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

Which of the following is/are the raw materials used to manufacture cement?

  1. Clay

  2. Limestone

  3. Calcium sulphate

  4. Slaked lime
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

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

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

Which of the following is used to regulate setting rate?

  1. Slaked lime

  2. Limestone

  3. Plaster of Paris

  4. Gypsum
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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.

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 cement in order to:

  1. prolong hydration

  2. increase strength after hydration

  3. decrease heat of hydration

  4. reduce curing time
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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.

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 process of formation of colloidal gel from calcium silicate and aluminates is:

  1. endothermic

  2. exothermic

  3. reversible
  4. both $B$ and $C$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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.

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

Which of the following cement is used in the high-temperature application?

  1. Expansive cement

  2. High-Alumina cement

  3. Portland blast-furnace slag cement

  4. Portland pozzolan cement
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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.

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

What does RCC stands for?

  1. Reinforced Cement Concrete

  2. Regenerative Concrete Cement

  3. Reinforced Carbon Cement

  4. Reinforced Core Concrete
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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.

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

Which of the following is/ are correct statement(s)?

  1. Portland cement is the most commonly used cement for construction work.

  2. 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).

  3. Portland cement gets its name from the stone quarried from the Isle of Portland in England which has a similar texture.

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

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.

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

Which of the following is/ are correct statement(s)?

  1. Cement is an important material in electronic industry.

  2. Sheets, blocks, pillars and pipes are made from concrete produced from cement.

  3. Cement is a wet white powder with coarse particles.

  4. Cement is made from silica (sand), alumina, lime, iron oxide and magnesia.
Reveal answer Fill a bubble to check yourself
B,D Correct answer
Explanation

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.

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

Portland cement is not used in:

  1. manufacture of bricks

  2. manufacture of pipes, beams

  3. manufacture of railroad ties

  4. manufacture of rails
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Portland cement is used in the manufacture of

-bricks
-pipes, beams
-railroad ties
But Portland cement is not used in the manufacture of rails. These rails are built of an alloy.