Tag: some important compounds of calcium

Questions Related to some important compounds of calcium

Portland cement consists essentially of compounds 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. lime (calcium oxide, $CaO$)

  2. silica (silicon dioxide, $SiO _2$)

  3. alumina (aluminum oxide, $Al _2O _3$)

  4. all of them

Show answer
Correct Option: D
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.

Metal oxide that turns into cement upon roasting with clay 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. $NO$

  2. $MgO$

  3. $BaO$

  4. $CaO$

Show answer
Correct Option: D
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 $CaO$.

Final setting time of cement should not be more than:

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. 1 hour

  2. 2 hours

  3. 5 hours

  4. 10 hours

Show answer
Correct Option: D
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.

Which of the following is not present in portland cement?

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. $Ca _3Al _2O _6$

  2. $Ca _3SiO _5$

  3. $Ca _2SiO _4$

  4. $Ca _3(PO _4) _2$

Show answer
Correct Option: D
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.

When plaster of paris comes in contact with water it sets into a hard mass. The composition of the hard mass 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. $CaSO _4.H _2O$

  2. $CaSO _4.Ca(OH) _2$

  3. $CaSO _4.2H _2O$

  4. $CaSO _4.2Ca(OH) _2$

Show answer
Correct Option: C
Explanation:

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

Plaster of paris is obtained by heating gypsum at 373 K.

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. True

  2. False

Show answer
Correct Option: B
Explanation:

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

Plaster of Paris has the formula:

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

  2. $CaSO _4.H _2O$

  3. $CaSO _4.2H _2O$

  4. none of the above

Show answer
Correct Option: A
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).

Gypsum is added to Portland cement 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. 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

Show answer
Correct Option: B
Explanation:

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

The average composition of Portland cement 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. $CaO : 40 - 50\%$, $SiO _2 : 30 - 40\%$, $Al _2O _3$ 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. $CaO : 50\%$, $SiO _2 : 50\%$

Show answer
Correct Option: B
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.

Cement is formed by burning of _________ in a hot 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. limestone and clay

  2. limestone and graphite

  3. chalk and graphite

  4. sulphur and limestone

Show answer
Correct Option: B
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.