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

Gypsum on heating to $300^{o}C$ gives:

  1. $CaSO _{4}2H _{2}O$
  2. $CaSO _{4}$
  3. $CaSO _{4}.\dfrac {1}{2}H _{2}O$
  4. $SO _{3}$ ans $CaO$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here answer is option C

Gypsum- chemical formula ;$Ca{ SO } _{ 4 }\cdot 2{ H } _{ 2 }O$
When gypsum is heated at 300K, we get plaster of paris(calcium sulphate hemihydrated salt)
$Ca{ SO } _{ 4 }\cdot 2{ H } _{ 2 }O\rightarrow Ca{ SO } _{ 4 }\frac { 1 }{ 2 } { H } _{ 2 }O+\frac { 3 }{ 2 } { H } _{ 2 }O$
Hence calcium sulphate Hemihydrated salt $Ca{ SO } _{ 4 }\frac { 1 }{ 2 } { H } _{ 2 }O$ is produced after heating gypsum.

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

$30\ g$ of Magnesium and $30\ g$ of oxygen are reacted, then the residual mixture contains:

  1. $50\ g$ of Magnesium oxide and $10\ g$ of oxygen
  2. $40\ g$ of Magnesium oxide and $20\ g$ of oxygen
  3. $45\ g$ of Magnesium oxide and $15\ g$ of oxygen
  4. $50\ g$ of Magnesium only
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
$2Mg+ { O } _{ 2 } \rightarrow 2 MgO$
According to the above reaction,
$28.6 g (2 mole)\ Mg$ combine with $32 g (1mole)$ of ${ O } _{ 2 }$ to give $80.6g(2mole)$ of MgO.
thus,
$30 g\ Mg$ will combine with $20 g$ of ${ O } _{ 2 }$ to produce $50 g\ MgO$ and $10 g$ ${ O } _{ 2 }$will remain unreactive.
Multiple choice some important compounds of magnesium and calcium the s-block elements chemistry

About $2.5\%$ gypsum $(CaSO _{4}.H _{2}O)$ is also added to cement as one of the consituents its function is to:

  1. Slow down the setting process to increase strength

  2. Speed the setting process to increase strength

  3. Absord moisture

  4. Make it anti-rusting
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Gypsum is a mineral and is hydrated calcium sulphate in chemical form. Gypsum plays a very important role in controlling the rate of hardening of the cement. During the cement manufacturing process, upon the cooling of clinker, a small amount of gypsum is introduced during the final grinding process.Gypsum is added to control the “setting of cement”. If not added, the cement will set immediately after mixing of water leaving no time for concrete placing.
conclusion: hence the option (A) is correct

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

A metal $M$ readily forms its sulphate $MSO _{4}$ which is water soluble. It forms its oxide $MO$ which becomes inert on heating. It forms an insoluble hydroxide $M(OH) _{2}$ which is soluble in $NaOH$ solution. Then M is:

  1. $Mg$
  2. $Ba$
  3. $Ca$
  4. $Be$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In the periodic table, on moving down, water solubility of alkaline earth metal decreases. Oxides and hydroxides of alkaline earth metal are basic except Be which is amphoteric.
Hence the metal M is Be.
conclusion: hence the option (D) is correct.

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

Several blocks of magnesium are fixed to the bottom of a ship to:

  1. make the ship lighter

  2. prevent action of water and salt

  3. prevent puncturing by under-sea rocks

  4. keep away the sharks
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Several blocks of magnesium are fixed to the bottom of a ship to. Magnesium, on account of its lightness, great affinity for oxygen and toughness is used in ship. Being a lighter element, magnesium makes the ship lighter when it is fixed to the bottom of the ship.

Hence option A is correct answer.

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

Dead burnt plaster is :

  1. ${ CaSO } _{ 4 }.{ 2H } _{ 2 }O$
  2. ${ MgSO } _{ 4 }.7{ H } _{ 2 }O$
  3. ${ CaSO } _{ 4 }.1/2{ H } _{ 2 }O$
  4. ${ CaSO } _{ 4 }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When Plaster of Paris $CaSO _4.\dfrac{1}{2}H _2O$ is heated above 393 K, its water of crystallisation is lost and anhydrous Calcium sulphate is left that is known as a dead burnt plaster.

Hence option D is correct answer.

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

When heated in steam, Mg burns brilliantly producing:

  1. $Mg(OH) _2$
  2. $MgO and H _2$
  3. $MgO and O _2$
  4. $MgO and O _3$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Magnesium burns in steam to produce white magnesium oxide and hydrogen gas. Very clean magnesium ribbon has a very slight reaction with cold water. After several minutes, some bubbles of hydrogen form on its surface, and the coil ofmagnesium ribbon usually floats to the surface.

The reaction occurs is,
$Mg+H _2O (g) \rightarrow MgO +H _2$

Hence option B is correct answer.