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How to Make 3 Molar Hydrochloric Acid

Hydrochloric acid is a strong mineral acid and invaluable laboratory reagent. For industrial and lab use, hydrochloric acid is generally sold as a highly concentrated solution that can be diluted to yield solutions of a desired concentration. Many hardware stores also sell hydrochloric acid but refer to it as muriatic acid, an older name for the same chemical substance. While diluting hydrochloric acid is fairly easy, it's important to be aware that the concentrated solutions release hazardous vapors, so you should only attempt this procedure in a fume hood or other well-ventilated area and with appropriate protection.

Things You'll Need

Fume hood
Goggles and gloves
100 mL volumetric flask
Deionized water
Concentrated hydrochloric acid
Beaker
Graduated cylinder
Glass funnel

Instructions

- 1
  Write down the concentration of your starting HCl stock solution. Typically the concentration is expressed in % w/w, i.e. the number of grams of hydrogen chloride in 100 grams of solution, and it's usually between 30 and 40 percent.
- 2
  Divide the concentration by 36.46 grams per mole. If the concentration is 36 percent, for example, divide 36 by 36.46 to yield 0.9874 moles per 100 grams of solution.
- 3
  Multiply the result from your last step by 10 to convert it to moles per kilogram, then multiply it by the density of the solution. The density may be marked on the stock solution. If it is not, you can assume a 30 percent solution will have a density of approximately 1.15 kilograms per liter and add 0.005 kilograms per liter to this figure for each additional percentage point above 30.
  
  To continue the example, if you multiply 0.9874 by 10, then multiply it by a density of (1.15 + 6 x 0.005) = 1.18 kilograms per liter, you obtain a concentration of 11.65 moles per liter.
- 4
  Take the number 0.3 and divide it by your result from the previous step to determine how much concentrated HCl you will need. You're using the number 0.3 because it's what you get when you multiply 3 moles per liter (the concentration you are trying to obtain) by 0.1 liters (the amount of solution you want to make).
  
  To continue the example, 0.3 divided by 11.65 = 0.0258 liters or 25.8 mL. This means you will need 25.75 mL of the concentrated hydrochloric acid solution to make your dilute solution.
- 5
  Put on your goggles and gloves. Make sure the fume hood is operational, and perform the remainder of the procedure inside the hood.
- 6
  Add a little deionized water (roughly 25 mL or so) to the volumetric flask. Use the glass funnel if necessary.
- 7
  Pour some of the hydrochloric acid into the beaker, then recap the container tightly. Pour the acid from the beaker into the graduated cylinder until you have a volume roughly equivalent to the amount you calculated you would need.
- 8
  Position the glass funnel in the mouth of the volumetric flask. Pour the acid from the graduated cylinder into the flask. Add a little deionized water to the graduated cylinder as a rinse, then pour this rinse water into the flask. Cap the flask and swirl gently to mix.
- 9
  Uncap the flask and add more deionized water until the bottom of the meniscus reaches the fill line. Recap the flask and invert to mix. The flask now contains 100 milliliters of a 3 molar solution of HCl. Dispose of any excess HCl in the beaker in accordance with your laboratory's procedures for hazardous waste.

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