Need help with a Past HSC question (1 Viewer)

[nomchomchikapompom]

question 23 in the 2013 past HSC paper
http://www.boardofstudies.nsw.edu.au/hsc_exams/2013/pdf_doc/2013-hsc-chemistry.pdf
answers= http://www.boardofstudies.nsw.edu.au/hsc_exams/2013/pdf_doc/2013-marking-guide-chemistry.pdf


this is what i did:

Balanced Equation:

Pb (s) + 2AgNO3 (aq) > Pb(NO3)2 (aq) + 2Ag (s)

ratio is 1:2 > 1:2

number of moles in Pb is 20.72/207.2 = 0.1000 mols

number of moles in AgNO3 = ( c= n/v) 1.00M x 0.100L= 0.100 mols

ok after this it get’s confusing … anyway ratio is 1:2 (Pb:AgNO3) so divide 0.100 mols by 2 to get Pb (why would they give you the moles anyway and why it is required to be worked out for Pb if all you need to know is the mols for AgNO3 to figure it out )

Full Ionic Equation:

Pb (s) + 2Ag+ + 2NO3-> Pb2+ + 2NO3- + 2Ag (s)

the ratio is the full ionic is 1:2:2 > 1:2:2

so that means that Pb is 0.0500 mols (0.100 divide 2) because it has a ratio of one and so all the other ions with a ration of 1 also have the same number of moles and all the ions/atoms with a ratio of 2 have 0.100 mols (but i then don't get why Ag+ has only has 0 moles if i follow the ratios)


sorry if i'm confusing, i don't even know how to ask what i need to ask lel.... oh and this is my first post on this forum so sorry if i don't use it properly or something

 

[faisalabdul16]

Silver ions are used up.

 

[HeroicPandas]

Revise limiting reagents and species in excess