Physical Chemistry

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Q1. What is the value of the principal quantum number (n) for an electron in the 4s orbital?

Solution:

The principal quantum number (n) indicates the energy level of the electron. For 4s, n=4.

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Q2. What is the limiting reagent when 3 moles of A react with 2 moles of B to produce 4 moles of C?

Solution:

The reaction requires 1.5 moles of B for 3 moles of A. Since only 2 moles of B are available, B is the limiting reagent.

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Q3. What is the principal quantum number for an electron in the ground state of a hydrogen atom?

Solution:

The ground state of a hydrogen atom corresponds to n=1.

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Q4. What is the freezing point depression constant (Kf) for water?

Solution:

The freezing point depression constant (Kf) for water is 1.86 °C kg/mol.

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Q5. Which of the following ions will cause the precipitation of AgCl from a solution of AgNO3?

Solution:

Cl- ions will react with Ag+ ions from AgNO3 to form AgCl, which is insoluble in water and will precipitate out.

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Q6. What is the shape of the d orbitals?

Solution:

The d orbitals have a double dumbbell shape.

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Q7. What is the pH of a 0.01 M NaOH solution?

Solution:

For NaOH, which is a strong base, pOH = -log[OH-]. [OH-] = 0.01 M, so pOH = 2. Therefore, pH = 14 - pOH = 14 - 2 = 12.

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Q8. Which of the following statements is true regarding catalysts?

Solution:

Catalysts provide an alternative pathway with a lower activation energy, thus increasing the reaction rate without being consumed.

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Q9. If 5 moles of KCl are dissolved in 1 kg of water, what is the molality of the solution?

Solution:

Molality (m) = moles of solute / kg of solvent = 5 moles / 1 kg = 5 m.

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Q10. In a reaction, if the rate constant doubles when the temperature increases by 10°C, what is the activation energy (Ea) approximately?

Solution:

Using the Arrhenius equation, Ea can be estimated to be around 40 kJ/mol.