anonymous
  • anonymous
"What mass of PbCl2 contains 1.0X10^24 atoms Cl?"
Chemistry
  • Stacey Warren - Expert brainly.com
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SOLVED
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jamiebookeater
  • jamiebookeater
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aaronq
  • aaronq
first, find the mass percent compositions of Cl in PbCl. then find how many grams 1.0*10^24 atoms of Cl equate to. the rest should be straight forward
aaronq
  • aaronq
composition* not plural
anonymous
  • anonymous
Huh? I am sorry, but I am still confused. I know the answer should be 230g. Mass Percent of Cl in PbCl2= 26%? What do I do?

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aaronq
  • aaronq
whats the mass of that many Cl atoms?
anonymous
  • anonymous
71
anonymous
  • anonymous
or i am not sure :(
aaronq
  • aaronq
\(n=\dfrac{N}{N_A}=\dfrac{1.0*10^{24}}{6.023*10^{23}}\)=1.66 moles N= number of atoms (or molecules), \(N_A\) = avogadros number \(m_{Cl}=n_{Cl}*M_{Cl}\)=1.66 moles*35.45g/mol=58.847 g
aaronq
  • aaronq
good so far?
anonymous
  • anonymous
somewhat yes
anonymous
  • anonymous
how to go from that to eventually 230g?
anonymous
  • anonymous
and what does m stand for in the second equation
aaronq
  • aaronq
m = mass (in g), M=molar mass
aaronq
  • aaronq
so, 26%*m=58.847 g m=58.847g/0.26=226.3346153846153846
aaronq
  • aaronq
i didn't round, so my answer is a bit off from what you expected (230 g)
anonymous
  • anonymous
thanks, i'm going to try to write it out on paper to see if i understand :). Ill be right back
aaronq
  • aaronq
okay !
anonymous
  • anonymous
so I haven't learned those two equations (in the first part), where did you get them from and when are we supposed to use it?
anonymous
  • anonymous
and the 1.66 moles is moles of Cl? and not PbCl2?
aaronq
  • aaronq
these equations? \(n=\dfrac{N}{N_A};\;\; m=n*M\)
aaronq
  • aaronq
yeah 1.66 moles of Cl because you're using the amount of atoms of Cl not the whole molecule
anonymous
  • anonymous
ya! those equations. My teacher hasn't showed us that yet. and why did you calcualte 26% (mass percent) + why did divide w/ the mass percent? Also, why didn't we use the molar mass of PbCl2 and just stayed w/ mass of Cl2 the whole time? thanks!
aaronq
  • aaronq
we'll the first one isn't really an equation, it's just using the definition of a mole. 1 mole = 6.023*10^23 atoms, so it's merely a conversion. They should be in your book, it's one of the first concepts you see in stoichiometry. the 2nd is just a rearrangement of \(n=\dfrac{m}{M}\), also seen early in stoichiometry. We only used molar mass of Cl because were asked about Cl atoms not PbCl2 molecules. We used the mass percent because we needed to lol. for example, i tell you that 50% by mass of my backpack is books and i tell you that i have 10 books (atoms) each weighing (1 g). Whats the total mass of my backpack? 10 books = 10g 10g=50% of the backpack so to find the mass of the backpack 10g=\(m_{backpack}\)50% \(\rightarrow m_{backpack}=\dfrac{10g}{50\%}\ \) 50%=0.5 \(m_{backpack}=\dfrac{10g}{0.5}\)
anonymous
  • anonymous
simple! use unitary (ratio method) i.e: if (6.02x10^23 x 2 ) ( avagadros number times no of Cl atoms) atoms are there in 278.2 g (Mr) of PbCl2 then 1.0x10^24 woud be there in : (278.2) * (1.0x10^24)/(6.02x10^23) put that in calculator and get the ans! hope this helps!

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