Quantitative Chemical Analysis

In the next set of lessons, we will be looking at quantitative chemical analysis and the aim of these lessons is to help you become able to:

• Describe the fundamental aspects of titrations and gravimetric analysis.
• Perform stoichiometric calculations using typical titration and gravimetric data.

Introduction to Quantitative Chemical Analysis

In the 18th century, the strength (actually the concentration) of vinegar samples was determined by noting the amount of potassium carbonate, K₂CO₃, which had to be added, a little at a time, before bubbling ceased. The greater the weight of potassium carbonate added to reach the point where the bubbling ended, the more concentrated the vinegar.

Vinegar is a sour-tasting liquid containing acetic acid, obtained by fermenting dilute alcoholic liquids, typically wine, cider, or beer, and used as a condiment or for pickling (see image below).

Image credit: Conny Nilsson via Pixabay

We now know that the effervescence that occurred during this process was due to reaction with acetic acid, CH₃CO₂H, the compound primarily responsible for the odor and taste of vinegar. Acetic acid reacts with potassium carbonate according to the following equation:

\(\mathrm{2CH_3CO_2H}(aq) + \mathrm{K_2CO_3}(s) \longrightarrow \mathrm{KCH_3CO_3}(aq) + \mathrm{CO_2}(g) + \mathrm{H_2O}(l)\)

The bubbling was due to the production of CO₂.

The test of vinegar with potassium carbonate is one type of quantitative analysis—the determination of the amount or concentration of a substance in a sample. In the analysis of vinegar, the concentration of the solute (acetic acid) was determined from the amount of reactant that combined with the solute present in a known volume of the solution.

In other types of chemical analyses, the amount of a substance present in a sample is determined by measuring the amount of product that results.