Saline Solution

On 2/4/08 2:30 PM, "emaildave" wrote:

Physiological saline is a .9% solution of NaCl. (a) Express this in terms of molar or millimolar concentrations. (b) Make 125 mL of physiological saline.

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(a) 0.9% means 0.90g NaCl / 100 mLs

The above concentration is equivalent to 9.0g / 1000mLs or 9.0g / liter

The molar mass of NaCl is 23.0 + 35.45 = 58.45 g/mole of NaCl

(9.0g/L) / (58.45 g/mol) = 0.154 moles NaCl / liter or 154 millimoles/liter

NOTE:
1 Mole of NaCl contains 2 moles of ions (Na+ and Cl-). The above molar concentration is equivalent to:
(0.154 mol/L)(2 moles of ions/mol) = 0.308 moles of ions / liter.
This adjusted molarity is called “osmolarity”. “Colligative” properties such as osmotic pressure, freezing point depression, boiling point elevation, vapor pressure, etc. depend on osmolarity rather than molarity.

(b) (0.125L)(0.154mol/L)((58.45 g/mol) = 1.125g/L NaCl