Question

"What mass of PbCl2 contains 1.0X10^24 atoms Cl?"

Answer 1

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

Answer 2

composition* not plural

Answer 3

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?

Answer 4

whats the mass of that many Cl atoms?

Answer 5

71

Answer 6

or i am not sure :(

Answer 7

\(n=\dfrac{N}{N_A}=\dfrac{1.0*10^{24}}{6.023*10^{23}}\)=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

Answer 8

good so far?

Answer 9

somewhat yes

Answer 10

how to go from that to eventually 230g?

Answer 11

and what does m stand for in the second equation

Answer 12

m = mass (in g), M=molar mass

Answer 13

so, 26%*m=58.847 g

m=58.847g/0.26=226.3346153846153846

Answer 14

i didn't round, so my answer is a bit off from what you expected (230 g)

Answer 15

thanks, i'm going to try to write it out on paper to see if i understand :). Ill be right back

Answer 16

okay !

Answer 17

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?

Answer 18

and the 1.66 moles is moles of Cl? and not PbCl2?

Answer 19

these equations?

\(n=\dfrac{N}{N_A};\;\; m=n*M\)

Answer 20

yeah 1.66 moles of Cl because you're using the amount of atoms of Cl not the whole molecule

Answer 21

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!

Answer 22

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

\(m_{backpack}=\dfrac{10g}{0.5}\)

Answer 23

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!