Tag: some important compounds of magnesium and calcium

Questions Related to some important compounds of magnesium and calcium

Magnesium may be called a refractory because it?

some important compounds of magnesium and calcium the s-block elements chemistry

  1. has high melting point

  2. is a good conductor of heat

  3. is chemically inert as well as an electrical insulator

  4. forms Grignard's reagent

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Correct Option: A
Explanation:
  • A refractory material or refractory is a heat-resistant material
  • Magnesium oxide is used to make linings for some furnaces. It is known as a refractory material - which just means that it is resistant to heat. You may have come across this on the CIE page about ceramics. Magnesium oxide has a high melting point (2852°C) and so resists the high temperatures in a furnace.

Which of the following is useful in diagnosing stomach in X-ray picture?

some important compounds of magnesium and calcium the s-block elements chemistry

  1. $Mg(OH) _2$

  2. $BaSO _4$

  3. $Na _2CO _3$

  4. $Ba(OH) _2$

Show answer
Correct Option: B
Explanation:

A suspension of Barium sulphate $(BaSO _4)$, a chalky powder, is ingested in to patient at the time of X-ray. Barium coated areas of the digestive tract then appear on an X-ray as white.

Gypsum, $CaSO _4.2H _2O$, on heating to about $120^0C$ forms a compound which has the chemical composition represented by 

some important compounds of magnesium and calcium the s-block elements chemistry

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

  2. $CaSO _4$

  3. $CaSO _4.H _2O$

  4. $2CaSO _4.3H _2O$

Show answer
Correct Option: A

In aqueous solution, the most stable sulphate is :

some important compounds of magnesium and calcium the s-block elements chemistry

  1. $Be{SO} _{4}$

  2. $Mg{SO} _{4}$

  3. $Ca{SO} _{4}$

  4. $Ba{SO} _{4}$

Show answer
Correct Option: B

Which of the following is INCORRECT statement:

some important compounds of magnesium and calcium the s-block elements chemistry

  1. Above 373 k,$Na _2CO _3,10H _2O$ converted into anhydrous form

  2. Hemihydrate of $CaSO _4$ is known as Gypsum

  3. $NaHCO _3$ act as weak antiseptic for skin infections

  4. All of these

Show answer
Correct Option: B
Explanation:

Gypsum is a hydrated calcium sulphate (CaSO4. 2H2O). Plaster of Paris is calcium sulphate hemihydrate. 

Solubility product of $\displaystyle { Mg\left( OH \right)  } _{ 2 }$ at ordinary temperature is $\displaystyle 1.96\times { 10 }^{ -11 }$. $\displaystyle pH$ of a saturated solution of $\displaystyle { Mg\left( OH \right)  } _{ 2 }$ will be

some important compounds of magnesium and calcium the s-block elements chemistry

  1. 10.53

  2. 8.47

  3. 6.94

  4. 3.47

Show answer
Correct Option: A
Explanation:

$\displaystyle { Mg\left( OH \right)  } _{ 2 }\rightleftharpoons M{ \underset { S }{ g }  }^{ 2+ }+2{ \underset { 2S }{ OH }  }^{ - }$
$\displaystyle { K } _{ sp }{ Mg\left( OH \right)  } _{ 2 }=\left[ { Mg }^{ 2+ } \right] { \left[ { OH }^{ - } \right]  }^{ 2 }$
$\displaystyle \Rightarrow \quad { K } _{ sp }{ Mg\left( OH \right)  } _{ 2 }=4{ S }^{ 3 }$
$\displaystyle 1.96\times { 10 }^{ -11 }=4{ S }^{ 3 }$
or $\displaystyle S={ \left[ \frac { 1.96\times { 10 }^{ -11 } }{ 4 }  \right]  }^{ 1/3 }$
or $\displaystyle S={ \left( 4.9\times { 10 }^{ -12 } \right)  }^{ 1/3 }$
$\displaystyle \therefore \quad S=1.69\times { 10 }^{ -4 }$
So, concentration of $\displaystyle \left[ { OH }^{ - } \right]=2S $
$\displaystyle \therefore \quad \left[ { OH }^{ - } \right] =3.38\times { 10 }^{ -4 }$
$\displaystyle \Rightarrow \quad pOH=-\log { \left[ { OH }^{ - } \right]  } $
$\displaystyle =-\log { \left[ 3.38\times { 10 }^{ -4 } \right]  } $
$\displaystyle \therefore \quad pOH=3.471$
$\displaystyle pH=14-pOH$
$\displaystyle =14-3.471$
$\displaystyle \therefore \quad pH=10.529$

$Mg+O _2\rightarrow\ ?$

some important compounds of magnesium and calcium the s-block elements chemistry

  1. $MgO$

  2. $MgO+O _2$

  3. $2MgO+O _2$

  4. none of the above

Show answer
Correct Option: A
Explanation:

The reaction between Mg and oxygen is as follow:

$2Mg+O _2\rightarrow\ 2MgO$

The tribasic form of calcium phosphate is ________ in water.

some important compounds of magnesium and calcium the s-block elements chemistry

  1. soluble

  2. insoluble

  3. sparingly soluble

  4. soluble only at high temperature

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Correct Option: B
Explanation:

Tricalcium phosphate (TCP) is a calcium salt of phosphoric acid with the chemical formula $Ca _3(PO _4) _2$. It is also known as tribasic calcium phosphate and bone phosphate of lime (BPL). It is a white solid, with very low solubility.

The major problem in the production of single superphosphate(SSP) is:

some important compounds of magnesium and calcium the s-block elements chemistry

  1. evolution of chlorine containing gases

  2. evolution of fluorine containing gases

  3. evolution of sulphur containing gases

  4. evolution of nitrogen containing gases

Show answer
Correct Option: B
Explanation:

The evolution of fluorine containing gases is a major problem in the SSP production process. Theese gases arise from the fluoride and silicon contained as impurities in the rock. These elements combine with the water to form flurosilic acid$ (H _2SiF _6). $ Any excess silicon dissolves (in acid) to form silicic acid $(SiO _2-H _2O).$Typical rock phosphate contains about 8% Silica and 3% Fluorine by weight.

Gypsum is found in mainly which kind of rocks?

some important compounds of magnesium and calcium the s-block elements chemistry

  1. Igneous

  2. Sedimentary

  3. Metamorphic

  4. All of these

Show answer
Correct Option: B
Explanation:

Gypsum or Calcium Sulphate dihydrate $CaSO _4.2H _2O$ is mostly found in beds of sedimentary rocks.