Tag: chemistry

Questions Related to chemistry

Earlier, gramophone records were made from a natural resin, shellac, which comes from insects on trees. Nowadays, records lighter in weight are made from synthetic plastics like:

chemistry petrochemicals and polymers addition polymerisation types of polymerisation reactions polymer

  1. polyacrylonitrile

  2. PVC (or polyvinyl chloride)

  3. polythene

  4. bakelite

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Correct Option: B
Explanation:

They are made from PVC (or polyvinylchloride) because they are hard and non-breakable.

Which of the following polymers can be made by anionic addition polymerisation mechanism ?

chemistry petrochemicals and polymers addition polymerisation types of polymerisation reactions polymer

  1. PVC

  2. PAN

  3. Telfon

  4. PP

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Correct Option: A,B,C
Explanation:

Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of vinyl monomers with strong electronegative groups. This polymerization is carried out through a carbanion active species. 


Like all chain-growth polymerizations, it takes place in three steps: chain initiation, chain propagation and chain termination. 

Characteristics: In order for polymerization to occur with vinyl monomers, the substituents on the double bond must be able to stabilize a negative charge. Stabilization occurs through delocalization of the negative charge. The delocalisation of electron density can be done by Electron withdrawing group such as $CN$, $-F$, $-Cl$ etc.
The solvent is determined by the reactivity of both the initiator and carbanion of the propagating chain end.

Hence, polymers that can be made by anionic addition polymerisation mechanism are PVC, PAN and Teflon.

Monomer of $[NH - \overset{O}{\overset{||}{C}} - NH - CH _2] _n$ is :

chemistry petrochemicals and polymers addition polymerisation types of polymerisation reactions polymer

  1. Methanamine

  2. N-methyl urea

  3. Formaldehyde

  4. Ammonia

Show answer
Correct Option: C
Explanation:

Solution:- (C) Formaldehyde

It is urea formaldehyde polymer and it's monomers are urea and formaldehyde.

The main advantage of 'PVC' pipes for drainage is the feasibility of:

chemistry petrochemicals and polymers addition polymerisation types of polymerisation reactions polymer

  1. mechanical laying

  2. physical laying

  3. chemical laying

  4. both $B$ and $C$

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Correct Option: A

Which of the following alkenes is most reactive towards cationic polymerization?

chemistry petrochemicals and polymers addition polymerisation types of polymerisation reactions polymer

  1. ${ CH } _{ 2 }$ = ${ CHCH } _{ 3 }$

  2. ${ CH } _{ 2 }$ = $CHCl$

  3. ${ CH } _{ 2 }$ = ${ CHC } _{ 6 }{ H } _{ 5 }$

  4. ${ CH } _{ 2 }$ = ${ CHCOOCH } _{ 3 }$

Show answer
Correct Option: C
Explanation:

In cationic polymerization the most stable cation will show the highest reactivity.

The order of reactivity will be-

$CH _2 = CH-C _6H _5 > CH _2  = CHCH _3 > CH _2 = CHCl >CH _2 = CHCOOCH _3$

Option C is correct.

According to the law of triads :

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. the properties of the middle element were in between those of the other two members.

  2. three elements arranged according to increasing weights have similar properties.

  3. the elements can be grouped in the groups of six elements.

  4. every third element resembles the first element in periodic table.

Show answer
Correct Option: A
Explanation:

According to Dobereiner's law of triads, the properties of the middle element were in between those of the other two members. The elements were arranged in a group of three (called triads). The atomic weight of a middle element was almost the average of the other two. Three elements of the triad had similar chemical properties.

The law of triad is applicable to a group of :

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $Cl, Br, I$

  2. $C, N, O$

  3. $Na, K, Rb$

  4. $H, O, N$

Show answer
Correct Option: A,B
Explanation:

For Dobereiner's triads, the atomic weight of middle element is almost average of other two. Thus, the law of triad is applicable to (1) $Cl, Br, I$ and (2) $C, N, O$. However, it is not applicable to (3) $Na, K, Rb$ and (4) $H, O, N$. 


(1) For $Cl, Br$ and $I$, $\displaystyle \dfrac {35.5+127}{2} = 81.25 \simeq 80$ 


(2) For $C, N, O$ $\displaystyle \dfrac {12+16}{2}=14$ 

(3) For $Na, K, Rb$ $\displaystyle \dfrac {23+85.5}{2}=54.25 \neq 39$ 

(4) For $H,O,N$ $\displaystyle \dfrac {1+14}{2}=7.5 \neq 14$

In Doberenier triads, the atomic weights of the elements in a triad are in increasing order.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

True, atomic weight of the element in a Doberenier traid is in increasing order. Example: LI, Na, and K with atomic weight 6, 23, and 39 respectively.

Example of Dobereiner's triad is _________.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $Li , Al , Ca$

  2. $Li , Na , K$

  3. $Li , K , Na$

  4. $K , Al , Ca$

Show answer
Correct Option: B
Explanation:

$Li,Na,K$ is the example of Dobereineer's traid. Here, average of atomic weights of  'Li' and 'K' equals atomic weight of 'Na'.


$\dfrac{Weight\ of\ Li+ weight\ of\ K}{2}$ =$\dfrac{7+39}{2}$ =$\dfrac{46}{2}$ =23


=weight of $Na$.

The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. Such an arrangement of elements called as :

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. Dobereiner triad.

  2. Mendeleev triad.

  3. Modern triad.

  4. none of the above.

Show answer
Correct Option: A
Explanation:

Dobereiner observed in few atoms that mass of one atom is equal to the average of two atoms. He defined almost all properties basing on atomic weight.Later on it was proved wrong any-ways. Hence, this is called Dobereiner triad. Lithium has 7, sodium has 23 where as potassium has 39 as atomic masses.
$ 23 = (7+39)/2 = 23$

Here, we could observe that sodium atomic mass is average of potassium and lithium masses.