68
Chemical Oceanography, 4th Edition
The total molality ∑m i /2, equivalent ∑e i /2, and ionic strength ∑I i /2 for sea water as a
function of S P can be estimated from
m = ½ (∑m i (S P /35) = 0.580283 S P /35)
(2.22)
e = ½ (∑e i (S P /35) = 0.627622 S P /35)
(2.23)
I = ½ (∑I i (S P /35) = 0.722627 S P /35)
(2.24)
The mean molecular M T and equivalent weight E T of sea water are given by
M T = ½ ∑ m i AW i = 62.793
(2.25)
E T = ½ ∑ e i EW = 58.046
(2.26)
For the grams of water in 1 kg of sea water,
g H 2 O = 1000 – 1.00488 S P
(2.27)
These results can be used to aid in the preparation of 1 kg of artificial sea water. A recipe
that can be used to make up artificial sea water is given in Table 2.4. It should be kept in
Table 2.4
Preparation of 1 kg of 35.00 of Artificial Seawater
Salt
Grams/ Kilogram
Moles/ Kilogram
Molecular Weight
Gravimetric Salts
NaCl
24.8780
0.42568
58.4428
Na 2 SO 4
4.1566
0.02926
142.0372
KCl
0.7237
0.00971
74.5550
NaHCO 3
0.1496
0.00178
84.0070
KBr
0.1039
0.00087
119.0060
B(OH) 3
0.0266
0.00043
61.8322
NaF
0.0030
0.00007
41.9882
30.0413
Volumetric Salts
MgCl 2
5.2121
0.05474
95.211
CaCl 2
1.1828
0.01066
110.986
SrCl 2
0.0149
0.00009
158.526
Use 1 molar MgCl 2, CaCl 2 , and SrCl 2 (standardize by AgNO 3 titration).
52.8 ml of 1 molar MgCl 2, 10.3 ml of 1 molar CaCl 2 , and 0.1 ml of 1 molar
SrCl 2 are needed. The densities of these solutions are 1.017 g/ ml, 1.013
g/ ml, and 1.131 g/ ml, respectively, for MgCl 2, CaCl 2 , and SrCl 2 solutions at
1 molar. The grams of water in each solution are given by
H 2 O = g SOLN – g SALT = ml × density – g SALT
Addition of Water
g H 2 O to add = 1000 – g H 2 O from MgCl 2, CaCl 2 , and SrCl 2