When heavy metals such as lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As) build up in the body they can become toxic

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 drug

After 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.

STEP1

The total volume of the mixture is Answer cm3

STEP2

The moles of Pb2+ added at the start of the reaction is Answer

The moles of drug added at the start of the reaction is Answer

STEP 3

The moles of Pb(drug)2+ at equilibrium is Answer moles

The moles of Pb2+ at equilibrium is Answer moles

The moles of drug at equilibrium is Answer moles

STEP 4

The concentration of Pb2+ at equilibrium is Answer mol dm-3

The concentration of drug at equilibrium is Answer mol dm-3

STEP 5

The 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.