Tag: chemistry

Questions Related to chemistry

Which of the following compounds is known as epsom salt ?

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

  2. $MgSO _{4}.7H _{2}O$

  3. $FeSO _{4}.7H _{2}O$

  4. $Mg _{3}(PO _{4}) _{2}$


Correct Option: B
Explanation:

$Mg{ SO } _{ 4 }\cdot 7{ H } _{ 2 }O$ is also known as Epsom salt.

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 $CaO$


Correct Option: C
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.

$30\ g$ 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


Correct Option: A
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.

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


Correct Option: A
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

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. $Be$


Correct Option: D
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.

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


Correct Option: A
Explanation:

Several blocks of magnesium are fixed to the bottom of a ship toMagnesium, 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.

Gypsum is not chemically similar to:

  1. Selenite

  2. Alabaster

  3. Anhydrite

  4. Zlnorsper


Correct Option: D
Explanation:

Gypsum is calcium sulphate dihydrate $(CaSO _4 \cdot 2H _2O)$. Zlnorsper is not chemically similar to gypsum.

Potash magnerin is:

  1. $KCO _{ 3}.MgCO _{ 3} .5H _{2} O$

  2. $K _{2} SO _{4} .MgSO _{4} .6H _{2} O$

  3. $KCl.MgCl _{2} .6H _{2} O$

  4. none


Correct Option: B
Explanation:

The formula of Potash magnerin is $K _{2} SO _{4} .MgSO _{4} .6H _{2} O$

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. ${ CaSO } _{ 4 }$


Correct Option: D
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.

When heated in steam, Mg burns brilliantly producing:

  1. $Mg(OH) _2$

  2. $MgO and H _2$

  3. $MgO and O _2$

  4. $MgO and O _3$


Correct Option: B
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.