Chem 3411 Solution Set 5 - Mindanao State University - Iligan Institute Of Technology - 2010 Page 8
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14CHEM 3411, Fall 2010
Solution Set 5
4
Exercise 5.19b pg 202
Given
Calculate the masses of (a) KNO
(M
= 101.11 g/ mol) and, separately, (b) Ba(NO
)
(M
=
3
w,KNO
3
2
w,Ba(NO
)
3
3
2
1
261.32 g/ mol) to add to a b
= 0.110 mol kg
solution of KNO
(aq) containing M
= 500 g of solvent to raise its
0
3
solv
ionic strength to I = 1.00.
In terms of given variables, this is written:
M
= 101.11 g/ mol
w,KNO
3
M
= 261.32 g/ mol
w,Ba(NO
)
3
2
1
b
= 0.110 mol kg
0
M
= 500 = 500 g = 0.500 kg
solv
I = 1.00
Find
Calculate the masses of . . .
• (a) KNO
and
3
• (b) Ba(NO
)
3
2
to add.
Strategy
We’ll start with the definition of ionic strength (eq 5.76 on pg 196)
∑
)
1
⊖
2
I =
z
b/b
i
2
i
+
For part (a) we have two ions, K
and NO
, with charges of z = +1 and z =
1 respectively.
3
∑
)
1
⊖
2
I
=
z
b/b
i
2
i
[
]
1
⊖
⊖
2
2
=
(+1)
b
/b
( 1)
b
/b
+
K
NO
2
3
⊖
= b/b
with b as the concentration of KNO
; b = b
= b
.
3
+
K
NO
3
8
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