When heavy metals such as lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As) build up in the body they can become toxic. Chelation therapy is a useful tool to treat heavy metal poisoning. In this medical procedure special drugs that can act as ligands are used to bind strongly to these metal ions. The resulting metal-drug complexes are readily excreted from the body thus lowering heavy metal concentration to safe levels. A measure of how effectively these drugs will bind to and remove heavy metal ions is the equilibrium constant, K.Company ABC Ltd. has developed a potential new compound for chelation therapy. It reacts with Pb as shown in the equation below.Pb2+ + drug Pb(drug)2+ Solutions of Pb2+ and the new drug were mixed and allowed to react until equilibrium was attained. The following solutions were mixed:100 cm3 of 1.00 x 10-3 mol dm-3 Pb2+100 cm3 of 2.00 x 10-3 mol dm-3 drugAfter equilibrium was attained, the mixture had a concentration of 1.00 x 10-4 mol dm-3 of the Pb(drug)2+ complex.Use the information provided and follow the steps below to determine the equilibrium constant, K, for the reaction.STEP1The total volume of the mixture is Answer cm3STEP2The moles of Pb2+ added at the start of the reaction is AnswerThe moles of drug added at the start of the reaction is AnswerSTEP 3The moles of Pb(drug)2+ at equilibrium is Answer molesThe moles of Pb2+ at equilibrium is Answer molesThe moles of drug at equilibrium is Answer molesSTEP 4The concentration of Pb2+ at equilibrium is Answer mol dm-3The concentration of drug at equilibrium is Answer mol dm-3STEP 5The equilibrium constant is_K=[Pb(drug)2+]=Answer[Pb2+] [drug]The Answer the K value the more effectively a chelation drug will perform. Therefore this new compound is Answer effective than the existing treatment which has a K of 1 x 108.
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