Chemistry Questions

Q:

Which of the following is the strongest base?

A) LiCH3 B) LiF
C) LiOH D) LiNH2
 
Answer & Explanation Answer: A) LiCH3

Explanation:

The stability of the ions is determined by the energy of the lone pairs. Carbon has the least effective nuclear charge (Zeff) and so the lone pair on the CH3− ion has the highest energy, making it the least stable ion and so the strongest base. The Zeff increases as we move across the period until we get to fluorine which has the greatest Zeff and so its lone pairs have the lowest energy, making F− the least basic ion.

 

In order of decreasing basicity they are ranked LiCH3 > LiNH2 > LiOH > LiF. We are dealing with the ions F−, OH−, NH2− and CH3− and so the factor which influences their basicity is the stability of the ion compared to its conjugate acid.

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Q:

The magnetic moment (spin only) of  [NiCl4]2-is

A) 1.41 BM B) 1.82 BM
C) 5.46 BM D) 2.82 BM
 
Answer & Explanation Answer: D) 2.82 BM

Explanation:

Hybridisation of Ni is e-  

Unpaired 3d8in  is 2 

So Ω = n(n+2)BM=2x4 = 8 = 2.82BM

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Q:

Which of the following processes is used to remove reducible oxides from the metal?

A) liquation B) cupellation
C) poling D) electro refining
 
Answer & Explanation Answer: C) poling

Explanation:
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Q:

Order of basicity of amines in gaseous state?

A) 2'> 1'> 3' > NH3 B) 3' > 2' > 1'> NH3
C) 1' > 2' > 3'> NH3 D) 2'> 3'> 1' > NH3
 
Answer & Explanation Answer: B) 3' > 2' > 1'> NH3

Explanation:

The order of basicity in ammonia is different in gaseous phases vs. aqueous phases due to hydrogen bonding.

 

So in gaseous phases it's the well known: 3' > 2' > 1'> NH3. Just so we're on the same page, this is due to the inductive effect of electron donating alkyl groups--they destabilize the lone pair on nitrogen atom, making nitrogen more basic.

 

But in aqueous phase, the order is slightly different: 2'> 1'> 3' > NH3.

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Q:

In photography, the compound of nitrogen used is 

A) Potassium nitrate B) Silver nitrate
C) Ammonium carbonate D) Ammonium bicarbonate
 
Answer & Explanation Answer: B) Silver nitrate

Explanation:

Silver nitrate is the basic substance from which silver bromide is obtained. The photographic films are impregnated with the light sensitive AgBr.

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Q:

What are the reactants in a chemical reaction?

Answer

In a chemical reaction, substances (elements or compounds) called reactants are changed into other substances (compounds or elements) called products. Hence, reactants are those which start the chemical reaction.


 


For example:


1. In the burning of natural gas, methane (CH4) and oxygen (O2) are the reactants in the chemical reaction. are the substances formed by a chemical reaction. In the burning of natural gas, carbon dioxide (CO2) and water (H2O) are the products formed by the reaction.


 


2. H2+O2 ----> H2O


Here H2 & O2 are called Reactants and H2O is called Product.


 

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Q:

The reactivity of an atom arises from 

A) the existence of unpaired electrons in the valence shell B) the energy differences between the electron shells
C) the sum of the potential energies of all the electron shells D) the average distance of the outermost electron shell from the nucleus
 
Answer & Explanation Answer: A) the existence of unpaired electrons in the valence shell

Explanation:

When atoms react they do so in order to reach the lowest energy, which is the most stable. The electrons orbitals will overlap in the way that reduces the energy the most. Orbitals of similar energy will produce the greatest stabilisation.The answer you gave isn't the whole story, it depends what species is reacting with what. The effective nuclear charge on the atom will affect the energy of the valance electrons.

 

Hence, the reactivity of an atom arises from the existence of unpaired electrons in the valence shell.

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Q:

Natural radioactivity was discovered by

A) Rutherford B) Becquerel
C) Curie D) Schmidt
 
Answer & Explanation Answer: B) Becquerel

Explanation:
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