Many waste water treatment facilities have strict guidelines on the amounts of transition metals that can be discharged into the sewer systems. This creates a waste disposal problem since student experiments in general chemistry courses can generate large volumes of aqueous wastes containing high concentrations of some of these transition metals. In the CHEM 120 lab, we have generated a large amount of aqueous copper containing waste. At this point, the waste solution contains the aqueous copper species, Cu(H20)+, recall that in aqueous solution the first- row transition metals exist as the aquated ions, for simplicity we often abbreviate these as Cu?+ (ag). A cost-effective method for removing copper from aqueous solution is to precipitate the ions using a source of sulphide ion, S. By adding sodium sulphide (NazS) to the waste solution, we should be able to precipitate copper as copper sulphide and subsequently remove it by filtration: Cu? (aq) + S (aq) → CuS(aq) (The Ksp for CuS = 6.7 × 1042, this indicates a very low solubility in aqueous solution) Your task is to analyze a copper waste solution and answer the following questions: 1. How much Cut ion is present, in mol/L, in the test solution? 2. What assumptions are we making in this analysis regarding the other components present in the waste solution? 3. What mass of NazS must be added / L of solution, to precipitate the Cut ions?
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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