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.

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.

In the electrolysis of aqueous CuSO₄, Cu²⁺, SO₄²⁺, H⁺ and OH^– are the ions formed after dissociation. Copper ions have much higher reduction potential than water. Hence, these ions are easily reduced and deposited as Cu at the cathode.

Given,
N₂O₅ → 2NO₂ + 1/2 O₂
Rate = k[N₂O₅] 1
Rate = 6.25 x 10^-4 x [1.25]
Rate = 7.75 x 10^-4.

The factor e^-E_a/RT in the Arrhenius equation is called Boltzmann factor. It represents the fraction of the molecules (N_E/N_T) having energy equal to or greater than E where NE represents the number of molecules with energy E and N_T represents the total number of molecules.

Macro-molecules dissolve in a suitable solvents, gives rise to particles of colloidal size. These are normally of lyophilic type and silver solution is an example for lyophobic and multi-molecular colloids.

For an amorphous solid there is short range order present which is independent of the temperature. Long range order is present in crystalline solids.

The time taken for the zero-order reaction to complete can be calculated as follows:
When the reaction is complete, [A]₀ = 0
Therefore, k = [A]₀/t or t_100% = [A]₀/k.

Saline medium has extra salts such as sodium chloride dissolved in water. It has a greater concentration of electrolyte than ordinary medium. The ions present will favour the formation of more electrochemical cells and favour the transfer of hydrogen ions and will thus promote rusting or corrosion.

Some substances at low concentration behave as true solutions. As the concentration of the solution increases, it turns to be a colloidal solution. These type of colloids are knows as associated solution. Soaps like sodium stearate potassium stearate and detergents are examples of associated colloids whereas gum is an example for lyophilic colloids.

The electrolyte in electrolysis should contain the metal to be coated, gold in this case. AuCN is used because it is exceptionally stable and doesn’t resist the flow of Au⁺ ions from anode to cathode.

Two-dimensional close packed structure can be generated using the one-dimensional close packed structures. This can be done in 2 ways:

• By placing one row of one-dimensional structure below another in such a way that the spheres are one below the another.
• By placing one row of one-dimensional structure below another such that spheres of second row fit in the depressions of the first row.