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Multiple choice limestone uses of group 2 compounds group 2 industrial inorganic chemistry chemistry

Nuclear attraction is often the deciding control factor for the association of natural molecules to
a given metal ion. Which one of the following represents the correct order of stability of the ions?
$[Be(H _2O) _4]^{2+} , [Mg(H _2O) _4]^{2+} , Ca(H _2O) _4]^{2+} and          Sr(H _2O)^4]^{2+}$

  1. $[Be(H _2O) _4]^{2+} > Sr(H _2O) _4]^{2+}] > [Mg(H _2O) _4]^{2+} > [Ca(H _2O)^4]^{2+}$
  2. $[Ca(H _2O) _4]^{2+} > [Mg(H _2O) _4]^{2+} > [Be(H _2O) _4]^{2+} > Sr(H _2O) _4]^{2+}$
  3. $[Sr(H _2O) _4]^{2+} > [Ca(H _2O) _4]^{2+} > [Mg(H _2O) _4]^{2+} > [Be(H _2O) _4]^{2+}$
  4. $[Be(H _2O) _4]^{2+} > [Mg(H _2O) _4]^2 > [Ca(H _2O) _4]^{2+} > Sr(H _2O) _4]^{2+}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The degree of hydration and the amount of hydration energy decreases as the size of the ion increases from   Be^{2+} to Sr^{2+}. 

                      $Be^{2+}       <      Mg^{2+}     <    Ca^{2+}    <     Sr^{2+}$

Hydration   -2494        - 1921          -1577         -1443 

Ergy (kJ moI$^{-1})$ 

Thus, stability of hydrated ion is 

$[Be(H _2O) _4]^{2+} >[Mg(H _2O _4]^{2+} > [Ca(H _2O) _4]^{2+} > [Sr(H _2O) _4]^{2+}$
Multiple choice limestone uses of group 2 compounds group 2 industrial inorganic chemistry chemistry

Based on the following analytical data, answer the given question.
A mineral, which can be represented by the formula $Mg _xBa _y(CO _3) _2$, was analyzed as described below:

A sample of the mineral was dissolved in excess hydrochloric acid and the solution made up to $100 cm^3$ with water. During the process, $48 cm^3$ of carbon dioxide, measured at $25^{\circ}C$ and 1-atmosphere pressure, were evolved.
A $25.0 cm^3$ portion of the resulting solution required $25.0 cm^3$ of EDTA solution of concentration $0.02 \ mol / dm^3$ to reach an end-point. A further $25.0 cm^3$ portion gave a precipitate of barium sulphate of mass 0.058 g on treatment with excess dilute sulphuric acid. You may assume that group-2 metal ions form 1:1 complexes with EDTA. Molar volume of any gas at $25^{\circ}C$ and 1 atmosphere pressure $ = 24 dm^3$).

The formula of the mineral is: 

  1. $MgBa(CO _3) _4$
  2. $MgBa(CO _3) _2$
  3. $MgBa(CO _3) _3$
  4. $Mg _2Ba(CO _3) _4$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The formula of the mineral is $MgBa(CO _3) _2$.

$48 cm^3$ of carbon dioxide corresponds to 0.002 moles.
Thus, $MgBa(CO _3) _2$ reacts with excess HCl to give 0.002 moles of carbon dioxide.

So $100.0cm^3$ solution will give 0.002 moles of carbon dioxide.
$25.0cm^3$ solution will give 0.0005 moles of carbon dioxide.

A $25.0cm^3$ portion of the resulting solution required $25.0cm^3$ of EDTA solution of concentration $0.02mol.dm^{-3}$ to reach an end-point.

Thus $25.0cm^3$ portion of the resulting solution contains $0.02 \times \frac {25.0}{1000}=0.0005 mol$ of metal ions.

A further $25.0cm^3$ portion gave a precipitate of barium sulphate of mass 0.058 g on treatment with excess dilute sulphuric acid.

0.058 g of barium sulphate corresponds to $\frac {0.058 g}{233.43  g/mol}=0.00025\  mol$.

$\therefore $  Moles of $Ba^{2+}$ ion $=$ Moles of $Mg^{2+}$ ion $=0.00025\ mol$  

So, formula of the compound is $MgBa(CO _3) _2$.

Multiple choice chemistry changes around us can all changes be reversed? substances and objects classification of changes

 Iron adopts changes slowly and gradually by process of :

  1. rusting

  2. moldings

  3. fermentation

  4. explosions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Iron adopt changes slowly and gradually when it comes in contact with air (moisture, oxygen etc)
When Iron reacts with $'n'$ molecules of water in the pressure of oxygen, it forms rust. Hence the process is known as a rusting.
$4Fe+3{ O } _{ 2 }+2n{ H } _{ 2 }O\longrightarrow 2{ Fe } _{ 2 }{ O } _{ 3 }.n{ H } _{ 2 }O$
Multiple choice chemistry changes around us can all changes be reversed? substances and objects classification of changes

 Burnt sparklers and burnt books pages are examples of 

  1. reversible change

  2. irreversible change

  3. no change

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Burnt sparklers and burnt books pages are examples of irreversible changes, as they are permanent changes which cannot be undone. Once these materials are burnt in to ashes, the original materials cannot be recovered back.

Multiple choice chemistry changes around us can all changes be reversed? substances and objects classification of changes

Which of the following is not a reversible change?

  1. Heating of water to steam

  2. Cooking of egg to scrambled eggs

  3. Heating of wax to molten wax

  4. Cooling a cake
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A reversible change can be undone to return to the original state. Cooking an egg involves chemical changes that permanently alter the proteins, making it irreversible.

Multiple choice chemistry changes around us can all changes be reversed? substances and objects classification of changes

Which of the following change cannot be reversed ?

  1. Hardening of cement

  2. Freezing of ice cream

  3. Opening a door

  4. Melting of choclate
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A reversible change is a physical change that can be undone. 
A final substance can be converted back to the original substance without creating any new material.
An irreversible change is a permanent change that cannot be undone.


A. Hardening of cement is an irreversible change as we cannot reverse back to the original cement powder form once the cement hardens.
B. Freezing of ice-cream is reversible change as it can be reversed back by heating and it will convert to original form.
C. Opening of a door is reversible change as it can be reversed simply by closing the door 
D. Melting of chocolate is reversible change as it can be reversed by cooling the chocolate to its original form.
Option A is the correct answer.

Multiple choice chemistry changes around us can all changes be reversed? substances and objects classification of changes

Burnt sparklers and burnt books pages are examples of:

  1. reversible process

  2. irreversible process

  3. rusting

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Irreversible changes $-$ because when they are burnt formation of gas and ashes takes place i.e. chemical reaction is taking place and new substance are formed which can't be reversed back.


      Book pages  $\quad \xrightarrow { \text{burning} } \quad { CO } _{ 2 }+$ other substances.

Hence, the correct option is $\text{B}$