User:Dbrogioli/Sodium chloride data
General values[edit]
Standard temperature: 20°C
Solubility at 20°C: 5.43 M
Molecular weight: 58.44
Conducibility of 10 mM salt solution: 0.1156 S/m
Definition of NaCl solutions[edit]
Solution | Concentration | Weight fraction (g/g) | Volume concentration (g/L) |
---|---|---|---|
Fresh water | 20 mM | 0.1167 % | 1.169 g/L |
Sea water | 500 mM | 2.868 % | 29.22 g/L |
Evaporation brine | 5 M | 24.60 % | 292.2 g/L |
The molarity is expressed as moles per L of solution; the weight fraction as g of salt per g of solution, and the volume concentration as g of salt per L of solution, not per L of solvent.
Definition of multi-ionic solutions[edit]
Table of concentration of ions in sea water
Density: 1.0255 kg/L.
Recipe for sea water:
Salt | concentration (mM) | Weight fraction (g/g) | Volume concentration (g/L) |
---|---|---|---|
[NaCl] | 500 | 2.849 % | 29.22 g/L |
[MgCl2] | 25 | 0.2321 % | 2.380 g/L |
[MgSO4] | 30 | 0.3521 % | 3.611 g/L |
[KCl] | 10 | 0.07269 % | 0.7455 g/L |
[CaCl2] | 10 | 0.1082 % | 1.110 g/L |
[NaHCO3] | 2.5 | 0.02047 % | 0.2100 g/L |
Comparison with typical concentrations of ions:
Ion | Obtained concentration (mM) | Typical concentration (mM) |
---|---|---|
Cl- | 580 | 583 |
Na+ | 502.5 | 500 |
SO4-- | 30 | 30 |
Mg++ | 55 | 57 |
Ca++ | 10 | 11 |
HCO3- | 2.5 | 2.5 |
Density[edit]
Density of NaCl solution in water (needed to prepare solutions at given molarity):
where:
Water density: = 1 g/cm^3
NaCl molar mass: M = 58.44 g/mole
Partial molar volume of NaCl in water : 20.9 cm^3/mole
Note: c in M; other in cgs units.
The parameter has been obtained by fitting data provided in [1])
This formula has a precision of 0.2%. Since it is nearly linear, we assume that mixing respects volumes, that is, if we mix a volume Va at concentration ca and a volume Vb at a concentration cb, the resulting solution has volume Va+Vb (this is not always true for any solution).
Osmotic pressure[edit]
The van 't Hoff formula is an approximation giving an error of the order of 8% in this case. A better approximation is:
where:
is the osmotic pressure
R = 8.314472 J/mol/K
T is the temperature, 20°C
a = 0.93
b = 0.0113 /M^2
Note: c in M; b in 1/M^2; other in MKS units.
The parameters a and b are obtained by fitting data provided in [2]
The formula has a precision of 1%.
Gibbs free energy[edit]
Using the parameters a and b given in the previous section, the Gibbs free energy density (i.e. the free energy of a unity volume of solution at a given concentration c) can be expressed up to a constant and linear term:
where and are irrelevant for calculations concerning mixing of solutions.
The Gibbs free energy density relative to a concentration can be calculated:
Note: c is in M; results in MKS.
See the page on thermodynamics for definitions.
There is an applet for the calculation of the free energy of mixing of two solutions of NaCl
References[edit]
- ^ Landolt-Bornstein. "1.2". Group IV: Physical Chemistry; Mechanical Properties - Densities of Liquid Systems - Densities of Binary Aqueous Systems and Heat - Capacities of Liquid Systems. doi:10.1007/b20004. ISBN 978-3-540-08272-9.
- ^
B. E. Conway (1952)). Electrochemical data. Elsevier.
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