12 Grades challenge/Chemistry

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Chemistry sample Q&A

Q1. Fats and oils are:

A. Acids

B. Alcohols

C. Alkenes

D. Esters

Fats and oils are esters. They are composed of fatty acids and glycerol. In these molecules, three fatty acid molecules are esterified with a glycerol molecule, resulting in the formation of triglycerides. The general structure of a fat or oil can be represented as follows:

R-COO-CH2-CHOH-CH2-COO-RR-COO-CH2-CHOH-CH2-COO-R

Here, R represents a long hydrocarbon chain that varies in length and saturation in different fats and oils. Therefore, the correct answer is D) Esters.

Q2. The reaction between alcohols and acyl chlorides produces

A. Ethers

B. Esters

C. Carboxylic acids

D. Aromatic salts

The reaction between alcohols and acyl chlorides produces esters. This reaction is known as an esterification reaction, where an alcohol and an acid chloride react to form an ester and hydrogen chloride. This reaction is a common method for the synthesis of esters. Therefore, the correct answer is B) Esters.

Q3. Which one of the following aqueous solutions will have the LOWEST freezing point?

A. Aq. 0.50m KF

B. Aq. 0.60m glucose

C. Aq. 0.24m Fel₃

D. Pure H₂O

The freezing point depression is a colligative property, meaning it depends on the concentration of solute particles, not the nature of the solute. The solution with the lowest freezing point will have the highest concentration of particles.

Let’s consider the options:

A. Aq. 0.50m KF (potassium fluoride) dissociates into K+ and F- ions. B. Aq. 0.60m glucose does not dissociate into ions. C. Aq. 0.24m FeCl3 (ferric chloride) dissociates into Fe3+ and Cl- ions. D. Pure H2O does not contain any solute particles.

Since option A contains the most ions in solution, it will have the most significant effect on lowering the freezing point compared to the other options. Therefore, Aq. 0.50m KF will have the lowest freezing point. Thus, the correct answer is A) Aq. 0.50m KF.

Q4.When a student draws a plausible Lewis structure for hydrazine molecule (N₂H₄), how many lone pair of electrons are available?

A. 1

B. 4

C. 3

D. 2

In the Lewis structure of the hydrazine molecule (N2H4), each nitrogen atom is bonded to two hydrogen atoms, and there is one lone pair of electrons on each nitrogen atom. Hence, there are a total of four lone pairs of electrons present in the Lewis structure of the hydrazine molecule. Therefore, the correct answer is B) 4.

Q5. Who used the cathode Ray tube to discover the electron and determine its charge to mass ratio?

A. Robert A. Millikan

B. James Chadwick

C. J.J Thomson

D. Ernest Rutherford

The scientist who used the cathode ray tube to discover the electron and determine its charge-to-mass ratio was J.J. Thomson. He conducted experiments with cathode ray tubes and demonstrated that cathode rays were composed of previously unknown negatively charged particles, which were later named electrons. Thomson’s work provided the first evidence for the existence of subatomic particles, and his discovery was crucial in understanding the structure of the atom. Therefore, the correct answer is C) J.J. Thomson.

Q6. Compounds that contain the carboxyl (carbonyl and hydroxyl) group are said to be:

A. Organic acids

B. Ketones

C. Aldehydes

D. Esters

Compounds that contain the carboxyl (carbonyl and hydroxyl) group are known as organic acids. The carboxyl group (-COOH) is a functional group found in organic compounds, such as carboxylic acids. It consists of a carbonyl group (C=O) and a hydroxyl group (OH) attached to the same carbon atom. This arrangement imparts acidic properties to the compound. Therefore, the correct answer is A) Organic acids.

Q7. The main ore of lead is called:

A. Zinc blend

B. Galena

C. Cinnabar

D. Chromite

The main ore of lead is called Galena. Galena is a lead sulfide mineral with the chemical formula PbS. It is the most important ore of lead and an important source of silver. Therefore, the correct answer is B) Galena.

Q8. During nitrification, bacterial convert into

A. N₂, N₂O in to nitrous oxide

B. NO₃^–, NH₄⁺ or nitrates into ammonium

C. N₂ into nitrates

D. N₂, nitrous oxide into nitrogen
During nitrification, bacteria convert ammonia (NH3) into nitrites (NO2-) and then into nitrates (NO3-). This process is a vital part of the nitrogen cycle, where certain bacteria perform the oxidation of ammonia to nitrites, and further, other bacteria oxidize the nitrites into nitrates. Therefore, the correct answer is B) NO3-, NH4+ or nitrates into ammonium.

Q9. Which one of the following metals exists in a free state?

A. Na

B. Mg

C. Pt

D. Zn

Among the options given, gold (Pt) is the only metal that can be found in its free state in nature. Gold occurs in a native state, meaning it can be found in its elemental form without combining with other elements. Therefore, the correct answer is C) Pt (Platinum).

