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Kpk Chemistry 2018 — Solved Past Paper with Answers
All 18 MCQs from Kpk Chemistry 2018, solved with the correct answer highlighted and a full explanation for every question. This is a free MDCAT KPK / ETEA past paper — no signup, no ads. Practise it interactively in timed mode, drill more with free MDCAT MCQs, or browse all KPK / ETEA papers.
Attempt this paper interactively →Q1. The reduction of C=O to CH2 is carried out with.......?
- A. Catalytic reduction
- B. Zn-Hg and cons.HCI
- C. Wolf-Kishner Reduction✓
- D. LiAIH4
Explanation: Process: Involves hydrazine (NH₂NH₂) and a strong base (KOH), followed by heating.Outcome: Reduces carbonyl groups (C=O) to methylene groups (CH₂).Conclusion: Specifically correct for reducing C=O to CH₂.
Why the other options are wrong
- A. Process: Uses hydrogen gas and a metal catalyst (like Pd/C).Outcome: Reduces carbonyl groups to alcohols (R-CHO to R-CH₂OH).Conclusion: Does not reduce C=O to CH₂.
- B. Process: Uses zinc amalgam in concentrated hydrochloric acid.Outcome: Reduces carbonyl groups to methylene groups (R-CO-R to R-CH₂-R).
- D. Process: Uses lithium aluminium hydride.Outcome: Reduces carbonyl groups to alcohols (R-CHO to R-CH₂OH).Conclusion: Does not reduce C=O to CH₂.
Q2. Which is the strongest acid?
- A. Ethanol
- B. Acetic acid
- C. Chloroacetic acid
- D. Flouroacetic acid✓
Explanation: Flouroacetic acid ,with the structure FCH₂COOH, is the strongest acid among the given options. When it donates a proton, it forms the fluoroacetate ion (FCH₂COO⁻). The fluorine atom is highly electronegative and exerts a very strong inductive electron-withdrawing effect. This effect greatly stabilizes the conjugate base by pulling electron density away, making the fluoroacetate ion extremely stable. Because the conjugate base is highly stabilized, fluoroacetic acid readily donates a proton, making it the strongest acid.
Why the other options are wrong
- A. Ethanol is a very weak acid. Its structure is CH₃CH₂OH. When ethanol donates a proton, it forms the conjugate base known as the ethoxide ion (CH₃CH₂O⁻). This ion is not stabilized by resonance or any significant inductive effects. Because the ethoxide ion is not stabilized, ethanol does not easily donate a proton, making it the weakest acid among the given options.
- B. Acetic acid, with the structure CH₃COOH, is a weak acid. When it donates a proton, it forms the acetate ion (CH₃COO⁻) as its conjugate base. The acetate ion is stabilized by resonance, which means the negative charge is delocalized over two oxygen atoms. This resonance stabilization makes acetic acid a stronger acid compared to ethanol. However, it is still weaker than chloroacetic acid and fluoroacetic acid due to the absence of additional electron-withdrawing effects.
- C. Chloroacetic acid has the structure ClCH₂COOH. It is stronger than acetic acid because of the presence of the electronegative chlorine atom. When chloroacetic acid donates a proton, it forms the chloroacetate ion (ClCH₂COO⁻). The chlorine atom exerts an inductive electron-withdrawing effect, pulling electron density away from the conjugate base and further stabilizing it. This increased stabilization of the conjugate base makes chloroacetic acid a stronger acid than acetic acid.
Q3. ............is/are polynucleotide molecule/molecules.?
- A. DNA
- B. RNA
- C. Both DNA and RNA✓
- D. Carbohydrate
Explanation: Both DNA and RNA are correct as polynucleotide molecules. DNA carries genetic information and is found in the nucleus of cells, while RNA is involved in translating this information into proteins and is found both in the nucleus and the cytoplasm of cells.
Why the other options are wrong
- A. DNA is a polynucleotide molecule composed of long chains of nucleotides containing a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases. These bases are adenine (A), thymine (T), cytosine (C), and guanine (G). The structure of DNA forms a double helix, with two strands running in opposite directions and held together by hydrogen bonds between complementary base pairs (A-T and C-G).
- B. RNA is also a polynucleotide molecule, similar to DNA but with a few key differences. RNA contains ribose sugar instead of deoxyribose and uracil (U) instead of thymine (T) as one of the nitrogenous bases. RNA plays various roles in protein synthesis and gene regulation, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
- D. Carbohydrate is incorrect. Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They serve as a source of energy and structural components in living organisms but are not polynucleotide molecules like DNA and RNA.
