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User:Dbrogioli/Sodium chloride data

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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]

  1. ^ 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.
  2. ^ B. E. Conway (1952)). Electrochemical data. Elsevier. {{cite book}}: Check date values in: |year= (help); Unknown parameter |address= ignored (|location= suggested) (help)