Question

Part a please

Question 3 (30 pts) Lead nitrate (Pb(NO3)2) is a toxic compound used in lead paints in the past. It has far less use now, in specialized applications such as gold extraction. Unlike most lead salts, lead nitrate is soluble in water, as seen below in the solubility chart. After aqueous gold recovery, it is desired to recover the lead nitrate from the water via crystallization. A 70°C aqueous lead nitrate solution containing 50 wt% lead nitrate and the rest water is fed to a crystallizer operating at 10°C. Lead nitrate has a heat of solution of +31.0 kJ/mol Pb(NO3)2. This data is from Perry's (you do not need to check it) and can be used for any dilution concentration of lead nitrate in water. The reference state for this data is pure liquid water and pure solid lead nitrate at 18°C and 1 atm. The heat capacity for solid lead nitrate is 0.0087 kJ/mol C. You may assume that the heat capacities of all aqueous solutions are the same as for pure water. Show any work that you do on the diagram to determine needed information (you may draw lines in MS word or Adobe if you do not have a write-able tablet or a printer). a. Explain why lead nitrate crystallizes from solution in this process. (4 pts) 100 b. What is the production rate of crystals (kg/hr) for a feed solution of 1000 kg/hr? (10 pts) 90 80 NaNO3 70 KNO3 K2Cr2O7 60 CaCl, 50 Solubility (g of salt in 100 g H,0) Pb(NO3)2 c. At what rate must heat be removed (kJ/hr) from the crystallizer? (16 pts) KCI 40 NaCl 30 KCIO3 20 10 Ce2(SO4)3 0 10 20 30 40 50 60 70 80 90 100 From socratic.org Temperature (°C) 0

Answer 1

From the given question we see that the heat of solution is positive. This implies that when you dissolve lead nitrate in water, the result is an endothermic process

Therefore we can say that the crystallization ( which is the opposite of dissolution) would be exothermic process.

When the temperature of the solution would be lowered, the reaction would favor a exothermic process.

The primary reason for dissolution is that when the temperature is reduced all the steps involved in dissolving are overturned.

Dissolution of any molecule involves 3 major steps:

• The breaking of bonds within the solute, such as the electrostatic attraction between two ions
• The breaking of intermolecular attractive forces within the solvent, such as hydrogen bonds
• The formation of new attractive solute-solvent bonds in solution

The first 2 steps are endothermic and depend on the temperautre of the solution as temperature is an indication of the energy available. So you can see that the reduction in temperature is actually a reduction in the energy in the solvent molecules, which implies that the first 2 steps are now becoming less feasible.

Eventually crystal nuclei will be formed where the molecules that have reformed have accumulated and newly formed molecules will join these nuclei.