What Is a Volumetric Flask?
A volumetric flask is a type of laboratory glassware used to prepare a solution of a known concentration with a very precise volume. It is characterized by a pear-shaped bulb with a flat bottom and a long, slender neck that has a single, finely calibrated ring mark.
Section 2: Key Features
The most important feature of a volumetric flask is the single calibration mark on its long neck, which indicates the exact volume the flask is meant to contain at a specific temperature (usually 20 °C). The narrow neck minimizes measurement errors when filling to the mark. Each flask is designed to be sealed with a glass or plastic stopper to allow for thorough mixing of the solution by inversion without spillage.
Section 3: A Practical Example
To prepare a 1-liter solution of 0.5 M sodium chloride (NaCl), you would first weigh out the precise mass of NaCl needed. This solid is carefully transferred into a 1000 mL volumetric flask. A portion of the solvent (e.g., deionized water) is added to dissolve the solid completely. Finally, more solvent is added carefully until the bottom of the meniscus (the curve of the liquid's surface) rests exactly on the calibration mark on the neck. The flask is then stoppered and inverted several times to ensure the solution is homogeneous.
Section 4: Importance in Chemistry
The high accuracy of volumetric flasks is crucial for analytical chemistry, where precise concentrations are essential for experiments like titrations and dilutions. Unlike beakers or Erlenmeyer flasks which have approximate volume markings, volumetric flasks are calibrated 'To Contain' (TC), meaning they hold the specified volume with a very low margin of error. This precision ensures that calculations based on the solution's concentration are reliable and reproducible.