500 g of a 5% aqueous hcl solution assuming that a 37% hcl solution. It must include safety precautions in the answer, and the procedure.
Tue, 2012-01-03 20:56
37% HCl is the concentrated hydrochloric acid reagent, as concentrated as you can buy it. (The pure HCl is a gas that comes in a gas cylinder, and chemists call it hydrogen chloride).
I assume you want to know how to make a 5% w/w solution from the 37% HCl reagent.
(500g solution)(5g HCl/100g solution)(100g reagent/37g HCl)=67.6g reagent
That would mean that you need to mix 67.6g of 37% HCl with 432.4 g water.
NOTES and PRECAUTIONS
As soon as you open that bottle of 37% HCl, fumes will start coming out. You need to do it in a fume hood.
As the 37% HCl and the water mix, heat is generated, a lot of heat. If you start adding water on top of the acid, you'll soon have a boiling solution of fairly concentrated acid. You are always supposed to gradually add the acid onto the water. The heat will be released gradually, as the acid is added, and the temperature of the water (or very dilute acid) does not increase as much as if the same amount of heat was absorbed by concentrated acid. If the mixture started to boil, you could stop adding the acid. And if the boiling solution splashed, it would not be as concentrated.
No matter how carefully you work, you need a lab coat, gloves and safety glasses (or goggles). Wearing personal protective equipment (PPE) is very important for a chemist. It protects you from lab dangers, and from the danger of being fired for not wearing it.
Weighing the 37% HCl reagent is not practical. The balance risks getting corroded by the fumes (from the HCl and anything else in that hood). It's better to measure the amount of HCl reagent by volume. The labels on reagents state actual assay (it could say 36.9% assay), and density ( for example, d=1.18). So you could calculate volume for 67.6 g of your HCl reagent and measure by volume. That's how I would do it, anyway.
Weighing the water is not very practical either, but no calculations are needed because 1.00 gram of water is 1.00 milliliter of water.
If someone tells you to make a 5% solution, it does not need to be 5.000%. Otherwise, they would have included the zeros.
That means that probably measuring 432 mL of water as well as you can with a 500-mL class A, calibrated to contain, graduate cylinder is probably accurate enough.
The prepared solution should be stored in a closed container, and clearly labeled. The label should include a complete description (5% w/w aq. HCl), date of preparation and initials of preparer. Storage conditions, safety precautions and expiration date may be required. Lots of reagents used and/or a laboratory notebook reference may also be required.
Rinse glassware/equipment used, disposing of the rinsings into liquid hazardous waste containers as needed, and set rinsed glassware/equipment to wash as needed. Wet wipe and dry the outside of the reagent containers. . Wet wipe and dry your work area as needed (or safely dispose of the protective pad you put on your work area).
To measure the concentrated HCL reagent by volume, we need to calculate the volume needed using the density.
(67.6 g HCl reagent)(1.00mL HCl reagent/1.18g HCl reagent) = 57.4mL HCl reagent
So I would measure 430 or 432 mL water and 57, or 57.4 mL of 37% HCl. I would add the 37% HCl to the water slowly. I may do it in a beaker or in a wide mouth bottle. I would mix , probably on a magnetic stirrer, with a magnetic stir bar added into the water before adding the acid.
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