The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Chemistry concentrations

2003

How do you increase or decrease the molarity/concentration of an acid. Can you just add water to it, e.g., say you were given 10% Hydrochloric acid how would you get 4 equally spaced lower concentrations of that. e.g., to get 5% hydrochloric acid do you just add half water and half acid of your specific amount of 10% HCl?

This is for a school experiment.

Please help, thank you.

Rachel J.
- Christchuch, Methven, New Zealand

---

The theory of your answer is handled quite nicely in a normal chemistry book, even current high school books. You do not state what quantity you are working with, uL or mL or L. It would be much easier to measure and calculate if you had more. IE: 100%, 90%, 80%, 70%,60% and 50%. If I understand your "4 equally spaced", that would be 100%, 87.5%, 75%, 62.5% and 50%. Example, use 12.5mL of water and add 87.5 mL of acid to it. Note that you will not end up with 100.00 mL of total solution, but very close to it. Remember, acid into water - NOT water into acid unless it is under 1 Molar or Normal, and then with caution. Sulfuric generates a large heat of solution, i.e., it can get darned hot with concentrated acid.

James Watts
- Navarre, Florida
2003