Chemistry: CUET Mock Test - 2 - CUET MCQ

Crystalline solids are composed of many small crystals, each of which is called a unit cell. It is a specific term. Monomer is the basic unit for a polymer, and atoms make up molecules, which can further arrange themselves to form solids, liquids or gases.

Kohlrausch's law states that the equivalent conductivity of an electrolyte at infinite dilution is equal to the sum of the conductances of the anions and cations. If salt is dissolved in water, the conductivity of the solution is the sum of the conductances of the anions and cations.

Given, for NaCl, HCl and NaOAc are 126.4, 425.9 and 91.0 S cm² mol^-1

= (425.9 + 91.0 – 126.4) S cm² mol^–1

= 390.5 S cm2 mol–1

For redox change

n-factor = 5

n_eq = nmol × n-factor

= 1 × 5

= 5

Charge required in Faraday = Number of n_eq

= 5 F

On electrolysis of aq. NaCl

Cathode:

Anode:

Net reaction :

Aspartame is unstable at cooking temperature therefore limited to cold foods and soft drink only.

Concept :

Artificial sweetener: as an alternative to sucrose, some artificial sweetener is used.

• The diabetic patient can’t take sucrose, but this sweetener can be taken.
• It does not take part in biochemical reactions in the body.
• And also don’t produce calories in the body.
• So these are called calorie-free sweeteners.

There are many artificial sweeteners, Major examples of artificial sweeteners are:

1. Saccharin: it is one of the popular sweeteners. the chemical name of saccharine is ortho-sulphonamide. but nowadays its uses are restricted.
2. Aspartame: it is produced from two amino acids – phenylalanine and aspartic acid. It is 200 times sweeter than sucrose. It is used in soft cold drinks.
3. Alitame: it is 2000 times sweeter than that sugar.
4. Sucralose: it is the trichloro derivative of sucrose. it is 600 times sweeter than sucrose.
5. Cyclamate and succinic acid are used as artificial sweeteners.

K = 2.3 × 10⁵ L mol^-1 s^-1

For order of reaction,

The general formula for the unit of k is mol^1-n L ^n-1 s^-1

The unit of rate constant

The unit ‘L mol^–1 s^–1 ’ corresponds to the 2nd-order reaction.

Correct answer: 2)

Concept:

• A catalyst is any material in chemistry that increases the rate of a reaction without being ingested.
• A small amount of the catalyst can catalyse a large amount of reactants.
• A catalyst does not alter Gibbs energy of a reaction.
• It catalyses the spontaneous reactions but does not catalyse non-spontaneous reactions.
• A catalyst does not change the equilibrium constant of a reaction rather, it helps in attaining the equilibrium faster.
• A catalyst is a material that speeds up or slows down the rate of a chemical reaction.
• The rate of reaction is accelerated by a positive catalyst.
• The rate of reaction is slowed by a negative catalyst.
• Catalyst has no effect on the number of products produced.
• Enzymes are bio-catalyst, which are temperature and pH sensitive, they lose their function when the pH or temperature increases or decreases.

Explanation:

• A catalyst is a substance which alters the rate of a reaction without itself undergoing any permanent chemical change.
• According to intermediate complex theory, reactants first combine with catalyst to form intermediate complex which then decomposes to form the products and regenerating the catalyst.

• Catalyst provides an alternate pathway by reducing the activation energy between reactants and products and hence lowering the potential energy barrier.
• Enzymes are the biological catalyst which are temperature and pH sensitive, they lose their function when the pH or temperature increases or decreases.

Conclusion:
Thus, the statement, catalysts do not get the involved process of reaction is incorrect.

Correct answer: 4)
Concept:

• A catalyst is any material in chemistry that increases the rate of a reaction without being ingested.
• A small amount of the catalyst can catalyse a large amount of reactants.
• A catalyst does not alter Gibbs energy of a reaction.
• It catalyses the spontaneous reactions but does not catalyse non-spontaneous reactions.
• A catalyst does not change the equilibrium constant of a reaction rather, it helps in attaining the equilibrium faster.
• A catalyst is a material that speeds up or slows down the rate of a chemical reaction.
• The rate of reaction is accelerated by a positive catalyst.
• The rate of reaction is slowed by a negative catalyst.
• Catalyst has no effect on the number of products produced.
• Enzymes are bio-catalyst, which are temperature and pH sensitive, they lose their function when the pH or temperature increases or decreases.