Q10. A ___ ∆H corresponds to an ___ process.

A. Negative, endothermic

B. Positive, exothermic

C. Zero, exothermic

D. Positive, endothermic

A negative ∆H corresponds to an exothermic process. In an exothermic process, heat is released to the surroundings, resulting in a negative value for the enthalpy change (∆H). Therefore, the correct answer is A) Negative, exothermic.

Q11. Which of the following is NOT both a Bronsted-Lowry acid and a Bronsted-Lowry base?

A. HS^–

B. OH^–

C. HCO₃^–

D. HSO₄^–

A species that can act both as a Bronsted-Lowry acid and a Bronsted-Lowry base is referred to as amphiprotic. Among the options provided:

A. HS- (Hydrogen sulfide ion) can act as a Bronsted-Lowry acid by donating a proton and as a Bronsted-Lowry base by accepting a proton. B. OH- (Hydroxide ion) can act as a Bronsted-Lowry base by accepting a proton. C. HCO3- (Hydrogen carbonate ion) can act as a Bronsted-Lowry base by accepting a proton. D. HSO4- (Hydrogen sulfate ion) can act as a Bronsted-Lowry acid by donating a proton.

None of the options listed is an exception. Therefore, the correct answer is None.

Q12. Chlorine has an oxidation number of +5 in:

A. NaClO₃

B. NaClO₂

C. NaClO

D. NaClO₄

In the compounds provided, chlorine has different oxidation numbers:

A. NaClO3 (Sodium chlorate) – Chlorine has an oxidation number of +5. B. NaClO2 (Sodium chlorite) – Chlorine has an oxidation number of +3. C. NaClO (Sodium hypochlorite) – Chlorine has an oxidation number of +1. D. NaClO4 (Sodium perchlorate) – Chlorine has an oxidation number of +7.

Therefore, the compound in which chlorine has an oxidation number of +5 is A) NaClO3.

Q13. What is a measure of the closeness of a measurement to its true value?

A. Accuracy

B. Precision

C. Reproducibility

D. Usefulness

A measure of the closeness of a measurement to its true value is known as accuracy. Accuracy indicates how close a measured value is to the actual or true value of the quantity being measured. It is different from precision, which refers to the degree of agreement or reproducibility of repeated measurements. Therefore, the correct answer is A) Accuracy.

Q14. The monomer of neoprene is:

A. Butadiene

B. Isoprene

C. Chloroprene

D. 2-methyl-1,3-butadiene

The monomer of neoprene is chloroprene. Neoprene is a synthetic rubber that is produced by the polymerization of chloroprene (2-chloro-1,3-butadiene). Therefore, the correct answer is C) Chloroprene.

Q15. What is the sum of 3.72 x 10⁸ and 4.62 x 10⁷ to the correct significant figure?

A. 4.991 x 10⁷

B. 4.17 x 10⁸

C. 4.172 x 10⁸

D. 4.99 x 10⁷

To find the sum of 3.72×1083.72×108 and 4.62×1074.62×107, we need to convert one of the numbers so that they have the same exponent. Let’s convert 4.62×1074.62×107 to match the exponent of 3.72×1083.72×108 by writing it as 0.462×1080.462×108. Now, we can add the two numbers:

3.72×108+0.462×108=4.182×1083.72×108+0.462×108=4.182×108

Rounded to the correct significant figures, the sum is 4.17×1084.17×108. Therefore, the correct answer is B) 4.17×1084.17×108.

Q16. Which of the following is a natural polymer?

A. PVC

B. Rubber

C. Perspex

D. Teflon

Rubber is a natural polymer. Natural rubber is derived from the latex of certain plants, primarily the rubber tree. It is composed of repeating isoprene units, which give it its elastic properties. Therefore, the correct answer is B) Rubber.

Q17. When a sodium chromate Na₂CrO₄ solution is acidified, it is converted to:

A. Cr₂O₇^-2

B. Cr₂O₃

C. CrO₃

D. Cr(s)

Q18. Nylons are:-

A. Amides

B. Peptides

C. Polyesters

D. Polyamides

Nylons are polyamides. They are a type of synthetic polymers, often used in fibers for textiles and molded materials. These materials are known for their high durability and resilience, making them suitable for a variety of applications. Therefore, the correct answer is D) Polyamides

Q19. Which quantum number is used to be determine sub shells?

A. Principal quantum number

B. Magnetic quantum number

C. Spin quantum number

D. Azimuthal quantum number

Q20. The quantum number used to determine subshells is the Azimuthal quantum number (l). It defines the shape of the orbital and can have integral values ranging from 0 to (n-1), where n is the principal quantum number. The azimuthal quantum number helps determine the type of subshell within a principal energy level. Therefore, the correct answer is D) Azimuthal quantum number.

