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

Portland cement consists essentially of compounds of:

  1. lime (calcium oxide, $CaO$)
  2. silica (silicon dioxide, $SiO _2$)
  3. alumina (aluminum oxide, $Al _2O _3$)

  4. all of them
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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.

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

Metal oxide that turns into cement upon roasting with clay is:

  1. $NO$
  2. $MgO$
  3. $BaO$
  4. $CaO$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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 $CaO$.

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

Final setting time of cement should not be more than:

  1. 1 hour

  2. 2 hours

  3. 5 hours

  4. 10 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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.

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 not present in portland cement?

  1. $Ca _3Al _2O _6$
  2. $Ca _3SiO _5$
  3. $Ca _2SiO _4$
  4. $Ca _3(PO _4) _2$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • 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.
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

When plaster of paris comes in contact with water it sets into a hard mass. The composition of the hard mass is:

  1. $CaSO _4.H _2O$
  2. $CaSO _4.Ca(OH) _2$
  3. $CaSO _4.2H _2O$
  4. $CaSO _4.2Ca(OH) _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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 is obtained by heating gypsum at 373 K.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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 has the formula:

  1. $CaSO _4.(1/2)H _2O$
  2. $CaSO _4.H _2O$
  3. $CaSO _4.2H _2O$

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

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

Hence the correct answer is option (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

Gypsum is added to Portland cement to:

  1. fasten the process of setting

  2. slow down the process of setting

  3. improve the colour of the cement

  4. increase the melting point of cement
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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 average composition of Portland cement is:

  1. $CaO : 40 - 50\%$, $SiO _2 : 30 - 40\%$, $Al _2O _3$ and $Fe _2O _3 : 10 - 20\%$
  2. $CaO : 50 - 60\%$, $SiO _2 : 20 - 25\%$, $Al _2O _3 : 5 - 10\%$, $MgO : 2 - 3\%, Fe _2O _3 : 1 - 2\%$ and $SO _3 : 1 - 2\%$
  3. $SiO _2 : 40 - 50\%$, $CaO : 30 - 40\%$, $Al _2O _3 : 10 - 20\%$
  4. $CaO : 50\%$, $SiO _2 : 50\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

$ CaO \rightarrow 50-60$%
$ SiO _2 \rightarrow 20-25$%
$ Al _2O _3 \rightarrow 5-10$%
$ Fe _2O _3 \rightarrow 1-2$%
$ MgO \rightarrow 2-3$%
$ SO _3 \rightarrow 1-2$%
and few amount of oxides of iron, magnesium and sulphur.

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 formed by burning of _________ in a hot kiln.

  1. limestone and clay

  2. limestone and graphite

  3. chalk and graphite

  4. sulphur and limestone
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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.