Chemistry 7 Solved Past Papers 2025 – 2025 Archives

Industrial Chemistry Past Papers

Solved past paper MCQs for Industrial Chemistry from official UHS, NUMS, SZABMU, DUHS, and KMU examinations. Includes verified distractor autopsies and step-by-step cognitive explanations.

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#1 of 7 Sindh MDCAT 2025
[Sindh MDCAT 2025]

Which of following adhesive is used to bond broken pieces of jewelry?
A
Epoxy resin
B
Super glue
C
Silicon resin
D
Starch
View Answer & Propolis Autopsy
Correct Key: Option B Diagnostic Explanation
Concept:

Cyanoacrylate adhesives (commonly known as super glue) undergo rapid anionic polymerization in the presence of trace moisture, forming high-strength bonds between non-porous surfaces.

Formula / Reaction:

$$n\,\text{CH}_2=\text{C}(\text{CN})\text{COOCH}_3 + \text{H}_2\text{O (trace)} \longrightarrow -[\text{CH}_2-\text{C}(\text{CN})(\text{COOCH}_3)]_n-$$

Solution:

  • Super glue is specifically formulated for fast, rigid bonding of non-porous materials such as metals, glass, ceramics, and jewelry.


  • It cures within seconds at room temperature without requiring mixing or external heat.


Why other options are incorrect:

  • Epoxy resin: Requires manual mixing of resin and hardener and exhibits a longer curing time, making it less convenient for delicate jewelry repairs.


  • Silicon resin: Forms flexible, elastomeric joints that lack the rigid shear strength required for fine metal and gemstone settings.


  • Starch: A weak, water-soluble natural adhesive used primarily for paper products.
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#2 of 7 Sindh MDCAT 2025
[Sindh MDCAT 2025]

Which one is addition polymer?
A
nylon 6,6
B
nylon 6,10
C
polyvinyl chloride
D
polyester
View Answer & Propolis Autopsy
Correct Key: Option C Diagnostic Explanation
Concept:

Addition (chain-growth) polymers are formed by the successive addition of unsaturated monomer units across double or triple bonds without the elimination of any small by-product molecules.

Formula / Reaction:

$$n\,\text{CH}_2=\text{CH}-\text{Cl} \xrightarrow{\text{Initiator}} -[\text{CH}_2-\text{CH}(\text{Cl})]_n-$$

Solution:

  • Polyvinyl chloride (PVC) is produced by the free-radical addition polymerization of vinyl chloride (chloroethene).


  • The empirical formula of the polymer repeating unit is identical to that of the monomer, confirming addition polymerization.


Why other options are incorrect:

  • nylon 6,6: A condensation polyamide synthesized from hexamethylenediamine and adipic acid with elimination of \(\text{H}_2\text{O}\).


  • nylon 6,10: A condensation polyamide formed from hexamethylenediamine and sebacoyl chloride/sebacic acid.


  • polyester: A condensation polymer formed between diols and dicarboxylic acids with elimination of \(\text{H}_2\text{O}\).
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#3 of 7 Balochistan MDCAT 2025
[Balochistan MDCAT 2025]

Which monomer is used for synthesis of nylon 6,6?
A
Hexamethylene diamine
B
Sobacoyl chloride
C
Methylene diamine
D
Heptane-1, 7-dioic acid
View Answer & Propolis Autopsy
Correct Key: Option A Diagnostic Explanation
Concept:

Nylon-6,6 is a synthetic polyamide formed via step-growth condensation polymerization of a six-carbon diamine with a six-carbon dicarboxylic acid.

Formula / Reaction:

$$n\,\text{H}_2\text{N}-(\text{CH}_2)_6-\text{NH}_2 + n\,\text{HOOC}-(\text{CH}_2)_4-\text{COOH} \longrightarrow -[\text{HN}-(\text{CH}_2)_6-\text{NH}-\text{CO}-(\text{CH}_2)_4-\text{CO}]_n- + 2n\,\text{H}_2\text{O}$$

Solution:

  • The monomers required for Nylon-6,6 are hexamethylenediamine (1,6-diaminohexane) and adipic acid (hexanedioic acid).


  • The designation '6,6' denotes that both reacting monomer species contain exactly 6 carbon atoms.


Why other options are incorrect:

  • Sobacoyl chloride: A 10-carbon acyl chloride monomer used in the synthesis of Nylon-6,10.


  • Methylene diamine: Contains only 1 carbon atom and does not form Nylon-6,6.


  • Heptane-1, 7-dioic acid: A 7-carbon dicarboxylic acid (pimelic acid) not used in Nylon-6,6 synthesis.
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#4 of 7 Balochistan MDCAT 2025
[Balochistan MDCAT 2025]

Which of the following is natural adhesive?
A
Silicones
B
Polyvinylacetate
C
Polyamide
D
Casein glue
View Answer & Propolis Autopsy
Correct Key: Option D Diagnostic Explanation
Concept:

Natural adhesives are bio-based polymeric substances derived directly from animal, plant, or dairy proteins and carbohydrates without synthetic polymerization.