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Q21. The maximum kinetic energy of a photoelectron emitted from a metal is 1.03 x 10^-19J when light that has a 656 nm wavelength shines on the surface. What is the threshold frequency for this metal?

A. 4.57 x 10¹⁴s^-1

B. 3.02 x 10¹⁴s^-1

C. 3.02 x 10^-14s^-1

D. 4.57 x 10^-14s^-1

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Q22. What is the maximum number of electrons in an atom that can have the principal quantum number n = 4?

A. 34

B. 8

C. 32

D. 18

Q23. Which of the following questions expresses de Broglie’s hypothesis?

A. λ = h/(mv)

B. �∆E = hc/ λ

C. v=c/λ

D. �∆E = c/ λ

Q24. What skill is a scientist using when he/she listens to the sounds that animals make?

A. Drawing conclusions

B. Making a hypothesis

C. Interpreting data

D. Making observations

When a scientist listens to the sounds that animals make, they are engaging in the process of making observations. Observations involve gathering data or information through the senses or using tools, and this can include observing various phenomena, including animal behaviors, sounds, or other characteristics. Therefore, the correct answer is D) Making observations.

Q25. Which of the following is fundamentally different from the others?

A. Light waves

B. Radio waves

C. Sound waves

D. Microwaves

Among the options provided, sound waves are fundamentally different from the others. Sound waves are mechanical waves that require a medium, such as air, water, or solid material, to travel. On the other hand, light waves, radio waves, and microwaves are all forms of electromagnetic radiation that can travel through a vacuum.

Therefore, the correct answer is C) Sound waves.

Q26. What is (are) the bond angle (s) in SF₆?

A. 109.5⁰

B. 90⁰

C. 90⁰ and 109.5⁰

D. 180⁰

In SF6, sulfur forms six bonds with fluorine atoms, resulting in an octahedral molecular geometry. The bond angle between the six bonding pairs in an octahedral geometry is 90 degrees. Therefore, the correct answer is B) 90°.

Q27. The number of resonance structures for CO₃^-2 are:

A. 9

B. 2

C. 3

D. 6

Q28. In the following equation, what type of hybridization change, if any occurs at the Xe atom? XeF2(s) + F2(g) → XeF4(s)

A. sp³d to sp³d²

B. dsp² to sp³

C. sp³ to sp³d

D. sp³d to sp³

In the given equation, the xenon atom changes its hybridization from sp3d to sp3d2 when going from XeF2 to XeF4. This change happens because the XeF2 molecule has five electron groups around the central atom (two bonding pairs and three lone pairs), resulting in sp3d hybridization. In contrast, XeF4 has six electron groups around the central atom (four bonding pairs and two lone pairs), leading to sp3d2 hybridization.

Therefore, the correct answer is A) sp3d to sp3d2.

Q29. Which of the following compounds does NOT contain an ionic bond?

A. NaOH

B. HCl

C. K₂S

D. LiH

In the given compounds:

A. NaOH (sodium hydroxide) contains an ionic bond between sodium (Na+) and hydroxide (OH-) ions. B. HCl (hydrogen chloride) is a molecular compound with a covalent bond between hydrogen (H) and chlorine (Cl) atoms. C. K2S (potassium sulfide) contains an ionic bond between potassium (K+) and sulfide (S2-) ions. D. LiH (lithium hydride) contains an ionic bond between lithium (Li+) and hydride (H-) ions.

Among the options provided, all compounds contain at least one ionic bond. Therefore, there is no compound in the options that does NOT contain an ionic bond.

Q30. Which of the following statements about oxygen and fluorine is NOT correct?

A. O has a smaller atomic radius than F.

B. O has a smaller electron affinity than F.

C. O^2- has a larger ionic radius than F^–.

D. O and F have the same number of core electrons.

The statement “O2- has a larger ionic radius than F-” is not correct.

In general, for isoelectronic species (species with the same number of electrons), the ionic radius increases with the increase in atomic number. Since oxygen (O) and fluorine (F) are isoelectronic, their ionic radii follow the same trend. Consequently, the fluoride ion (F-) has a larger ionic radius than the oxide ion (O2-). Therefore, the correct answer is C) O2- has a larger ionic radius than F-.

Q31. What will be the charges on the ions formed when silicon reacts with nitrogen?

A. Si²⁺, N^2-

B. Si³⁺, N^3-

C. Si⁴⁺, N^2-

D. Si⁴⁺, N^3-

When silicon reacts with nitrogen, it forms a compound known as silicon nitride (Si3N4). In this compound, silicon and nitrogen ions are combined in a 1:3 ratio.

