Tag: the s-block elements

Questions Related to the s-block elements

Magnesium metal is heated to redness in the presence of nitrogen and on cooling water is added. The gas evolved is:

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

  1. $N _{2}$

  2. $H _{2}$

  3. $NH _{3}$

  4. $O _{2}$

Show answer
Correct Option: C
Explanation:

The gas evolved is $NH _{3}$.

When magensium is heated to redness in the presence of nitrogen, it forms magnesium nitride.
$ 3Mg + N _{2} \rightarrow Mg _{3}N _{2}$

This magnesium nitride when reacts with water forms ammonia gas.
$Mg _{3}N _{2} + 6H _{2}O \rightarrow3Mg(OH) _{2} + 2NH _{3}$

The formula of anhydrite is:

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

  1. $CaSO _{4}.2H _{2}O$

  2. $2CaSO _{4}.H _{2}O$

  3. $CaSO _{4}$

  4. $Mg(ClO _{4}) _{2}$

Show answer
Correct Option: C
Explanation:

In nature, calcium sulphate occurs in the form of  anhydrite $(CaSO _4)$ and gypsum $(CaSO _4 \cdot 2H _2O)$.


Hence, option $C$ is correct.

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

Show answer
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

Show answer
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.