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

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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

Cement, the important building material is a mixture of oxides of several elements. Besides calcium, iron and sulphur, oxides of elements of which of the group (s) are present in the mixture?

  1. Group 2

  2. Groups 2, 13 and 14

  3. Groups 2 and 13

  4. Groups 2 and 14
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Cement is a mixture of calcium (present in group 2) and aluminium silicates (contains group 13 and 14 elements).
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

Cement is a mixture of:

  1. calcium silicates

  2. calcium aluminates

  3. calcium silicates and aluminates

  4. none of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Cement is an important building material. It is also called Portland cement. Important ingredients of Portland cement are dicalcium silicate $\left( { Ca } _{ 2 }{ SiO } _{ 4 } \right) 26$%, tricalcium silicate $\left( { Ca } _{ 3 }{ SiO } _{ 5 } \right) 51$% and tricalcium aluminate$\left( { Ca } _{ 3 }{ Al } _{ 2 }{ O } _{ 6 } \right) 11$%.


Hence, cement is a mixture of calcium silicates and aluminates.

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

For the manufacture of cement various steps are given below. Arrange the steps in a proper sequence.


(a) Clinker formation                            (b) Crushing
(c) Addition of gypsum                         (d) Mixing of raw materials
(e) Grinding to fine powder                  (f) Calcination in rotary kiln

  1. d b f a c e

  2. b d f c e a

  3. d c a f e b

  4. a b c d e f
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The order of steps followed in the formation of cement is :
(i) Mixing of raw materials $(d)$
(ii) Crushing $(b)$
(iii) Calcination in a rotary kiln $(f)$
(iv) Clinker formation $(a)$
(v) Addition Gypsum $(c)$
(vi) Grinding to line powder $(e)$


Hence, the correct option is $(A)$.
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

$ Y\xleftarrow[]{\Delta,205^{\circ}C} CaSO 4.2H _2O\  \xrightarrow[]{\Delta,120^{\circ}C} X $. 


$X$ and $Y$ are respectively _____.

  1. plaster of paris, dead burnt plaster

  2. dead burnt plaster, plaster of paris
  3. $CaO$, plaster of paris

  4. plaster of paris, mixture of gases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Reaction of process:


  $CaSO _4 \xleftarrow[]{\Delta,205^{\circ}C} CaSO _4.2H _2O \xrightarrow[]{\Delta,120^{\circ}C} CaSO _4.(1/2)H _2O$                                                                                           (dead burnt plaster)                                          (plaster of paris)
Anhydrous Calcium sulphate is known as dead burnt plaster and $CaSO _4.\cfrac{1}{2} H _2O$ is called plaster of paris.
Hence, the correct option is $A$.

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

In the hardening stage of plaster of paris, the compound formed is :

  1. $CaSO _{4}$
  2. orthorhombic $CaSO _{4} . 2H _{2}O$
  3. $CaSO _{4} . H _{2}O$
  4. monoclinic $CaSO _{4} . 2H _{2}O$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$\underset{\text{plaster of paris}}{CaSO _4.1/2H _2O} \xrightarrow[\text{setting}]{H _2O} \underset{\begin{matrix}\text{gypsum}\\text{orthorhombic}\\text{dihydrate}\end{matrix}}{CaSO _4.2H _2O} \xleftarrow[\text{hardening}]{} \underset{\begin{matrix} \text{gypsum} \\text{monoclinic dihydrate}\end{matrix}}{CaSO _4.2H _2O}$
The plaster of paris absorbs water to form orthorhombic calcium sulfate dihydrate which sets to form a hard mass containing monoclinic $CaSO _4.2H _2O$.

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

Gypsum is added to clinker during cement manufacturing to:

  1. Decrease the rate of setting of cement

  2. Bind the particles of calcium silicate

  3. Facilitate the formation of colloidal gel

  4. All of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

During the cement manufacturing process, upon the cooling of the clinker, a small amount of gypsum is introduced during the final grinding process. Gypsum is added to control the setting of cement. 


If not added, the cement will set immediately after mixing water leaving no time for concrete placing. Hence, the addition of gypsum is required to decrease the rate of setting.


Hence, option $(A)$ is correct.

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 molecular formula of gypsum is :

  1. $CaSO _{4}.H _{2}O$
  2. $CaSO _{4}.2H _{2}O$
  3. $2CaSO _{4}.H _{2}O$
  4. $CaSO _{4}.3H _{2}O$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Gypsum is calcium sulphate dihydrate. Its molecular formula is $ CaSO _{4} \cdot2H _{2}O $. It is an ore of calcium.