Q4. Mauve is an example...dye?
- A. Acidic
- B. Basic✓
- C. Direct
- D. Azo
Explanation: Basic dyes are positively charged and are attracted to negatively charged components, such as nucleic acids and some proteins, in cells and tissues. Mauve is a basic dye, making this option correct.
Why the other options are wrong
- A. Acidic dyes are negatively charged and are commonly used to stain basic, or positively charged, components of cells and tissues. Mauve is not an acidic dye; it is a basic dye.
- C. Direct dyes are a class of dyes that are applied directly to the substrate without the need for a mordant. Mauve is not a direct dye; it is a basic dye.
- D. Azo dyes contain one or more azo (-N=N-) chromophores. These dyes can be acidic, basic, or neutral depending on their chemical structure. Mauve is not specifically an azo dye; it is a basic dye.
Q5. Pollutants have adverse effet over........?
- A. Biosphere
- B. Ecosystem
- C. Hydrosphere
- D. All of these✓
Explanation: Option D is correct because pollutants can have adverse effects on the biosphere, ecosystems, and the hydrosphere. Pollution is a global issue that impacts various aspects of the environment, ecosystems, and human health.
Why the other options are wrong
- A. The biosphere is the global sum of all ecosystems and includes all living organisms. Pollutants can have adverse effects on the biosphere by contaminating food chains, harming organisms, and disrupting ecosystems.
- B. An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. Pollutants can disrupt ecosystems by affecting the balance of species, altering habitats, and reducing biodiversity.
- C. The hydrosphere is all the waters on the Earth's surface, such as lakes, rivers, seas, and oceans. Pollutants can contaminate water bodies, leading to water pollution, which has adverse effects on aquatic life and human health.
Q6. How many types of "NMR" protons are there in butanoic acids?
- A. 8
- B. 2
- C. 6
- D. 4✓
Explanation: Option D is correct. Butanoic acid has four types of protons. One type is from the methyl group (-CH₃), and the other three types are from the three different methylene groups (-CH₂-) in the carbon chain. Each of these groups gives rise to a distinct NMR signal due to its unique chemical environment.
Why the other options are wrong
- A. This is incorrect. Butanoic acid contains four carbon atoms, so there are four unique types of protons corresponding to each carbon atom in the molecule. Each carbon atom in the chain is bonded to different numbers and types of hydrogen atoms, leading to four distinct environments for the protons.
- B. This is incorrect. While butanoic acid has two types of carbon atoms in terms of their bonding environment (methyl and methylene carbons), each type of carbon atom is bonded to different numbers and types of hydrogen atoms, resulting in four types of protons.
- C. This is incorrect. Butanoic acid has four types of protons, not six. The protons in the methyl group (-CH₃) are different from those in the methylene group (-CH₂-) adjacent to the carboxyl group (-COOH), and these are different from the protons in the methylene groups further away in the carbon chain.
Q7. Malachite is an ore of......?
- A. Mn
- B. Fe
- C. Cu✓
- D. Cr
Explanation: Cu stands for copper. Malachite is indeed an ore of copper. It is a secondary mineral formed from the weathering of copper ores, typically containing high levels of copper carbonate hydroxide.
Why the other options are wrong
- A. Mn stands for manganese. Malachite is not an ore of manganese; it is primarily composed of copper carbonate.
- B. Fe stands for iron. Malachite is not an iron ore; it does not contain significant amounts of iron.
- D. Cr stands for chromium. Malachite is not an ore of chromium; it does not contain significant amounts of chromium.
Q8. The detection of which element is an organic compound does not make use of Lassaigne's solution?
- A. Nitrogen
- B. Sulphur
- C. Halogens
- D. Carbon✓
Explanation: Lassaigne's test does not detect carbon in an organic compound. Carbon is a ubiquitous element in organic compounds and is not specifically tested for using Lassaigne's solution. Other methods, such as combustion analysis, are used to determine the carbon content of organic compounds.
Why the other options are wrong
- A. Lassaigne's test is used to detect the presence of nitrogen in an organic compound. In this test, the organic compound is heated with sodium metal and then boiled with water. The resulting solution (Lassaigne's extract) is treated with iron(II) sulfate, and a blue or purple color indicates the presence of nitrogen.
