PHYSICAL CHEMISTRY PYQS

 10 PYQS in Physical Chemistry for Scientific assistant exam

1. Which of the following is not a crystal structure?

1. Cubic
2. Tetragonal
3. Octagonal
4. Monoclinic

Answer: Octagonal

Explanation: Seven types of crystal structures are Cubic, Tetragonal, Orthorhombic, Monoclinic, Hexagonal, Rhombohedral and Triclinic

2. Heat absorbed or released during a chemical reaction at constant pressure is called

1. Enthalpy
2. Entropy
3. Free energy
4. Internal Energy

Answer: Enthalpy

Explanation: At constant pressure the heat absorbed or released is called enthalpy (H)

                     Entropy is a measure of disorder or randomness in a system (S)

                     Internal energy is the sum of potential and kinetic energy that is the total energy of a thermodynamic system (U)

                      Free energy is the portion of the total energy that is used for converting into work under constant temperature and pressure

3. The phenomenon in which a substance absorbs light at one wavelength and emits at another wavelength is called

1. Phosphorescence
2. Fluorescence
3. Luminescence
4. All the above

Answer: All the above

Explanation: Fluorescence, phosphorescence and luminescence are phenomenon in which they absorbs light at one wavelength, gets excited and returns to lower energy state where it releases the energy higher than the incident wavelength 

4. What is the volume (in L) of 0.25 moles of CO2 gas at STP?

1. 22.4 L
2. 5.6 L
3. 0.0056 L
4. 56 L

Answer: 5.6 L

Explanation: One mole of any gas occupies 22.4 L

                      Therefore 0.25 moles occupies 0.25 * 22.4 L = 5.6 L

5. pH of 0.1 M Hcl solution is

1. 7
2. 10
3. 14
4. 1

Answer: 1

Explanation: pH = -log(H+)

                           = -log (0.1 M)

                           = 1

6. The temperature at which a vapour pressure of a liquid is equal to the atmospheric pressure is called

1. Critical temperature
2. Melting point 
3. Boiling point 
4. Sublimation point

Answer: Boiling point

Explanation: When liquid is heated its vapour pressure increases and when it reaches atmospheric pressure the vapour turns into bubbles and thus the liquid turns into gas

7. Compressibility factor of ideal gas is 

1. 0
2. 1
3. >1
4. <1

Answer: 1

Explanation: Compressibility factor (Z) describes how a real gas deviated from ideal gas

                                                          Z = PV/nRT

                      For ideal gas, PV = nRT

                      Therefore, Z = 1

                  If Z > 1, attractive forces dominate

                  If Z < 1, repulsive forces dominate

8. Which technique is most sensitive to identify CO2?

1. Infrared
2. X-ray fluorescence
3. Mass
4. UV-Visible

Answer: Infrared

Explanation: CO2 has high absorption under IR around 2349 cm-1

9. According to Graham's law

1. Rates of diffusion of gases are directly proportional to the square root of their densities  
2. Rates of diffusion of gases are inversely proportional to the square root of their densities  
3. Rates of diffusion of gases are directly proportional to their densities
4. Rates of diffusion of gases are inversely proportional to their densities

Answer: Rates of diffusion of gases are inversely proportional to the square root of their densities

10. The phenomenon in which a beam of light splits into two beams when passing through certain crystals is called

1. Refraction 
2. Diffraction
3. Birefringence
4. Polarization

Answer: Birefringence

Explanation: It is an optical property of a material that splits a single ray of beam into two different rays ordinary and extraordinary rays which is used to analyze molecular orientations

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