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Solution preparation is an important step in many chemistry experiments. The key piece of equipment is the volumetric flask, a specially designed flask that measures one volume with high precision. Once the amount of solute to be prepared is determined, deionized water is added to the calibrated mark. Both solids and stock solutions (concentrated solutions with known concentrations) can be used to prepare a solution using a volumetric flask.
Solids
The moles of solute required is calculated using n = C V based on the desired concentration and the given volume.
The mass of solute is calculated using n = m / M.
A small amount of deionized water is added to the volumetric flask.
The solute is massed using a digital scale and transferred to the volumetric flask. A small amount of deionized water is used to rinse the weigh container, with the rinse added to the volumetric flask.
Deionized water is added to the volumetric flask until the meniscus of the solution reaches the calibrated mark.
The volumetric flask is stoppered and inverted several times to thoroughly mix the solution.
The solution is transferred to a labeled container for storage.
Above: The general process of creating a solution from a solid. From: https://d3rw207pwvlq3a.cloudfront.net/attachments/000/179/452/original/image.png?1618348709
Stock Solutions
The volume of stock solution, V1, needed based on the initial concentration of the stock solution, C1, the desired concentration, C2, and desired volume, V2, is calculated using C1V1 = C2V2.
A small amount of deionized water is added to the volumetric flask.
The volume of stock solution, V1, is measured and transferred to the volumetric flask.
Deionized water is added to the volumetric flask until the meniscus of the solution reaches the calibrated mark.
The volumetric flask is stoppered and inverted several times to thoroughly mix the solution.
The solution is transferred to a labeled container for storage.
Above: General process of generating a diluted solution from a stock solution. From: https://www.physicsclassroom.com/getmedia/55b6e90f-4984-4323-b221-442a60d8b0e9/Ch13L2b3.png?width=600&height=370
Serial Dilutions
A serial dilution is a technique to quickly generate several solutions from an orignal stock solution. Each solution is diluted by a factor of (e.g., 1/10) for each step. Volumetric flasks are used to increase the precision of the measurements.
Determine the fraction of the volume of the volumetric flask to be used. For instance, if a solution is to be diluted to 1/10 of the stock solution using a 250 cm3 volumetric flask, 1/10 of the 250 cm3 volumetric flask is 25 cm3.
Transfer the volume of the solution determined in Step 1 to the volumetric flask. Add deionized water to the calibrated mark. The new solution is 1/10 of the original.
Repeat the transfer and dilution of the previous solution until all solutions have been generated.
Above: An overview of how to perform a serial dilution. Each step of the dilution reduced the concentration 10x.
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