- B. Lassaigne's test can also be used to detect the presence of sulfur in an organic compound. When the Lassaigne's extract is treated with lead acetate, a black precipitate of lead sulfide is formed, indicating the presence of sulfur.
- C. Lassaigne's test can be used to detect the presence of halogens (chlorine, bromine, iodine) in an organic compound. When the Lassaigne's extract is treated with silver nitrate, a precipitate of silver halide is formed, which can help identify the halogen present.
Q9. Which one of the given deactivates benzenening and o/P- directing?
- A. -NH2
- B. -OH
- C. -OCH3
- D. -CI✓
Explanation: The chlorine atom (-Cl) is a meta director and deactivates the benzene ring. It directs substitution to the meta position relative to itself. The presence of a halogen like chlorine, especially in a meta position, deactivates the ring due to its strong electron-withdrawing nature.
Why the other options are wrong
- A. The amino group (-NH₂) is an ortho/para director, meaning it directs substitution to the ortho and para positions. However, it is an activating group, meaning it increases the rate of electrophilic aromatic substitution reactions. It does not deactivate the benzene ring.
- B. The hydroxyl group (-OH) is also an ortho/para director and activates the benzene ring. It does not deactivate the ring.
- C. The methoxy group (-OCH₃) is an ortho/para director and activates the benzene ring. It does not deactivate the ring.
Q10. Nitrobenzene reacts with chlorine in presence of AlCl3 the product obtained is......?
- A. o-Chloro Nitrobenzene
- B. m-Chloro Nitrobenzene✓
- C. p-Chloro Nitrobenzene
- D. All of these
Explanation: m-Chloro Nitrobenzene is the major product obtained when nitrobenzene reacts with chlorine in the presence of AlCl3. The chlorine atom substitutes at the meta position relative to the nitro group.
Why the other options are wrong
- A. Nitrobenzene reacts with chlorine in the presence of AlCl3 to give predominantly m-chloro nitrobenzene. The ortho position is deactivated due to the presence of the nitro group, making it less favorable for electrophilic substitution.
- C. The para position is also less favorable due to steric hindrance from the nitro group. As a result, the para-chloro product is obtained in smaller amounts compared to the meta product.
- D. While all three isomers can be formed to some extent, the major product obtained is m-chloro nitrobenzene due to the deactivating nature of the nitro group.
Q11. Which one of the given haldes is the most reactive towards nucleophlic subsolution reaction?
- A. C2H5Br
- B. C2H5l✓
- C. C2H5F
- D. C2H5Cl
Explanation: Ethyl iodide is the most reactive towards nucleophilic substitution reactions among the options. Iodine is more polarizable than bromine and chlorine, making the C2H5I bond more susceptible to nucleophilic attack.
Why the other options are wrong
- A. Ethyl bromide is less reactive than ethyl iodide towards nucleophilic substitution reactions. Bromine is less polarizable than iodine, making the C2H5Br bond less susceptible to nucleophilic attack.
- C. Ethyl fluoride is less reactive than ethyl chloride towards nucleophilic substitution reactions. Fluorine is highly electronegative, making the C2H5F bond less susceptible to nucleophilic attack.
- D. Ethyl chloride is less reactive than ethyl iodide towards nucleophilic substitution reactions. Chlorine is less polarizable than iodine, making the C2H5Cl bond less susceptible to nucleophilic attack.
Q12. The reaction of alcohol with sodium products.....?
- A. Ethane
- B. Ethene
- C. Alkoxide✓
- D. Aldehyde
Explanation: When an alcohol reacts with metallic sodium, it forms an alkoxide. This reaction involves the deprotonation of the alcohol by sodium to form the alkoxide and hydrogen gas.
Why the other options are wrong
- A. Ethane is a hydrocarbon and is not typically produced in the reaction of an alcohol with sodium.
- B. Ethene is also a hydrocarbon and is not typically produced in the reaction of an alcohol with sodium.
- D. The reaction of an alcohol with sodium does not typically produce an aldehyde. Aldehydes are usually formed from the oxidation of primary alcohols, not from their reaction with sodium.
Q13. The solubility of Mg(OH)2......By the addition of NH4CI ?
