Tag: chemistry

Questions Related to 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?
$[Be(H _2O) _4]^{2+} , [Mg(H _2O) _4]^{2+} , Ca(H _2O) _4]^{2+} and          Sr(H _2O)^4]^{2+}$

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

  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. $[Be(H _2O) _4]^{2+} > [Mg(H _2O) _4]^2 > [Ca(H _2O) _4]^{2+} > Sr(H _2O) _4]^{2+}$

Show answer
Correct Option: D
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 

$[Be(H _2O) _4]^{2+} >[Mg(H _2O _4]^{2+} > [Ca(H _2O) _4]^{2+} > [Sr(H _2O) _4]^{2+}$

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: 

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

  1. $MgBa(CO _3) _4$

  2. $MgBa(CO _3) _2$

  3. $MgBa(CO _3) _3$

  4. $Mg _2Ba(CO _3) _4$

Show answer
Correct Option: B
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 $MgBa(CO _3) _2$.

All chemical reactions are :

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

  1. reversible

  2. irreversible

  3. exothermic

  4. endothermic

Show answer
Correct Option: B
Explanation:

A change in which one or more than one new substances are formed is known as a chemical change. 


A chemical change is also called a chemical reaction. Chemical reactions are not reversible.

Hence the option B is correct.

Sheet erosion is due to _________.

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

  1. fast running rivers

  2. heavy rains

  3. occasional rains

  4. wind

Show answer
Correct Option: B
Explanation:

Sheet erosion is the detachment of soil particles by raindrop impact and their removal downslope by water flowing overland as a sheet instead of in a definite channel.


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

Which of the following changes are irreversible?

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

  1. Milk to paneer

  2. Cow dung to biogas

  3. Grain to its flour

  4. All of the above

Show answer
Correct Option: D
Explanation:

All of the following changes are irreversible because we can not convert the product into reactant again.
1) Milk to paneer.
2) Cow dung to biogas.
3) Grain to its flour.

 Iron adopts changes slowly and gradually by process of :

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

  1. rusting

  2. moldings

  3. fermentation

  4. explosions

Show answer
Correct Option: A
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.
$4Fe+3{ O } _{ 2 }+2n{ H } _{ 2 }O\longrightarrow 2{ Fe } _{ 2 }{ O } _{ 3 }.n{ H } _{ 2 }O$

 Burnt sparklers and burnt books pages are examples of 

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

  1. reversible change

  2. irreversible change

  3. no change

  4. none of the above

Show answer
Correct Option: B
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.

Which of the following is not a reversible change?

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

  1. Heating of water to steam

  2. Cooking of egg to scrambled eggs

  3. Heating of wax to molten wax

  4. Cooling a cake

Show answer
Correct Option: B

Which of the following change cannot be reversed ?

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

  1. Hardening of cement

  2. Freezing of ice cream

  3. Opening a door

  4. Melting of choclate

Show answer
Correct Option: A
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.

Burnt sparklers and burnt books pages are examples of:

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

  1. reversible process

  2. irreversible process

  3. rusting

  4. none of these

Show answer
Correct Option: B
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 $\text{B}$