Tag: chemistry

Questions Related to chemistry

In the process of vulcanization:

chemistry manmade materials synthetic rubber rubber polymer

  1. natural rubber is heated with sulphur

  2. natural rubber is heated with carbon

  3. natural rubber is heated with phosphorous

  4. natural rubber is heated with sodium

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Correct Option: A
Explanation:

Vulcanization is a chemical process by which the physical properties of natural or synthetic rubber are improved. In its simplest form, vulcanization is brought about by heating rubber with sulfur.

Which material is used for vulcanisation of rubber?

chemistry manmade materials synthetic rubber rubber polymer

  1. Iron

  2. Sulphur

  3. Chlorine

  4. Calcium Carbonate

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Correct Option: B
Explanation:

The material used for the vulcanisation of rubber is sulphur.


The reasons why the rubber is vulcanised are as follows:

i) It is soft and sticky and becomes more so at high temperature and brittle at low temperature. That is why, it is used at low-temperature range ($280-330$) K, where its elasticity is maintained.
ii) It is attacked by oxygen and other oxidising agents.
iii) It has a high water absorption capacity, low tensile strength and low resistance to abrasion.
iv) It is reactive to organic solvents.
Therefore, natural rubber is vulcanised by heating it with about ($3-5\%$) sulphur at ($373-415$) K.

Strength of synthetic fibre is better during-

chemistry manmade materials synthetic rubber rubber polymer

  1. dry condition

  2. wet condition

  3. humid condition

  4. never

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Correct Option: A

Which of the following type of forces are present in vulcanized rubber?

chemistry manmade materials synthetic rubber rubber polymer

  1. Weakest intermolecular forces

  2. Hydrogen bonding

  3. Three dimensional network of bonds

  4. Metallic bonding

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Correct Option: A
Explanation:

Vulcanised rubber is highly elastic, so weakest intermolecular forces present in it.

Which of the following is resistant to petrol, lubricating oils and organic solvents?

chemistry manmade materials synthetic rubber rubber polymer

  1. Nitrile rubber

  2. Buna - N

  3. GRN

  4. All of these

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Correct Option: D

A : A mixture of raw rubber and sulphur on heating at $373:K$ - $415:K$ gives vulcanised rubber.
R : ZnO decreases the rate of vulcanisation of rubber.

chemistry manmade materials synthetic rubber rubber polymer

  1. both A and R are correct and R is the correct explanation of the A

  2. both A and R are correct but R is not the correct explanation of the A

  3. A is correct but R is incorrect

  4. A is incorrect but R is correct

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Correct Option: C
Explanation:
Natural rubber becomes soft at high temperature (>335 K) and brittle at low temperatures (<283 K) and shows high water absorption capacity. It is soluble in non-polar solvents and is non-resistant to attack by oxidising agents. 

To improve upon these physical properties, a process of vulcanisation is carried out. This process consists of heating a mixture of raw rubber with sulphur and an appropriate additive at a temperature range between 373 K to 415 K. On vulcanisation, sulphur forms cross links at the reactive sites of double bonds and thus the rubber gets stiffened.

In sulfur vulcanization of natural rubber, the types of cross-links formed largely depend on the vulcanization system. The vulcanizing agents are zinc oxide (ZnO), stearic acid, accelerators, and sulfur. Conventional ZnO, or micro ZnO, is one of the basic components of rubber compounds and acts as an activator for rubber crosslinking by sulfur or sulfur donors.

Hence, reason given is incorrect. So, option C is correct.

Assertion (A) : The plants yield a milky suspension of crude rubber called latex.
Reason (R) : The latex contains about $85\%$ rubber.

chemistry manmade materials synthetic rubber rubber polymer

  1. Both A and R are correct and R is the correct explanation of the A

  2. Both A and R are correct but R is not the correct explanation of the A

  3. A is correct but R is incorrect

  4. A is incorrect but R is correct

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Correct Option: C
Explanation:
The plants yield a milky suspension of crude rubber called latex.
Latex is often described as the sap of the Hevea tree, a milky sticky substance. 

The sap runs deeper inside the tree, beneath the cambium.
Latex runs in the latex ducts which are in a layer immediately outside the cambium. This highlights the skill of the tapper. 

If the cambium is cut, then the tree is damaged because the cambium is where all the growth takes place.

The latex contains about $60\%$ of rubber and $40\%$ of other substances (water, proteins etc).


Assertion (A) is correct. Reason (R) is incorrect. Option C is correct.

Acetaldehyde can be used for making synthetic:

chemistry manmade materials synthetic rubber rubber polymer

  1. protein

  2. perfumes

  3. rubbers

  4. sugar

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Correct Option: C
Explanation:

Acetaldehyde is primarily used as an intermediate in the manufacture of a range of chemicals, perfumes, aniline dyes, plastic and synthetic rubber, etc.

$\therefore$ Answer is option $B$ and $C$.

Which of the following is not a synthetic rubber?

chemistry manmade materials synthetic rubber rubber polymer

  1. Neoprene

  2. Buna-N rubber

  3. Buna-S rubber

  4. Polyethylene

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Correct Option: D

The equilibrium constant $K p$ for the reaction $2H _2(g) + O _2(g)  \rightleftharpoons 2H _2O(g)$ at 2000 K is $1.6 \times 10^7$. The equilibrium constant of the reaction $H _2O(g)  \rightleftharpoons H _2(g) + \frac{1}{2} O _2(g)$ is _______.

chemistry chemical equilibrium relationship between equilibrium constant, reaction quotient and gibbs energy law of mass action chemical equilibrium and acids-bases

  1. $6.25 \times 10^{-8}$

  2. $2.5 \times 10^{-4}$

  3. $7.5 \times 10^{-12}$

  4. $4\times 10^{-6}$

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Correct Option: B
Explanation:

For the reaction, $2H _2(g) + O _2(g)  \rightleftharpoons 2H _2O(g)$,
$K = \dfrac{{[H _2O]}^{2} _{}} {{[H _2]}^{2} _{} [{O} _{2}]}$

$2H _2O(g)  \rightleftharpoons 2H _2(g) + O _2(g)$
$K = \dfrac{{[H _2]}^{2} _{} [{O} _{2}]}{[{H _2O}]^{2} _{}}$

$H _2O(g)  \rightleftharpoons H _2(g) + \frac{1}{2} O _2(g)$
$K _1 = \sqrt{\dfrac{{[H _2O]}^{2} _{}} {{[H _2]}^{2} _{} [{O} _{2}]}}$

Thus, $K _1 = \dfrac{1}{\sqrt{1.6107}}$$= 2.5 \times 10^{-4}$