonate
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uniting with water
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giving out water
Important constituent of Portland and high alumina cements is?
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$Ca _{3}Al _{2}O _{6}$
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$CaSiO _{3}$
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$CaSO _{4}.2 H _{2}O$
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$Fe _{2}CO _{3}$
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 :
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$CaSO _{4}$
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$CaSO _{4}.H _{2}O$
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$CaSO _{4}.2H _{2}O$
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$CaSO _{4}.Ca(OH) _{2}$
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 $.
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plaster of paris, dead burnt plaster, calcium sulphide
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dead burnt plaster, plaster of paris, lime
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plaster of paris, dead burnt plaster, lime
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anhydrous calcium sulphate, plater of paris, calcium sulphite
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
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Aluminate & Zincate of Calcium
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Zincate and Silicate of Calcium
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Aluminate and Silicate of Calcium
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Aluminate of Calcium and Magnesium
Setting of plaster of Paris involves :
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The oxidation with atmospheric oxygen
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The removal of water to form anhydrous calcium sulfate
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The hydration to form the orthorhombic from of gypsum
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The reaction with atmospheric carbon dioxide gas
The plaster of paris is hardened by
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Liberating ${\text{C}}{{\text{O}} _2}$
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Giving out water
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Combining with water
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Changing into ${\text{CaC}}{{\text{O}} _3}$
Setting of plaster of paris is :
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oxidation with atmospheric oxygen
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combination with atmospheric $CO _2$
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dehydration
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hydration to yield another hydrate
$CaSO _4.1/2H _2O \xrightarrow[setting]{H _2O} CaSO _4.2H _2O \xleftarrow[hardening]{} CaSO _4.2H _2O$
The cementation process is:
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gel formation
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emulsion formation
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both of $A$ and $B$
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none of the above
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.
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Plaster of paris
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Gypsum
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Dead burnt plaster
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Both A and B
Plaster of Paris is stored in air-tight bags because in presence of moisture it changes into gypsum.