Silicon is in group 14 of the periodic table and can lose or gain four electrons to achieve a stable electron configuration. Nitrogen is in group 15 and can gain three electrons to achieve a stable electron configuration.

Therefore, the charges on the ions formed would be:

Silicon: Si^(4+)

Nitrogen: N^(3-)

The correct answer would be C. Si4+, N3-.

Q32. The equilibrium constant for the ionization of HCN is 4.9 x 10^-10
HCN ⇌ H⁺ + CN^–K = 4.9 x 10^-10
Which of the following statements is true regarding this equilibrium?
(I) The reaction is product favoured.
(II) The reaction is reactant favoured.
(III) Equilibrium lies far to the right.
(IV) Equilibrium lies far to the left.

A. II and III

B. I and IV

C. I and III

D. II and IV

The equilibrium constant (K) for the ionization of HCN is very small, at 4.9×10−104.9×10−10. A small equilibrium constant indicates that the reaction is reactant-favored and the equilibrium lies far to the left. Therefore, the correct statement is:

D. II and IV

This means that the reaction is reactant-favored, and the equilibrium lies far to the left.

33. The rate equation for the decomposition of nitramide, H₂NNO₂ → N₂O + H₂O is rate = k[H₂ NNO₂][H⁺]^-1 which of the following mechanisms is consistent with this rate equation?

A. H₂NNO₂ ⇌ H⁺ + HNNO₂     fast equilibrium
     HNNO^–₂ → N₂O + OH^–     slow
     H⁺ + OH^– → H₂O     fast

B. H₂NNO₂+ → H+ ⇌ H₃NNO⁺₂     fast
     H₃ NNO⁺₂ → N₂O + H₃O⁺     slow
     H₃O⁺ ⇌ H⁺ + H₂O     fast equilibrium

C. H₃NN⁺₂ → N₂O + H₂O slow

D. H₂NNO₂ → OH^– + NH⁺₄     slow
     NH⁺₄ ⇌ NH₃ + H⁺     fast equilibrium
     H₂O ⇌ H⁺ + OH^–     fast equilibrium

Given the rate equation, rate = k[H2 NNO2][H+]-1, it can be seen that the rate is dependent on the concentration of H2NNO2 and the inverse concentration of H+.

From the options provided, the mechanism consistent with this rate equation is:

A. H2NNO2 ⇌ H+ + HNNO2 (fast equilibrium) HNNO-2 → N2O + OH- (slow) H+ + OH- → H2O (fast)

This mechanism involves the species H2NNO2 and H+ as reactants and includes a fast equilibrium step followed by a slow step, which corresponds to the rate law provided. Therefore, the correct answer is A.

Q34. Given the equilibrium constant values:
N₂(g) + 1/2 O₂ (g) ⇌ N₂O(g) K_c = 3.4 x 10^-18
N₂O₄(g) ⇌ 2NO₂(g) K_c = 4.6 x 10^-3
1/2N₂(g) + O₂(g) ⇌ NO₂(g) K_c = 4.1 x 10^-9
What is the value of K_c for the following reaction?
2NO₂ + 3O₂(g) ⇌ 2N₂O₄(g)

A. 1.2 ?x 10^-6

B. 2.4 x 10^-6

C. 1.2 x 10⁶

D. 4.8 x 10⁶

Q35. Which of the following factors does NOT affect the rate of a chemical reaction?

A. Concentration

B. Nature of reactants

C. Temperature

D. Humidity

Q36.The factor that does NOT affect the rate of a chemical reaction is humidity. Humidity, the amount of water vapor present in the air or another gas, does not directly influence the rate of a chemical reaction. The other options – concentration, nature of reactants, and temperature – are all significant factors that can affect the rate of a chemical reaction

37. If a reaction is zero order in A, tripling the concentration of A will cause the reaction rate to:

A. Increase by a factor of 3

B. Remain constant

C. Increase by a factor of 27

D. Increase by a factor of 9

If a reaction is zero order in A, it means that the rate of the reaction is independent of the concentration of A. Therefore, any changes in the concentration of A won’t affect the rate of the reaction. In this case, tripling the concentration of A won’t change the rate of the reaction, so the correct answer is:

B. Remain constant.

Q38. The phrase “like dissolves like” refers to the fact that:

A. Polar solvents dissolve non polar solutes and vice versa

B. Solvents can only dissolve solutes of similar molar mass

C. Polar solvents dissolve polar solutes and non-polar solvents dissolve non polar solutes

D. Gases can only dissolve other gases

The phrase “like dissolves like” refers to the fact that:

C. Polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes.

Hydrolysis of an ester would produce a carboxylic acid and an alcohol. Unfortunately, I don’t have access to images or the specific structural formula you mentioned. If you provide the structural formula or more information, I can assist you further.

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