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National and Regional Contests
USA Contests
USA Physics and Chemistry Contests
National Chemistry Olympiad
2010 National Chemistry Olympiad
6
6
Part of
2010 National Chemistry Olympiad
Problems
(1)
2010 USNCO Local #6: Reagent for Precipitation
Source:
11/21/2012
An aqueous solution is known to contain
Ag
+
,
Mg
2
+
,
\text{Ag}^+, \text{Mg}^{2+},
Ag
+
,
Mg
2
+
,
and
Sr
2
+
\text{Sr}^{2+}
Sr
2
+
ions. Which reagent should be used to selectively precipitate the
Ag
+
\text{Ag}^+
Ag
+
?
<
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c
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a
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(
A
)
<
/
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a
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>
0.20
M NaCl
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(
B
)
<
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0.20
M NaOH
<
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(
C
)
<
/
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a
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>
0.20
M Na
2
SO
4
<
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p
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a
s
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(
D
)
<
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0.20
M Na
3
PO
4
{ <span class='latex-bold'>(A)</span>\ 0.20 \text{M NaCl} \qquad<span class='latex-bold'>(B)</span>\ 0.20 \text{M NaOH} \qquad<span class='latex-bold'>(C)</span>\ 0.20 \text{M Na}_2\text{SO}_4 \qquad<span class='latex-bold'>(D)</span>\ 0.20 \text{M Na}_3\text{PO}_4 }
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p
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−
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′
>
(
A
)
<
/
s
p
an
>
0.20
M NaCl
<
s
p
an
c
l
a
ss
=
′
l
a
t
e
x
−
b
o
l
d
′
>
(
B
)
<
/
s
p
an
>
0.20
M NaOH
<
s
p
an
c
l
a
ss
=
′
l
a
t
e
x
−
b
o
l
d
′
>
(
C
)
<
/
s
p
an
>
0.20
M Na
2
SO
4
<
s
p
an
c
l
a
ss
=
′
l
a
t
e
x
−
b
o
l
d
′
>
(
D
)
<
/
s
p
an
>
0.20
M Na
3
PO
4