Percent concentration and molarity are the most commonly used solution expressions in the histology laboratory. Interchanging these expressions involves defining percent concentration and molarity and performing ratio/proportion calculations.
Example:
What is the molarity of a 0.85% NaCl solution?
First, define the percentage solution: 0.85% w/v solution = 0.85 g/100 mL
Since molarity is defined in terms of g/L, convert 0.85 g/100 mL to g/L:
0.85 g/l00 ml = X g/1.0 L (1000 mL)
X = 0.85 x 1000 /100
X = 8.50 g/L
Once the number of grams of solute per liter is known, the molarity can be calculated:
Molarity = g of solute/GMW of solute x 1 liter
X = 8.5 g/GMW x 1.0
(GMW = Na 22.99 + Cl 35.45 = 58.44)
X = 8.5/58.44
Molarity = 0.14M
