Check the concentration of the hydrochloric acid you want to dilute. This concentration may be described as a molar concentration or a percentage solution. Hydrochloric acid, or HCL, can be found as commercially prepared solutions or stock solutions (solutions made up previously in laboratories from strong solutions to act as a basis for further dilutions). The solutions are generally labeled in molarity, which is a measure of how concentrated the solutions are.
Calculate how much water and how much acid you will need to mix to create enough solution for your needs. To do this, use the following equation:
volume A x moles per liter A = volume B x moles per liter B
where A refers to the initial solution and B to the desired end solution.
For example, if the initial solution has a molarity of 2M, and you want a liter of an end dilution of 1M, you will need to mix 500ml of the initial solution and 500ml of water. This figure is calculated by inputting the known data.
volume A x 2 moles per liter = one liter x 1 moles per liter
If you switch it around, it becomes:
volume A = 1 / 2 liters
which is equivalent to 0.5 liters or 500ml of the initial solution you require. When you subtract 500ml from the required end volume of one liter, the result is 500ml, which is how much water you need to mix with the initial solution.
Put on personal protective equipment (PPE). Directions as to what PPE you will need can be found on the material safety data sheet (MSDS) of the HCL you are using, and you will also need to comply with any extra PPE and safety requirements of the laboratory you are working in. Some of the PPE you may require includes splash goggles, gloves and protective clothing.
Choose a flask that can hold the amount of diluted solution you require. Place the materials in an approved location, such as a lab hood or a bench top, depending on laboratory practice. Measure the required amount of deionized water into the flask using a pipette. Read the measurements from the bottom of the meniscus (the curved line of the top of the liquid inside the pipette). Use another pipette to draw up the amount of HCL you require. A pipette is more accurate than a graduated cylinder. Slowly add the acid to the water. Never add water to acid. Swirl gently to mix before use.