Tag: chemistry

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Multiple choice chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

According to adsorption theory of catalysis, the speed of reaction increases because:

  1. the concentration of the reactant molecules at the active centres of the catalyst becomes high due to adsorption

  2. in the process of adsorption, the activation energy of the molecules becomes large

  3. adsorption produces heat which increases the speed of the reaction

  4. adsorption lowers the activation energy of the reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to adsorption theory of catalysis, the speed of reaction increases because the concentration of the reactant molecules at the active centres of catalyst becomes high due to adsorption.

Hence option A is correct.

Multiple choice chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

According to the adsorption theory of catalysis,the speed of the reaction increase because :

  1. The concentration of reactant molecules at the active centers of the catalyst becomes high due to adsorption

  2. In the process of adsorption, the activation energy of the molecules becomes large

  3. Adsorption produces heat which increases the speed of the reaction

  4. Adsorption lowers the activation energy of the reaction.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The correct answer is $D$ . In the presence of catalyst the speed of reaction increases since the activation energy gets reduced and hence the rate of adsorption increases.

Multiple choice chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

Chlorophyll, the green colouring matter in plants helps the process of photosynthesis by:

  1. acting as a catalyst

  2. converting soil into carbohydrates

  3. reacting with carbon dioxide

  4. fixing soil nitrogen
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Chlorophyll plays a vital role by absorbing sunlight of a range of wavelengths, primarily blue and red. It is a catalyst for photosynthesis - increasing the speed of the reaction by taking part in it but remaining unchanged at the end.
Multiple choice chemistry adsorption and colloids adsorption theory of heterogeneous catalysis enzymes and catalysts catalysis

Match the reaction of Column - I with the catalysts in Column - II:

Column - I(Reaction) Column - II(Catalyst)
(a) $2KClO _3(s) \rightarrow 2KCl(s) +3O _2(g)$ (p) $Al _2O _3$
(b) $ 2SO _2(g) +O _2(g) \rightarrow 2SO _3(g)$ (q) $Pt$
(c) $2H _2O _2(l) \rightarrow 2H _2O(l) +O _2(g)$ (r) $V _2O _5$
(d) $ N _2(g) + 3H _2 (g) \rightarrow 2NH _3 (g)$ (s) $MnO _2$
  1. $a\rightarrow s,b\rightarrow r,c\rightarrow s,d\rightarrow p\ \& \ q$
  2. $a\rightarrow p,b\rightarrow r,c\rightarrow s,d\rightarrow p\ \& \ s$
  3. $a\rightarrow q,b\rightarrow r,c\rightarrow s,d\rightarrow q$
  4. $a\rightarrow s,b\rightarrow r,c\rightarrow q,d\rightarrow p\ \& \ q$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

a)  For $KClO _3$ decomposition Manganeese(IV) oxide is used as catalyst at an elevated temparature of 150 degree given by the formula $MnO _2$.


b) The catalyst that promotes the $SO _2$ oxidation at temparature of 500 degree where $SO _2$ is thermodynamically efficient is vanadium pentoxide given by $V _2O _5$.


c) The catalyst that provides alternative way with low activation energy  for decomposition of $H _2O _2$ is $MnO _2$.

d) Synthesis of Ammonia by Haber process uses $Pt$ and $Al _2O _3$ as a compromise catalysts in place of $Fe$.

Option A is correctt.

Multiple choice chemistry man made materials environmental impact: plastics plastic plastic plastic waste garbage in, garbage out

Which of the following is not a characteristic of thermosetting polymers?

  1. Linear or slightly branched long chain polymers.

  2. Heavily branched and cross-linked polymers.

  3. Become infusible on moulding.

  4. Cannot be remoulded or reused on heating.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Some characters of thermosetting polymers:

  • these polymers are cross-linked or heavily branched molecules,
  • on heating it undergoes extensive cross-linking in moulds and again become infusible,
  • these cannot be reused
    Some common examples are bakelite, melamine and urea formaldehyde resin

Multiple choice chemistry man made materials environmental impact: plastics plastic plastic plastic waste garbage in, garbage out

Which among the following is a cross-linked polymer?

  1. Polyesters

  2. Glycogens

  3. Melamine-formaldehyde

  4. Polyvinyl chloride
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Melamine-formaldehyde polymer is cross-linked polymer or thermosetting polymer which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins, etc.

The correct option is [C].

Multiple choice chemistry man made materials environmental impact: plastics plastic plastic plastic waste garbage in, garbage out

Which of the following polymers does not involve cross-linkages?

  1. Vulcanised rubber

  2. Bakelite

  3. Melamine

  4. Teflon
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Bakelite, melamine( thermosetting) and vulcanised rubber( elastomer) have cross-linkages in the structures whereas Teflon is linear addition or chain growth polymers that have not cross-linkages.

the correct option is [D].

Multiple choice chemistry man made materials environmental impact: plastics plastic plastic plastic waste garbage in, garbage out

Match the column I with column II and mark the appropriate choice.

Column I Column II
(A) Buna-S (i) Thermosetting
(B) Polyamides (ii) Fibres
(C) Polyvinyls (iii) Elastomers
(D) Urea-formaldehyde (iv) Thermoplastics
  1. (A) $\rightarrow$ (iv), (B) $\rightarrow$ (iii), (C) $\rightarrow$ (i), (D) $\rightarrow$ (ii)
  2. (A) $\rightarrow$ (ii), (B) $\rightarrow$ (i), (C) $\rightarrow$ (iii), (D) $\rightarrow$ (iv)
  3. (A) $\rightarrow$ (iii), (B) $\rightarrow$ (ii), (C) $\rightarrow$ (iv), (D) $\rightarrow$ (i)
  4. (A) $\rightarrow$ (i), (B) $\rightarrow$ (iv), (C) $\rightarrow$ (ii), (D) $\rightarrow$ (iii)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
 Buna$-S$  (iii) Elastomers
 Polyamides  (ii) Fibers
 Polyvinyls (iv) Thermoplastic
 Urea-formaldehyde (i) Thermosetting

[A] Elastomers - these are rubber like solids with elastic properties

[B] Fibers - these are thread forming solids which possess high tensile strength and high modulus,
[C] Thermoplastic - these are linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling,
[D] Thermosetting polymers are cross-linked and heavily branched molecules which on heating undergo extensive cross-linking in moulds and again become infusible.
The correct option is $[C]$.

Multiple choice chemistry man made materials environmental impact: plastics plastic plastic plastic waste garbage in, garbage out

Teflon is a special plastic on which oil and water do not stick.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Teflon is a synthetic polymer (polytetrafluoroethylene) that can be used to cover the surface of certain object and imparts nonstick properties to it. Teflon is used for Non Stick material because the monomer units are hydrophobic in nature (tetrafluoroethylene) and thus oil and water do not stick to it.
option A is correct.

Multiple choice chemistry man made materials environmental impact: plastics plastic plastic plastic waste garbage in, garbage out

Cooking pans have plastic handles.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Plastics are categorized into thermosoftening/thermoplastic and thermosetting/thermoset plastics.
In thermosoftening plastics, the forces between the polymer chains are weak, so they can easily be remoulded into new shapes. This makes it possible to recycle this type of plastic. whereas in thermosetting plastics there are strong covalent bonds forming cross-links between the polymer chains, making these plastics hard and rigid. Once set into its original shape, a thermosetting plastic can't be softened and remoulded. The strong bonds between polymers also mean that thermosetting plastics are much more heat resistant than thermosoftening ones.
Cooking pans' handle are made from thermosetting plastic like bakelite as this is resistant to heat.
option A is correct