Tag: some important compounds of magnesium and calcium

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

Which of the following form is the soluble form of calcium phosphate?

  1. Monobasic form

  2. Tribasic form

  3. Both

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Monocalcium phosphate is an inorganic compound with the formula $Ca{(H _2PO _4)} _2$. It is commonly found as the monohydrate $Ca{(H _2PO _4)} _2.H _2O$. Both salts are colourless solids. They are used mainly as water soluble superphosphate fertilisers.

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

How is Calcium Sulphate produced from Calcium Oxide?

  1. $CaO$ $+$ $H _2SO _4$
  2. $CaO$ $+$ $SO _2$
  3. $CaO$ $+$ $SO _3$
  4. $CaO$ $+$ $S$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Calcium sulphate can be produced from Calcium oxide by reacting it with Sulphuric acid. The reaction can be written as-
$CaO$ $+$ $H _2SO _4$ $=$ $CaSO _4$ $+$ $H _2O$

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

In which of following cases is the value of x maximum?

  1. $CaSO _4,xH _2O$
  2. $BaSO _4,xH _2O$
  3. $MgSO _4,xH _2O$

  4. All have the same value of x
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$MgSO _4$ has 7 moles of water of hydration.
$CaSO _4$ has 2 moles of water hydration $BaSO _4$ has 1 mole of water of hydration.
Thus $MgSO _4$ has maximum x.

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

Choose the correct answer from the alternatives given.
Dead burnt plaster is :

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

Anhydrous calcium sulphate, CaSO$ _4$ is known as 'dead burnt plaster'. It is formed by heating gypsum, $CaSO _4.2H _2O$ at a temperature above 393 K.

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

Gypsum is added to cement to:

  1. make the mixture more homogeneous

  2. improve the texture of cement

  3. make the cement light weight

  4. delay the setting time of cement
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The purpose of adding gypsum is only to slow down the process of setting of the cement so that it gets sufficiently hardened.

Hence, gypsum is added to cement to delay the setting time of cement.

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