Formula / Reaction:

Qualitative concept / No formula required.

Solution:

  • Casein glue is a natural adhesive manufactured by precipitating casein phosphoproteins from skimmed milk using dilute acid or rennet, followed by alkaline dissolution.


  • It has been used historically in woodworking, bookbinding, and label bonding.


Why other options are incorrect:

  • Silicones: Synthetic inorganic-organic polymers with a repeating \(-\text{Si}-\text{O}-\) backbone.


  • Polyvinylacetate: A synthetic thermoplastic resin prepared by the addition polymerization of vinyl acetate.


  • Polyamide: Synthetic condensation polymers containing repeating amide linkages.
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#5 of 7 Balochistan MDCAT 2025
[Balochistan MDCAT 2025]

Which of the following group acts chromophore?
A
Amino Group
B
Azo Group
C
Hydroxyl Group
D
Sulfonic Acid Group
View Answer & Propolis Autopsy
Correct Key: Option B Diagnostic Explanation
Concept:

A chromophore is an unsaturated functional group containing delocalized \(\pi\)-electrons that absorbs electromagnetic radiation in the visible region (\(400\text{--}700\text{ nm}\)), thereby imparting color to a molecule.

Formula / Reaction:

$$-\text{N}=\text{N}- \quad (\text{Azo Chromophore})$$

Solution:

  • The azo group (\(-\text{N}=\text{N}-\)) contains a double bond with a conjugated \(\pi\)-system capable of \(\pi \rightarrow \pi^*\) transitions in the visible spectrum.


  • Azo compounds constitute the largest class of synthetic organic dyes.


Why other options are incorrect:

  • Amino Group (\(-\text{NH}_2\)): An auxochrome that intensifies color and shifts absorption wavelength, but cannot impart color on its own.


  • Hydroxyl Group (\(-\text{OH}\)): An auxochrome containing lone pairs that enhance the chromophore's absorption.


  • Sulfonic Acid Group (\(-\text{SO}_3\text{H}\)): A solubilizing group used to render dye molecules water-soluble.
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#6 of 7 NUMS 2025
Polymerization of HCHO and CH3CHO occurs in the presence of:
A
DIL.H2SO4
B
Conc.H2SO4
C
Conc.H2CO3
D
DIL.H2CO3
View Answer & Propolis Autopsy
Correct Key: Option A Diagnostic Explanation
Concept:

Lower aliphatic aldehydes undergo acid-catalyzed cyclic trimerization and polymerization in the presence of dilute mineral acids.

Formula / Reaction:

$$3\,\text{HCHO} \xrightarrow{\text{Dil. }\text{H}_2\text{SO}_4} (\text{HCHO})_3 \quad (\text{Metaformaldehyde / Trioxane})$$

$$3\,\text{CH}_3\text{CHO} \xrightarrow{\text{Dil. }\text{H}_2\text{SO}_4} (\text{CH}_3\text{CHO})_3 \quad (\text{Paraldehyde})$$

Solution:

  • Dilute sulfuric acid (\(\text{dil. }\text{H}_2\text{SO}_4\)) provides the catalytic protons (\(\text{H}^+\)) required to initiate nucleophilic addition between carbonyl molecules without causing charring or dehydration.


Why other options are incorrect:

  • Conc. \(\text{H}_2\text{SO}_4\): Acts as an aggressive dehydrating and oxidizing agent, causing extensive charring, sulfonation, and oxidative decomposition.


  • Conc. \(\text{H}_2\text{CO}_3\) & Dil. \(\text{H}_2\text{CO}_3\): Carbonic acid is an unstable, weak acid that provides insufficient hydronium ion concentration to catalyze cyclic aldehyde polymerization.
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#7 of 7 Punjab MDCAT 2025
[Punjab MDCAT 2025]

Poly vinyl chloride (PVC) is the type of?
A
Homopolymer
B
Thermosetting polymer
C
Thermoplastic polymer
D
Copolymer
View Answer & Propolis Autopsy
Correct Key: Option C Diagnostic Explanation
Concept:

Thermoplastic polymers are linear or moderately branched polymers held together by intermolecular forces that soften reversibly upon heating and harden upon cooling.

Formula / Reaction:

$$-[\text{CH}_2-\text{CH}(\text{Cl})]_n- \xrightarrow{\Delta} \text{Softens (Remoldable)} \xrightarrow{\text{Cool}} \text{Hardens}$$

Solution:

  • Polyvinyl chloride (PVC) possesses linear chains with dipole-dipole attractions that can be repeatedly softened by thermal energy and reshaped.


  • Official UHS MDCAT Key Alignment: Although PVC is structurally a homopolymer, the official exam key designates Thermoplastic polymer as the correct classification based on thermal behavior.


Why other options are incorrect:

  • Thermosetting polymer: Thermosets form irreversible cross-linked covalent networks that degrade rather than melt upon heating.


  • Copolymer: Formed from two or more distinct monomer types, whereas PVC is derived entirely from vinyl chloride.


  • Homopolymer: Structurally true, but secondary to Option C in the official competitive scoring key.
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