Tag: chemistry

Questions Related to chemistry

Cement is a 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. calcium silicates

  2. calcium aluminates

  3. calcium silicates and aluminates

  4. none of these

Show answer
Correct Option: C
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.

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

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. 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

Show answer
Correct Option: A
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 $(A)$.

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


$X$ and $Y$ 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

  2. dead burnt plaster, plaster of paris

  3. $CaO$, plaster of paris

  4. plaster of paris, mixture of gases

Show answer
Correct Option: A
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 $A$.

In the hardening stage of plaster of paris, the compound formed 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. orthorhombic $CaSO _{4} . 2H _{2}O$

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

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

Show answer
Correct Option: D
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 $CaSO _4.2H _2O$.

Gypsum is added to clinker during cement manufacturing to:

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. 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

Show answer
Correct Option: A
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.

The molecular formula of gypsum 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. $CaSO _{4}.H _{2}O$

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

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

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

Show answer
Correct Option: B
Explanation:

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

Nitrogen is used to fill electric bulbs because:

chemistry nitrogen and sulfur nitrogen gas component of air - nitrogen nitrogen

  1. it is lighter than air

  2. it makes the bulb to glow

  3. it does not support combustion

  4. it is non-toxic.

Show answer
Correct Option: C
Explanation:

Nitrogen is used because it doesn't react with the hot filament. Then, it will carry heat away form the filament to cool it.

Nitrogen is relatively inactive element because:

chemistry nitrogen and sulfur nitrogen gas component of air - nitrogen nitrogen

  1. its atoms has a stable electronic configuration

  2. it has low atomic radius

  3. its electronegativity is fairly high

  4. dissociation energy of its molecule is fairly high

Show answer
Correct Option: D
Explanation:

Nitrogen is an inactive element as it has a high bond dissociation energy due to the presence of triple bond $N\equiv N$. Hence, viewed as a non-reactive element.

In the fractional evaporation of liquid air, we use :

chemistry nitrogen and sulfur nitrogen gas component of air - nitrogen nitrogen

  1. Dewar flask

  2. Kjeldahl flask

  3. Claude's apparatus

  4. Ramsay apparatus

Show answer
Correct Option: C
Explanation:

We use Claude's apparatus for the fractional evaporation for the fractional evaporation of liquid air.


Option C is correct.

The V A group clement that doesnt directly react with chlorine :

chemistry nitrogen and sulfur nitrogen gas component of air - nitrogen nitrogen

  1. $N _{2}$

  2. As

  3. Sb

  4. Bi

Show answer
Correct Option: A
Explanation:

$N _2$ does not directly react with chlorine because it is noble unreactive gas at room temperature as its bond dissociation energy is high.


Option A is correct.