Explanation:

• A catalyst is a substance that speeds up of a chemical reaction, or lowers the temperature or pressure needed to start the reaction, without itself being consumed during the reaction.
• Catalysis is the process of adding a catalyst to facilitate a reaction.
• The presence of a catalyst increases the reaction rate (in both forward and reverse reactions) by providing an alternative pathway with lower activation energy.
• If the activation energy is lowered, more reactants can cross that barrier easily so, the rate of effective collision also increased and so, the rate of reaction increases.
• Photocatalyst absorb the energy of different wavelength and provide them to reactants in the desired wavelength.
• A catalyst can lower the activation energy for a reaction by: orienting the reacting particles in such a way that successful collisions are more likely.
• Catalyst reacting with the reactants to form an intermediate that requires lower energy to form the product.

Conclusion:
Thus, all the given options are correct.

Correct answer: 1)
Concept:

• A catalyst is any material in chemistry that increases the rate of a reaction without being ingested.
• A small amount of the catalyst can catalyse a large amount of reactants.
• A catalyst does not alter Gibbs energy of a reaction.
• It catalyses the spontaneous reactions but does not catalyse non-spontaneous reactions.
• A catalyst does not change the equilibrium constant of a reaction rather, it helps in attaining the equilibrium faster.
• A catalyst is a material that speeds up or slows down the rate of a chemical reaction.
• The rate of reaction is accelerated by a positive catalyst.
• The rate of reaction is slowed by a negative catalyst.
• Catalyst has no effect on the number of products produced.
• Enzymes are bio-catalyst, which are temperature and pH sensitive, they lose their function when the pH or temperature increases or decreases.

Explanation:

• Conversion of vanaspati oil to vanaspati ghee is known as Hydrogenation.
• Vegetable oils are unsaturated compounds.
• On heating of vegetable oils in the presence of nickel catalyst converts the unsaturated fat to saturated fats called vegetable ghee also known as vanaspati ghee.
• This process is known the hydrogenation of vegetable oils.

• In this process, oils are adsorbed on the surface of the catalyst along with some of the hydrogen.
• Hydrogens shift from the metal surface to the carbons of the double bonds present in the oils and the resulting saturated hydrocarbon which is more weakly adsorbed, leaves the catalyst surface.
• The nickel catalyst is then removed from the hydrogenated fat by the process of filtration.

Conclusion:

Thus, raney nickel is used in the hydrogenation of Vanaspati oil.

Correct answer: 3)
Concept:

• A catalyst is any material in chemistry that increases the rate of a reaction without being ingested.
• A small amount of the catalyst can catalyse a large amount of reactants.
• It catalyses the spontaneous reactions but does not catalyse non-spontaneous reactions.
• A catalyst does not change the equilibrium constant of a reaction rather, it helps in attaining the equilibrium faster.
• A catalyst is a material that speeds up or slows down the rate of a chemical reaction.
• The rate of reaction is accelerated by a positive catalyst.
• The rate of reaction is slowed by a negative catalyst.
• When the reactants and the catalyst are in the same phase (i.e. solid, liquid or gas). The catalysis is said to be homogeneous
• Enzymes are bio-catalyst, which are temperature and pH sensitive, they lose their function when the pH or temperature increases or decreases.

Explanation:

• Catalyst is a substance which speeds up and speeds down a chemical reaction without itself being used up at the end of the reaction and the phenomenon is known as catalysis.
• The catalytic process in which the reactants and the catalyst are in different phases is known as heterogeneous catalysis.
• Catalytic poisons : Substances which destroy the activity of the catalyst by their presence are known as catalytic poisons.
• The catalyst provides a new pathway involving lower amount of activation energy.
• Selectivity is the ability of catalysts to direct a reaction to yield particular products (excluding other).
• A particular catalyst catalyses only one kind of reaction.

Conclusion:

Thus, only option 3 is correct regarding catalyst.

Correct answer: 2)
Concept:

• Enzymes are complex nitrogenous substances secreted by low forms of vegetables & organisms.
• Enzymes are actually protein molecules of higher molecular mass.
• Enzymes form colloidal solutions in water and are very effective catalysts.
• They catalyse numerous reactions, especially those connected with natural processes.
• Numerous reactions occur in the bodies of animals and plants to maintain the life process.
• These reactions are catalysed by enzymes.
• The enzymes are thus, termed as bio-chemical catalysts and the phenomenon is known as bio-chemical catalysis.

Explanation:

• Enzymes works or catalyse a biochemical reaction by lowering the activation energy barrier of the reaction.
• Enzymes are temperature sensitive, they tend to denature in high temperatures, the optimal temperature for the enzymes in the human body is around 37 degrees celsius.
• pH plays an important role in enzyme activity, enzymes are often active only in a narrow pH range. So they are pH sensitive.
• Each enzyme typically binds only one substrate. Enzymes are not consumed during a reaction; instead they are available to bind new substrates and catalyze the same reaction repeatedly.
• Enzymes are usually highly selective, catalysing specific reactions only. This specificity is due to the shapes of the enzyme molecules.
• Some enzymes have multi-site, are known as multi-site enzymes, defined as where multiple substrate molecules can bind simultaneously to the same enzyme molecule, play a key role in a number of biological networks.

