Some important compounds of calcium - class-XI

The reaction of water with calcium oxide (quicklime) to form slaked lime is highly exothermic. To study it safely, one typically adds small amounts of water to the lime or vice-versa under controlled conditions, but the standard laboratory demonstration involves adding water to the solid.

$ACa(HCO _3) _2 + BCa(OH) _2 \rightarrow CCaCO _3 + DH _2O$

$CaO$ is a compound that absorbs moisture easily and rapidly.

Correct order of thermal stability of carbonates of alkaline earth metals is
$BeCO _3 < MgCO _3 < CaCO _3 < SrCO _3 < BaCO _3$

On hydration of Plaster of Paris, converts into Gypsum.
$\underset {\text {Plaster of Paris}}{CaSO _{4} \cdot \dfrac {1}{2} H _{2}O} + \dfrac {3}{2} H _{2}O\rightarrow \underset {Gypsum}{CaSO _{4}\cdot 2H _{2}O}$

Some of the uses ofplaster of paris are as follows :-

Absorption of $CO _{2}$ from atmospheric air contributes for strengthening for lime mortar structure as when atmospheric $CO _{2}$ combines with hydrated lime, limestone is formed which is a solid.

Two of the raw materials for the manufacture of cement are limestone and clay.

Limestone and clay are raw materials used in the manufacture of portland cement.

Magnesium salt is also known as epsom salt. Chemical formula of epsom salt is $MgSO _4.7H _2O$.

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

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

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 $.

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.
$CaSO _{ 4 }\xrightarrow { strongly\quad heat } CaO+2SO _{ 3 }$

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

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

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.

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

Plaster of paris is calcium sulphate and addition of water of crystallization to it leads to formation of gypsum which becomes hard material. It should be stored in water proof container.
${ CaSO } _{ 4 }\cdot \dfrac { 1 }{ 2 } { H } _{ 2 }O+\dfrac { 3 }{ 2 } { H } _{ 2 }O\rightarrow { CaSO } _{ 4 }\cdot 2{ H } _{ 2 }O$

When water is mixed with cement to form a paste, reaction starts. In its pure form, the finely ground cement is extremely sensitive to water. Out of the three main compounds, $C _3A, C _3S \ and \ C _2S$, reacts quickly with water to produce a jelly-like compound which starts solidifying.

When magnesium oxide reacts with magnesium chloride it forms Sorrel cement.

Portland cement is the most common type of cement general use around the world, used as a basic ingredient of concrete mortar, stucco and most non-speciality grout. It developed from other types of hydraulic lime in England in the mid 19th century and usually originates from limestone. 

Hydraulic cement are made up of a mixture of silicates and oxides in the form of silicon dioxide. It is responsible for the mechanical properties of cement.

It consists of calcium silicates and the ratio of calcium oxide to silicon dioxide is not less than 2. It consists of MgO not more than 5% by mass.

Plaster of Paris is prepared by gypsum. 

Portland cement consists
essentially of compounds of lime (calcium oxide, $CaO$) mixed with silica
(silicon dioxide, $SiO _2$) and alumina (aluminum oxide, $Al _2O _3$). 

The raw materials needed to produce cement (calcium carbonate, silica, alumina and iron ore) are generally extracted from limestone rock, chalk, clayey schist or clay.

Concrete is a building material that has high compressive strength and low tensile strength and is composed of a mixture of cement, gravel and sand (aggregates), and water.

Plaster of Paris is made by heating the mineral gypsum. When gypsum is heated to about 150°C it losses water and produces the powder of plaster of Paris.

This glass is typically made using a wet batch process where the composition is primarily limestone, soda ash and silica. 

Plaster of Paris is prepared by heating gypsum to $120-180℃$.

Cement is manufactured through a controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients. which is used in construction of building.

The given statement is true. Limestone, sand, gypsum and coal dust are the materials required for the manufacture of cement.

For nominal mix design, the standard ratio between cement, gravel and sand, which is as follows:

|
Grade
|
Cement          :
|
Gravel            :
|
Sand

|
| --- | --- | --- | --- |
|
M5
|
1
|
5
|
10
|
|
M7.5
|
1
|
4
|
8
|
|
M10
|
1
|
3
|
6
|
|
M15
|
1
|
2
|
4
|
|
M20
|
1
|
1
|
3
|
|
M25
|
1
|
1
|
2
|

In the manufacture of Portland cement, clinker occurs as lumps or nodules, usually 3 millimetres (0.12 in) to 25 millimetres (0.98 in) in diameter, produced by sintering (fused together without melting to the point of liquefaction) limestone and alumino-silicate materials such as clay during the cement kiln stage.

A rotary kiln is a pyroprocessing device used to raise materials to a high temperature (calcination) in a continuous process. Materials produced using rotary kilns include cement, lime.

Cement kilns are used for the pyro-processing stage of manufacture of Portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates.

A cement is a binder, a substance used in construction that sets and hardens and can bind other materials together. The most important types of cement are used as a component in the production of mortar in masonry, and of concrete, which is a combination of cement and an aggregate to form a strong building material.

