Tag: some important compounds of magnesium and calcium

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Multiple choice 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

A mixture of slaked lime, sand and water is known as ______.

  1. portland cement

  2. lime mortar

  3. milk of lime

  4. alabaster
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Portland cement contains calcium oxide (quicklime) and clay (silica along with small quantity of alumina, magnesia and ferric oxide).

Multiple choice 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

Plaster of paris hardens by :

  1. giving $CO _{2}$

  2. changing into carbonate

  3. uniting with water

  4. giving out water
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice 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

Important constituent of Portland and high alumina cements is?

  1. $Ca _{3}Al _{2}O _{6}$
  2. $CaSiO _{3}$
  3. $CaSO _{4}.2 H _{2}O$
  4. $Fe _{2}CO _{3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice 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

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

  1. $CaSO _{4}$
  2. $CaSO _{4}.H _{2}O$
  3. $CaSO _{4}.2H _{2}O$
  4. $CaSO _{4}.Ca(OH) _{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $.

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

A, B and C are respectively :

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
$CaSO _{ 4 }\xrightarrow { strongly\quad heat } CaO+2SO _{ 3 }$

Multiple choice 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

The plaster of paris is hardened by 

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

  2. Giving out water

  3. Combining with water
  4. Changing into ${\text{CaC}}{{\text{O}} _3}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Plaster of Paris hardens by reacting with water to form a solid mass of gypsum crystals, a process known as hydration.

Multiple choice 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

Setting of plaster of paris is :

  1. oxidation with atmospheric oxygen
  2. combination with atmospheric $CO _2$

  3. dehydration

  4. hydration to yield another hydrate
Reveal answer Fill a bubble to check yourself
D Correct answer
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

Multiple choice 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

The cementation process is:

  1. gel formation

  2. emulsion formation
  3. both of $A$ and $B$

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
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.