Class-
l
halc
I
{
Using conversion factors to find the number of atoms from a known
mass of a substance.
Sample Problem
4 How many atoms are there in 5'00 e of copper?
The first one is formed by writing 1 mole of
copper, 63.5 g, in the de4ominator'
copper in the numerator and the gram atomic mass of
Solution Two conversion factors
5.00
g Cu
are
needed.
,. I
mole Cu
63.5 g Cu
=
0.079 mole Cu
The second factor is formed by writing the Avogadro number, 6'02
numerator and I mole of copper in the denominator.
0.079 mole Cu
y 6.02 x
uoms = 4.74
l moleCu
10P
x
x
103 atoms, in the
lG2 atoms Cu
Both factors can be used in one step as follows:
5.00gCu
x lmoleCu 16'02xlG'atoms
= 4.74 x
1ff2 atoms Cu
l moleCu
63.5 g Cu
Pracffce prcblems
2.
Solve each of the folloting problems. In the space below each problem, show a labeled
at
setup. Do any necessary arithmetic on scrap paper' Write your answers in the spaces
the right.
a. What is the mass of 1.75 moles of zinc atoms?
f f " ?s,r,ul **Y .q::L3,\> lrl 3 Zn
b. How many moles of atoms
'll,CI rJ ftt
are there in 42.0 gr:rms
L,T> ,orc( ( ".,
d. How many
(
1*# \=
atoms are there in
1.
50 moles
c.
atoms?
l,stornrl fll
b.
Fl\t| ' st*rn&l 4l
( A7""t
)*
c. What is the mass of 0.675 mole of copper
c.
of aluminum?
"-\],,q ,^
(,
I e,q.J Lo
d.
of carbon?
?.
c3{ lJ=*:,*br",
calts,us
|,5c*nl C (- t, -os,xwt,3..1-,*r\= '.,,cIAt;;J*,-.
I tt'tts I
e. How many
'V
)
moles of atoms are there in 7.50
,5u y 6!t*!',,,71
l-* Lf , ''"Jf,,,orx
x lff'
atoms of iron?
rr!3*h*t
\
)
e.a,alJ5. n*l
CI,GlA{
re?ciI
Fe
91
r{
f. What is the mass of 1.25 x
t. ,\1,1,1 fut
l0n atoms of nitrogen?
l.?r4,31^h*'(##frff)=
g. How many atoms
are there
an,\g N
s.3 ,Yv{i3s', qlo'-s
in 18.0 grirms of silicon?
r-A t ',q'x4lq
:-1-,gr.xt33ulo*> S',
l9,o*
-' ft l,t,l3
'---J s,
Jt t r',.wt )- '
h. Whuisthemassof6.25 x l0'oaromsoflead?
fr. O,7lfg ?t
b,A€xt&Zh*s pt
(%XX\_
o,l's3pb
i. g ,qrtrJt
i. Howmanyatomsarethereinl.35 x lo2mole ofneon?
f
j.
,35 xl6'nol Ne (b'oz x,o=3^lu*s)
./ =
I .7',n t
Whatisthemassof 8.55
t.sr
92
x ,63
rrol
.
x
103
g,
t3yto'tolo*, lW
i.
mole of silver?
bJ (X)
\/,
=
,A6
o"773q
J
h
CI,3?3^
+J
ahns
Date-
Classthe Avogadro number, 6.02
The second factor is formed by writing
numerator and I mole CHIOH in the denominator'
{
1.56 moles
6.02
CH'OH x
x
1023
molecules
C!g'QFI-
=
x
9.39
1023
x
molecules, in the
10" molecules
t mole CH.OH
Thethirdfactorisformedbywriting4atomsofhydrogeninthenumeratorandlmolecule
CH:OH in the denominator'
9.39
x
4 atoms
l0r'molecules CHIOH x
All three factors
H
=
3.76
x
l02o atoms
H
I molecule CHIOH
can be used in one step as follows:
CH'OH x 6'02 x
50.0 g CH'OH a 1 mole
32.0 e CH.OH
4 atoms H
10P' molecules CHgOH
I
1 molecule CH,OH
=3,76x 102' atoms H
mole CH'OH
Practice Ploblems
setup'
the space below each problem, show a labeled
solve each of the following problems. In
right'
the
at
paper' write your answers in the spaces
Do any necessary arithmetic on scrap
'' l;ffi'.[;,iT;13"1il.1#?1,ij,tj;?flfi';"tecuresinthesampre.
