1. Which of the following is used in uranium enrichment?
a) Tubular centrifuge
b) Disk-stack centrifuge
c) Gas centrifuge
d) Zippe-type centrifuge
Explanation: Gas centrifuges are used in uranium enrichment. The heavier isotope of uranium (uranium-238) in the uranium hexafluoride gas tends to concentrate at the walls of the centrifuge as it spins, while the desired uranium-235 isotope is extracted and concentrated with a scoop selectively placed inside the centrifuge. It takes many thousands of centrifugations to enrich uranium enough for use in a nuclear reactor (around 3.5% enrichment), and many thousands more to enrich it to weapons-grade (above 90% enrichment) for use in nuclear weapons.
2. What is the applied centrifugal field at a point equivalent to 5 cm from the centre of rotation and an angular velocity of 3000 rad s-1?
a) 4.5 × 10-7 cm s-2
b) 5.4 × 10-7 cm s-2
c) 3.4 × 10-7 cm s-2
d) 6.5 × 10-7 cm s-2
Explanation: The centrifugal field G, at a point 5 cm from the centre of rotation may be calculated using the equation G = ω2 r,
G = (3000)2 × 5 cm s-2 = 4.5 × 10-7 cm s-2.
3. For the pelleting of the microsomal fraction from a liver homogenate, an ultracentrifuge is operated at a speed of 40000 rpm. What is the angular velocity, ω, in radians per second?
a) 3888.8 rad s-1
b) 5680.8 rad s-1
c) 4188.8 rad s-1
d) 4288.8 rad s-1
Explanation: The angular velocity, ω, may be calculated using the equation:
ω = (2 π rev min-1)/60
ω = 2 × 3.1416 × 40000/60 rad s-1
= 4188.8 rad s-1.
4. What is rate-zonal centrifugation?
a) Based on separation of particles by mass
b) Based on separation of particles by density
c) Based on separation of particles on solubility
d) Based on separation of particles on size
Explanation: Rate-zonal centrifugation is a centrifugation technique employed to effectively separate particles of different sizes. Once the centrifugation is over, fractions are collected.
5. Which of the following is not an adsorbent?
a) Carbon
b) Polymers and resins
c) Clay
d) Dry sponge
Explanation: A sponge will absorb or take in water from another area and put it inside of itself. A dry sponge can hold more water than a wet sponge is closer to saturation and as such cannot hold more water. Sponges with more tiny holes can absorb more water than the sponges with less tiny holes and thus leads to the absorption process.
6. What do you mean by the term “Sorption”?
a) Attachment
b) Detachment
c) Diffusion
d) Thermal Expansion
Explanation: Sorption is a physical and chemical process by which one substance becomes attached to another. The reverse of sorption is desorption.
7. The desorption curve is higher than the adsorption curve.
a) True
b) False
Explanation: Theoretically, desorption curve is higher than adsorption curve in low pressure area if the material is mesoporous (2-50nm). If the material is microporous (<2nm), both curves should be matched together.
8. Which of the following isotherm is applicable to physical adsorption?
a) Langmuir
b) BET
c) Freundlich
d) Kisluik
Explanation: The Freundlich isotherm was the first isotherm model proposed for sorption processes. It can be applied for non ideal sorption on heterogeneous surfaces, as well as, multilayer sorption. A variation in the slope between 0 and 1 is associated with a chemisorption process, which is more heterogeneous as the value gets closer to 0. Due to the lack in fundamental thermodynamic basis, since there is no approach to Henry’s law at vanishing concentrations, this represents a limitation of this isotherm model.
9. Calculate the adsorption of a dye on activated carbon at 25°C, where k = 0.025, n = 0.5 and C = 0.04.
Based on the Freundlich isotherm.
a) 0.050
b) 0.030
c) 0.040
d) 0.060
Explanation: Given data
n = 0.5
Kd = 0.025
C = 0.04
Substitute the values in the corresponding equation
q = Kd C(1/n)
q = (0.025) (0.04)(1/0.5)
q = 0.040.
10. Which of the following statements regarding the physical adsorption of a gas on surface of solid is not correct?
a) On increasing temperature, adsorption increases continuously
b) Enthalpy changes are negative
c) Adsorption is specific
d) It is reversible in nature
Explanation: Physisorption is exothermic in nature. Therefore according to le chateliars principle, it occurs readily at low temperature and decreases with increase in temperature. Bond between adsorbent i.e. surface and adsorbate like gases are weak so when temperature is increasing the bond get break easily and adsorption of adsorbate get stop so rate will decrease on increasing temperature.