- A. Increases✓
- B. Decreases
- C. May increase or decrease
- D. Remain same
Explanation: The addition of NH4Cl to Mg(OH)2 actually increases its solubility. This is due to the common ion effect. NH4Cl dissociates in water to form NH4+ and Cl- ions. The NH4+ ions react with the OH- ions from Mg(OH)2 to form NH3 and H2O. This reaction reduces the concentration of OH- ions, which shifts the equilibrium of Mg(OH)2 dissolution to the right, increasing its solubility.
Why the other options are wrong
- B. This is the opposite of what happens. As explained above, the addition of NH4Cl increases the solubility of Mg(OH)2.
- C. The solubility of Mg(OH)2 actually increases when NH4Cl is added, so this option is incorrect.
- D. The solubility of Mg(OH)2 does not remain the same when NH4Cl is added. It increases due to the common ion effect.
Q14. Which one of the given has the maximun electronegativity?
- A. Li
- B. Na
- C. K
- D. Cs✓
Explanation: Cesium (Cs) has the maximum electronegativity among the given options. It is the most electronegative alkali metal and the least metallic in character among them.
Why the other options are wrong
- A. Lithium (Li) has a relatively low electronegativity compared to the other options. It is the least electronegative among the alkali metals listed.
- B. Sodium (Na) has a higher electronegativity than lithium but is still lower than potassium and cesium.
- C. Potassium (K) has a higher electronegativity than both lithium and sodium but is lower than cesium.
Q15. Dolomite is the mineral of...?
- A. Be
- B. Ca✓
- C. Mg
- D. K
Explanation: Dolomite is primarily composed of calcium carbonate and magnesium carbonate. It is a mineral of calcium (Ca) and magnesium (Mg), but calcium is the dominant element in dolomite.
Why the other options are wrong
- A. Dolomite is not a mineral of beryllium (Be). Beryllium is a different element and forms its own minerals, such as beryl.
- C. While dolomite does contain magnesium carbonate, calcium is the more dominant element in dolomite. Therefore, it is not considered the primary mineral of magnesium (Mg).
- D. Dolomite is not a mineral of potassium (K). Potassium forms its own minerals, such as potassium feldspar.
Q16. Which one of the given gives peroxide when heated with oxygen?
- A. Be
- B. Ca✓
- C. K
- D. Mg
Explanation: Calcium (Ca) can form calcium peroxide (CaO2) when heated with oxygen. This reaction occurs when calcium reacts with oxygen in the presence of excess oxygen or at high temperatures, forming the peroxide compound.
Why the other options are wrong
- A. Beryllium (Be) does not readily form peroxides when heated with oxygen. It is less reactive than calcium and does not exhibit this behavior.
- C. Potassium (K) can form peroxides, but it is less common compared to calcium. Potassium peroxide (K2O2) can be formed under specific conditions, but it is not as readily formed as calcium peroxide.
- D. Magnesium (Mg) does not readily form peroxides when heated with oxygen. It is less reactive than calcium and does not exhibit this behavior under normal conditions.
Q17. Oxidation state is defined as the apparent Charge...... on an atom of an element in a molecule or ion?
- A. Positive
- B. Negative
- C. Positive or negative✓
- D. None of these
Explanation: Oxidation states can be positive, negative, or even zero, depending on the number of electrons gained or lost by an atom.
Why the other options are wrong
- A. While oxidation states can be positive, they can also be negative or zero. The oxidation state is a measure of the apparent charge on an atom, but it is not always positive.
- B. Oxidation states can indeed be negative, especially in cases where an atom gains electrons. Negative oxidation states indicate that the atom has gained electrons and has a negative charge.
- D. This option is incorrect because oxidation states are defined as the apparent charge on an atom, which can be positive, negative, or zero.
Q18. Which one of the given is acidic in nature?
- A. Al2O3
- B. CO2✓
- C. CO
- D. CaO
Explanation: Carbon dioxide (CO2) is acidic in nature. When dissolved in water, it forms carbonic acid (H2CO3), which is a weak acid. This acid formation is why carbon dioxide is a major contributor to acid rain.
Why the other options are wrong
- A. Aluminum oxide (Al2O3) is an amphoteric oxide, meaning it can act as both an acid and a base. In its reaction with bases, it behaves as an acid, and in its reaction with acids, it behaves as a base. However, it is not primarily considered acidic in nature.
- C. Carbon monoxide (CO) is not acidic in nature. It is a neutral oxide and does not exhibit acidic properties.
- D. Calcium oxide (CaO), also known as quicklime, is a basic oxide. It reacts with water to form calcium hydroxide, which is a strong base. It is not acidic in nature.
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