*/Ltu'6')::'oi8't
/Arv\ blud.t* z-{',,-\+ tfaa,'\ rls. cc l4ts"'.,
\ t o"
(#
ts
3m'l
4. a.
o,t53''ol
Nti
7/)'-t
HzSaI
'I"z
b.7_,7wo14 ltrrlr',t.
c ko'zS
b. What iJtrre numUer of in"ote''ules of H'SO. in the sample?
u,e.t (':: Yi->t'"-\: q,]l x- h:7-,*u lec; Its i'l-'sa,
'ii',"'s*f;l
there in the sample?
".
c. H9w many atoms
1,7r ..te"n,olat, lltSa, F-et\
' l,,riS /t;uu.{orn*
o.)s3 m,t
L
are
d. Find the number of oxygen
d.
atoms in the sample'
_>3
1@-'
a.zl t,,a'trrolu*.Hr*"( (
3.rY ri;:
5. A sample of C.FLClz contains 4'80 x 1S' molecules'
a. How manymoles of G.FLCL molecules arethere in the sample?
( .,('
I
,l,gu 4p3z7q,rloc. .t
\ (d ,c.; .\t.c)- ,n"
=
-=-\ =
c- )
tc:-
b (i t'o
2 ll
a
\
e*
(,t]rrt,
O " oV47 ruul
V !y'*"1
t"t -\
f:J \\**
I ,'"ra i J
'{ (t'
x/ $en
cxt<,$15
b.
P,o7ciV CIal A*H,.t&tz*
{
,\
a{CIj-s
s. a.o '?Hlme I
b. What is the mass of the samPle?
Mrv\ L*H"r cl u
3.aut,J=oru,*n
"\ }
ll.?s tb+,{tL
ll,7*u L*Hy tlz-z(s-s.
s)
c. How many atoms of chlorine
t/"f,r; xto T*ot*.,
d. How many
t1.<t:a
are there in the sample?
/zI titni:) *l**
le.L"
7z
LC
* to
.
,Yf
atoms of carbon are there in the sample?
* rr!t,,,a",1€-,
( #')
x,.r*L+*'',
6. A sample of (NHo)zSOo contains 0.750 mole of (NFL),SO. formula units.
a. What is the mass of this sample?
M/rl Qvx.)*-lil = i?'o *\i-
ou lsL)
n|or*5
c-l
,,y1.;,!
gd
r'c')
(2"''\
+- t
(v**!s.q ( '#,\= E-
b. 'How many moles of NHr'ions are there in this sample?
,)5orwl (t"W
|
o. t,ls fuv,Y,r
". z 37*.u1
;'rd'''4 13
6l
-=t
/\- z Nr+uts \,75D.rr-t WH.,\ogr,t ||:
I (v ur)rS(t1 J
c. Find the number of (NHo)rSOo formula
u-
'
,.ia
14,
,n*
|
N t+,+ J-
units in this sample.
a2
\=lv, 5)-xtu
LtWLaI
d. How many hydrogen atoms are there in this sample?
,l
.s'Axr,*tt f.,,'tr.tJ.-.:d
{1
: J
nv'1 ','io'",'i\
#'t': Y, v't ' f
a. How many
of 15.5 grams.
moles of Ba(ClOrL are there in this
b. How many
moles of oxygeiiat6rils
,b
.,J
tx
,J"{ llyd.rrSre-i
.o.ko;s
7. A sample of Ba(ClO:), has a mass
sample?
7. a.
-n{:s.r)
M//\ B*r{e-rc:}.. = r { r3*) +
+ A, (tu,"') = 3r*t1 3y7,t
frs,s* {i*i [*io=). )( # ) --
f)"
crs-r
o
.tsct
ire thFe
inffi****-T
f 4*l*,"**\_ (bfuy.
r
, ?.r1-,u-L ) =
c. How many Ba2' ions are there in this sample?
4r , D-s-r
d.
96
o ,.ilv,l b.-
(.
erc,,\, I
".- \
1'* t
I frro,
r.
t*">F
gr,
lcto"\,
c._
\/f ,a;x tclSBh'r,o,rs\
Y::::'"'"T::'i,lT:":i:T::T:l'lJI"-::1i::t'_t""orBa2'
-= 13 .c ltrc
, re*r