Question #b7bcb

1 Answer
Jan 8, 2015

The answer is #7.65*10^(-3)# #"moles"# of #Pb^(2+)# ions were present in the sample.

The balanced chemical equation is:

#PbCl_(2(aq)) + Zn_((s)) -> ZnCl_(2(aq)) + Pb_((s))#

Notice the #1:1# mole ratio between #Zn# and #PbCl_2#; this means that one mole #Zn# will react with 1 mole of #PbCl_2#.

You know that #7.65*10^(-3)# moles of #Zn# had reacted after one day, which automatically means that the exact number of #PbCl_2# moles had reacted as well. The number of #PbCl_2# moles is equal to the number of moles of #Pb^(2+)# ions, since

#PbCl_(2(aq)) -> Pb_((aq))^(2+) + 2Cl_((aq))^(-)#

The complete ionic equation looks like this:

#Pb_((aq))^(2+) + 2Cl_((aq))^(-) + Zn_((s)) -> Zn_((aq))^(2+) + 2Cl_((aq))^(-) + Pb_((s))#

The net ionic equation is

#Pb_((aq))^(2+) + Zn_((s)) -> Zn_((aq))^(2+) + Pb_((s))#

This is a single replacement reaction. Since #Zn# is more reactive metal than #Pb#, the #Zn# ions will completely replace the #Pb# ions present in the solution.

http://www.bbc.co.uk/bitesize/ks3/science/chemical_material_behaviour/compounds_mixtures/revision/5/