Question

Salt, with a density of 2000 kg/m³, is introduced at the top of a reactor filled with a 3 m depth of aqueous liquid having a density of 1000 kg/m³ and a viscosity of 0.002 Pa.s. The crystals must dissolve entirely before reaching the bottom. If the rate of dissolution of the crystals is given by a specific formula:

Which of the following statements about the dissolution process is correct?
A) Increasing the depth of the liquid will increase the dissolution rate.
B) Higher viscosity of the liquid will increase the dissolution rate.
C) A smaller interfacial area will result in a faster dissolution rate.
D) Lowering the solubility of salt in the liquid will decrease the dissolution rate.

Answer 1

The correct statement about the dissolution process is that lowering the solubility of salt in the liquid decreases the dissolution rate, because it means the salt will reach saturation more quickly and the amount of dissolved salt will no longer change.

Step-by-step explanation:

Understanding the dissolution process of salt in an aqueous liquid involves various factors that can either increase or decrease the rate at which the salt dissolves. The correct statement about the dissolution process in the student's question is D) Lowering the solubility of salt in the liquid will decrease the dissolution rate. This is because when the solubility is lower, salt crystals will dissolve slower, reaching a point of saturation more quickly where the rate of dissolution and the rate of recrystallization equalize, resulting in no net change in the dissolved amount.

Other factors that affect the dissolution rate include the surface area of the salt and the temperature of the solution; increased surface area or temperature tend to increase the rate of dissolution by enhancing solvent and solute particle interactions. However, contrary to the student's options, increasing the depth of the liquid (option A) would not affect the dissolution rate directly, higher viscosity (option B) would actually slow down the dissolution due to increased resistance to movement of molecules, and a smaller interfacial area (option C) would decrease the dissolution rate due to reduced contact between solute and solvent.