The most common raw rock types used in cement production are:

1. Limestone (supplies the bulk of the lime)
2. Clay, marl or shale (supplies the bulk of the silica, alumina and ferric oxide)
3. Other supplementary materials such as sand, fly ash/pulverised fuel ash (PFA), or ironstone to achieve the desired bulk composition

Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat. The major reason is that C3A in the clinker can dissolve in water quickly to generate a kind of calcium aluminate hydrate, a clotting agent, which will destroy the normal use of cement. The retardation mechanism of gypsum is: when cement is hydrated, gypsum reacts with C3A quickly to generate calcium sulfoaluminate hydrate which deposits and forms a protection film on the cement particles to hinder the hydration of C3A and delay the setting time of cement.

Gypsum is called the retarding agent of cement which is mainly used for regulating the setting time of cement and is an indispensable component. Without gypsum, cement clinker can condense immediately by mixing with water and release heat. The major reason is that C3A in the clinker can dissolve in water quickly to generate a kind of calcium aluminate hydrate, a clotting agent, which will destroy the normal use of cement. The retardation mechanism of gypsum is: when cement is hydrated, gypsum reacts with C3A quickly to generate calcium sulfoaluminate hydrate which deposits and forms a protection film on the cement particles to hinder the hydration of C3A and delay the setting time of cement.

The first stage of hydration is characterized by the rapid dissolution of clinker

${ Ca } _{ 3 }Si{ O } _{ 5 }+3{ H } _{ 2 }O\longrightarrow 3{ Ca }^{ 2+ }+4{ OH }^{ - }+{ H } _{ 2 }Si{ O } _{ 2 }^{ 4- }$

 immediately after the wetting of the clinker powder. In calorimetry measurements,  a large exothermic signal is measured due to wetting and dissolution of clinker. The wet clinker releases ions such as calcium, silicate and hydroxide to the solution. From the evolution of these ion concentrations the dissolution rate of clinker can be evaluated.

Because of their relatively high cost, calcium aluminate cements are used in a number of restricted applications where performance achieved justifies costs:

1. In construction concretes, where rapid strength development is required, even at low temperatures.
2. As a protective liner against microbial corrosion such as in sewer infrastructure.
3. In refractory concretes, where strength is required at high temperatures.
4. As a component in blended cement formulations, for various properties such as ultra-rapid strength development and controlled expansion are required.
5. In sewer networks for their high resistance to biogenic sulfide corrosion.

Its full name is reinforced cement concrete, or RCC. RCC is concrete that contains steel bars, called reinforcement bars, or rebars. This combination works very well, as concrete is very strong in compression, easy to produce at site, and inexpensive, and steel is very very strong in tension.

all given options are correct . Sheets, blocks, pillar and pipes are made from concrete produced from cement.

All of the following statements are correct.
Portland cement is the most commonly used cement for construction work.
Portland cement is made from raw material which consist of 60% lime (calcium oxide), 25% silica (silicon dioxide), 5% alumina. The rest is iron oxide and gypsum (calcium sulphate).
Portland cement gets its name from the stone  quarried from the Isle of Portland in England which has a similar texture.

The options (B) and (D) are correct statements.
Cement is an important material in construction.
Sheets, blocks, pillars and pipes are made from concrete produced from cement.
Cement is a dry greenish grey powder with fine particles.
Cement is made from silica (sand), alumina, lime, iron oxide and magnesia.

Portland cement is used in the manufacture of

Limestone, sand, gypsum and coal dust are the materials required for the manufacture of cement. Lime, silica and alumina are contained in the above materials. Hence, the right answer is all of them.

Quicklime when roasted with clay forms cement. Calcium oxide is also called as quicklime. Hence, the metal oxide that forms clay on roasting with clay is $CaO$.

Initial setting time of cement should be more than 45 mins. This is to allow enough time for transportation and placing of concrete before setting starts. Final setting time should be less than 375 minutes. 375 minutes is equivalent to 10.25 hours. Hence, the final setting time of cement should not be more than 10 hours.

• Portland cement gets its strength from chemical reactions between the cement and water. The process is known as hydration.
  
• Chemical composition of portland cements are-

1.  $Ca _3Al _2O _6$
   
2. $Ca _3SiO _5$
   
3. $Ca _2SiO _4$
   
4. $Na _2O$
5. $K _2O$
6. $CaSO _4.2H _2O$
   
7. $Ca _4Al _2Fe _2O _{10}$
   

• Hence option D is not present in portland cement.

When plaster of paris comes in contact with water it sets into a hard mass which is called gypsum. Its composition is $CaSO _4.2H _2O$

Plaster of Paris is obtained by heating gypsum or calcium sulphate dihydrate at 373 K in a kiln.
$\displaystyle CaSO _4 \cdot 2H _2O \xrightarrow {373 K} CaSO _4 \cdot \dfrac {1}{2} H _2O$

The composition of plaster of paris is $CaSO _4.(1/2)H _2O$ and the composition of gypsum is $CaSO _4.2H _2O$.

Gypsum slows down the process of setting of the cement so that it gets sufficiently hardened.

Port land cement consists of raw materials mainly compounds of lime mixed with silica and alumina.

Cement is formed by burning of graphite and limestone in a hot kiln. Many other materials such as shells , chalk or marl combined with shale, clay, slate blast furnace slag , silica sand and iron ore are also used in manufacture of cement.

The mold made from plaster of paris can be conserved for a long time and thus crime detectives make use of it so that they get exact impression and can preserve it for future use.

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$\left( { Ca } _{ 3 }{ Al } _{ 2 }{ O } _{ 6 } \right) 11$%.

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. 

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