Tag: the s-block elements

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Questions Related to the s-block elements

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

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

  1. $N _{2}$
  2. $H _{2}$
  3. $NH _{3}$
  4. $O _{2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
$Mg _{3}N _{2} + 6H _{2}O \rightarrow3Mg(OH) _{2} + 2NH _{3}$

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

Magnesium may be called a refractory because it?

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.
Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

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

  1. $Mg(OH) _2$
  2. $BaSO _4$
  3. $Na _2CO _3$
  4. $Ba(OH) _2$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  1. $CaSO _4.1/2H _2O$
  2. $CaSO _4$
  3. $CaSO _4.H _2O$
  4. $2CaSO _4.3H _2O$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heating gypsum (CaSO4.2H2O) to 120 degrees Celsius drives off 1.5 molecules of water, resulting in Plaster of Paris, which is calcium sulfate hemihydrate (CaSO4.1/2H2O).

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

In aqueous solution, the most stable sulphate is :

  1. $Be{SO} _{4}$
  2. $Mg{SO} _{4}$
  3. $Ca{SO} _{4}$
  4. $Ba{SO} _{4}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Solubility of alkaline earth metal sulfates decreases down the group. Magnesium sulfate is highly soluble in water, making it the most stable in aqueous solution compared to the others which are less soluble or insoluble.

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

Which of the following is INCORRECT statement:

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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

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

  1. 10.53

  2. 8.47

  3. 6.94

  4. 3.47
Reveal answer Fill a bubble to check yourself
A Correct answer
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]  } $
$\displaystyle \therefore \quad pOH=3.471$
$\displaystyle pH=14-pOH$
$\displaystyle =14-3.471$
$\displaystyle \therefore \quad pH=10.529$

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

The tribasic form of calcium phosphate is ________ in water.

  1. soluble

  2. insoluble

  3. sparingly soluble

  4. soluble only at high temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
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.