The key difference between formality and molarity is that formality does not consider what happens to the substance after it is dissolved in a solvent when calculating the value, whereas molarity takes into account what happens to the solute once it is dissolved when taking the measurement.
Formality is the total concentration of a substance in a solution without regard to its specific chemical form. Molarity, on the other hand, is the molar concentration.
CONTENTS
1. Overview and Key Difference
2. What is Formality
3. What is Molarity
4. Formality vs Molarity in Tabular Form
5. Summary – Formality vs Molarity
What is Formality?
Formality is the total concentration of a substance in a solution without regard to its specific chemical form. In other words, formality is the number of formula masses of the solute divided by the volume of solution in liters. For example, if we dissolve sodium chloride 0.1 mol in a liter of water, it gives us a solution consisting of 0.1 mol sodium cations and 0.1 mol chloride anions.
The symbol for the abbreviation of formality is “F.” Formality can be simply described as a way of expressing the concentration of a compound in a solution. Sometimes, formality is similar to molarity when there is no dissociation into ions occurs. This is because the formality measurement does not take into account what happens to a chemical compound once it is dissolved in the solvent. Therefore, even if it is an electrolyte or non-electrolyte, the formality would be the same value.
What is Molarity?
Molarity is the molar concentration. This is the ratio of the number of moles of a substance in one volume of a solvent. Conventionally, the solvent volume is given in cubic meters. However, for our convenience, we often use litres or cubic decimeters. Therefore, the unit of the molarity is mol per litre/ cubic decimeter (molL-1, moldm-3). Moreover, we can indicate the unit as M.
For example, a solution of 1 mol of sodium chloride dissolved in water has a molarity of 1 M. Molarity is the most commonly used method of concentration. For example, we use it in the calculation of pH, the dissociation constants/equilibrium constants, etc. Moreover, we need to do the conversion of a mass of a given solute to its molar number in order to give the molar concentration. To do this, we need to divide the mass by the molecular weight of the solute. For example, if we want to prepare a 1 M of potassium sulfate solution, 174.26 g mol-1 (1 mol) of potassium sulfate should be dissolved in one litre of water.
What is the Difference Between Formality and Molarity?
Formality and molarity are important analytical parameters. The key difference between formality and molarity is that formality does not consider what happens to the substance after it is dissolved in a solvent when calculating the value, whereas molarity takes into account what happens to the solute once it is dissolved when taking the measurement.
The below infographic presents the differences between formality and molarity in tabular form for side by side comparison.
Summary – Formality vs Molarity
Formality is the total concentration of a substance in a solution without regard to its specific chemical form. Molarity is the molar concentration. The key difference between formality and molarity is that formality does not consider what happens to the substance after it is dissolved in a solvent when calculating the value, whereas molarity takes into account what happens to the solute once it is dissolved when taking the measurement. In other words, formality does not depend on the dissociation of solute after dissolving, while molarity depends on the dissociation of solute after dissolving
Reference:
1. “2.2: Concentration.” Chemistry LibreTexts, Libretexts, 12 Sept. 2021.
Image Courtesy:
1. “Chemistry-3533039 960 720” By despeakrit – Pixabay (CC0) via Commons Wikimedia