Conclusion:
Thus, an enzyme can also accommodate numerous substrate molecules simultaneously is only the correct option.

Given,
K = 0.01s^-1
t_1/2 = 0.693/0.01
t_1/2 = 69.3s
[R] = [R]₀/2ⁿ
2ⁿ = [R]₀/[R]
2ⁿ = 2.4/0.3
2ⁿ = 8
n = 3 (number of half-lives)
For 1 half-life t_1/2 = 69.3s
For 3 half-life 3t_1/2 = 3 x 69.3s = 207.9s.

There are two polymorphous structures of sulfur, rhombic and monoclinic. Polymorphous structures occur when a single substance can crystallize in two or more forms depending upon the conditions.

Isomorphous is when two or more substances have the same crystal structure. Polymorphous is when a single substance can crystallize in two or more forms depending upon the conditions.

Aqua regia also known as royal water is a yellow-orange mixture of concentrated nitric acid and hydrochloric acid in the ratio 1:3. It is used by an alchemist to dissolve noble metals like gold and silver.

Given,
K = 7.5 x 10^-3 s^-1
K = (2.303/t) x log([R]₀/[R])
t = (2.303/7.5 x 10^-3) x log([100]/[25])
t = (2.303/7.5 x 10^-3) x 0.6
t = 38.4s.

The effect of temperature on the rate of a reaction is usually expressed in terms of the temperature coefficient which is defined by the equation:
Temperature coefficient (n) = Rate constant at T + 10° (308 K)/Rate constant at T° (298 K).

Starch solution, gelatin and gum are colloids in which the dispersed phase has very high affinity for the dispersion medium and therefore they are categorized as lyophilic colloids. Silver solution on the other hand is an example of lyophobic colloids.

Electrodes which do not take part in the chemical reaction during electrolysis are known as inert electrodes. Gold, silver and graphite do not take part in the process, but graphite is preferred because gold and silver electrodes are expensive.

t_25% = (1-0.75)/K
K = 0.25/30
t_50% = (1 x 30)/(2 x 0.25)
t_50% = 15/0.25
t_50% = 60s.

The density of ice is about 0.92 g/cm³ while that of water is 1 g/cm³. Mercury has density 14.184 g/cm³ as solid and 13.69 g/cm³ as liquid. Carbon dioxide has density 1.56 g/cm³ as solid and 1.10 g/cm³ as liquid. NaCl has density 2.71 g/cm³ as solid and 1.556 g/cm³ in molten state. Therefore only ice has lesser density as a solid than as a liquid.

Gold solution, Sulphur solution and blood are colloids in which the dispersed phase has very low affinity for the dispersion medium and once the dispersed phase and dispersion medium are separated we cannot get the solution directly by remixing the two phases. Therefore they are categorized under lyophobic colloids.

In the electrolysis of NaCl, if the electrolyte is molten NaCl, then the only ions formed after dissociation are Na⁺ and Cl^– ions. The cathode being a negatively charged electrode attracts the positive Na⁺ ions and neutralizes it to form Sodium metal.

A reaction is said to be of the first order if the rate of the reaction depends upon one concentration term only. The integrated rate equation for a first order reaction in exponential form is [A] = [A]₀e^-kt.

With the increase of temperature, the peak shifts forward but downward. This is because with the increase of temperature, the most probable kinetic energy increases and the fraction of molecules possessing most probable kinetic energy decreases.

In solids, the constituent particles tend to be closely packed due to strong forces between them. Hence, solids are stable and have a definite shape.

Na₂SO₄ dissociates into Na⁺ and SO₄^2- ions in the electrolysis of aqueous Na₂SO₄. Na⁺ has much lower reduction potential than water and hence Na⁺ ions are not reduced at the cathode. Instead, reduction of water occurs giving out hydrogen gas at the cathode.

Arrhenius factor(A) = 4 x 10¹³ collisions/sec
Activation energy (E_a)=98.6KJ/mol=98.6 x 10³J/mol, T=303 K
log K = log A – (E_a/2.303RT)
log K = log (4 x 10¹³) – (98.6 x 10³)/(2.303 x 8.314 x 303)
log K = 13.6020 – (98.6 x 10³/5801.584)
log k = -3.39
K = 10^-3.39
K = 4.07 x 10^-4.

Quantitatively, the effect of temperature on the rate of a reaction and hence on the rate constant k, was proposed by Arrhenius in 1889. The equation, called Arrhenius equation, is usually written in the form k = A e^-E_a/RT.

In this type of colloidal solution, a large number of atoms or small molecules aggregate to form a particle of colloidal size, these are normally of lyophobic type. Starch solution is an example of lyophilic colloids and hence is not an example for multi-molecular colloids.