Tag: chemistry

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Questions Related to chemistry

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

Which of the following is thermosetting polymer?

  1. Nylon

  2. Sealing wax

  3. Polysiloxanes

  4. Both B and C
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Thermosetting polymers: These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are polysiloxanes, bakelite, urea- formaldehyde resins, etc.

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

Three-dimensional molecules with cross-links are formed in the case of a:

  1. thermosetting plastic

  2. thermoplastic

  3. both (a) and (b)

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Thermosetting plastic consists of chain of the  molecules which are cross-linked, with each other when heated. When thermosetting plastics cross-link, the molecules create a permanant, network  which is a $3-D$ structure and can be considered one giant molecule. Once cured, thermosetting plastic cn not be remelted, in the same way that cured concrete cannot be reset. 

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

Garden chairs made of plastic strips and plastic articles get faded, worn out and cracked in sunlight, mainly because of:

  1. Low melting point of plastic

  2. Ultraviolet rays

  3. Heat

  4. The red colour
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Garden chairs made of plastic strips and plastic articles get faded, worn out and cracked in sunlight, mainly because of UV rays. All types of UV can cause a photochemical effect within the polymer which can lead to degradation of some sort to the materials. Absorbed UV energy can exits the photon in a plastic, exciting the photons can create free radicals. Those free radicals can cause breaks in the polymer bonds.

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

Which of the following are not thermosetting polymers ?

  1. Bakelite

  2. polystyrene

  3. PVC

  4. Melmac
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

Thermosetting polymers have different properties to thermosoftening polymers. Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily.


Examples are given below:
  • Polyester fibreglass systems: sheet molding compounds and bulk molding compounds
  • Polyurithane insulating foams, mattresses, coatings, adhesives, car parts, print rollers, shoe soles, flooring, synthetic fibers, etc. Polyurethane polymers are formed by combining two bi- or higher functional monomers/oligomers.
  • Vulcanized rubber
  • Bakelite, a phenol formaldehyde resin used in electrical insulators and plasticware
  • Duroplast, light but strong material, similar to bakelite used for making car parts


Polyvinyl chloride(PVC) and polystyrene are thermoplastic polymer.
Hence, options B and C are correct.

Multiple choice chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

In Newland's classification, elements are arranged in an increasing order of their:

  1. mass number

  2. atomic number

  3. atomic weight

  4. all of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Newlands arranged elements in increasing order of their atomic weight and stated that every eighth element resembled properties of first element. This is Newland's law of Octaves. Hence correct answer for asked question is option C-atomic weight.

Multiple choice chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

Which of the following is the correct set of elements to Dobereiner's triads ?

  1. Li - 7, Na - 23, K -39

  2. Br - 80, Cl - 35.5, I - 127

  3. Fe - 55.85, Ni - 58.71, Co - 58.93

  4. All of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Dobereiner's triads are a group of three elements in which the atomic mass of the middle element is equal to the average of atomic masses of the first and the third element.


For option A,
Average of atomic masses of first and last elements = $7+ \dfrac{39}{2} = 23$
This is the atomic mass of second element.

For option B.
Average of atomic masses of first and last elements = $80+ \dfrac{127}{2} = 103.5$
This is not the atomic mass of the second element.

For option C,
Average of atomic masses of first and last elements = $55.85+ \dfrac{58.93}{ 22} = 55.89$
This is not the atomic mass of the middle element.

Hence, the correct answer is option $A$.

Multiple choice chemistry classification of elements- the periodic table development of the modern periodic table into the history mendeleef's periodic table

The first attempt to classify elements systemically was made by :

  1. Mendeleev

  2. Newland

  3. Lother Meyer

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

The first attempt to classify elements systemically was made by Dobereiner.
The triads of elements that showed similar chemical properties.
Other properties of the elements followed trends in which the value of the middle element of the triad was in between those of the end members.

Multiple choice chemistry classification of elements- the periodic table development of the modern periodic table into the history mendeleef's periodic table

The arrangement of elements in a group of three is known as Law of Triads.

  1. True

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

Johann Wolfgang Dobereiner proposed the Law of Triads, which grouped elements with similar properties into sets of three where the atomic mass of the middle element was approximately the average of the other two.

Multiple choice chemistry periodic table development of the modern periodic table into the history mendeleef's periodic table

Statement: In Dobernier classification of elements, the atomic weight of the middle element is equal to the average of the extreme elements of a triad.


State whether the given statement is true or false.

  1. True

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

Dobereiner classified the elements into triads (group of three). He made the groups such that, the mass of middle element is the average of the mass of other $2$ elements. This is Dobernier's law of triads. 


Thus given statement is $\text{true}$.

Multiple choice chemistry classification of elements- the periodic table development of the modern periodic table into the history mendeleef's periodic table

The atomic masses of Li and K are 7 and 39, respectively. According to law of triads the atomic mass of Na will be:

  1. 23

  2. 32

  3. 46

  4. 64
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Dobereiner arranged the elements in increasing order of atomic masses. He found that the atomic mass of the middle element was approximately equal to the arithmetic mean (average) of the atomic masses of the other two elements of that triad when they are arranged in their increasing order of atomic mass.

So Li=7,K=39

Atomic mass of Na = $\dfrac{7+39}{2}=\dfrac{46}{2}=23$