Tuesday, October 18, 2005

Determination of a Chemical Formula


Figure 1. Calcium Hydroxide solution with indicator.

The most common question I get when my students are doing a titration is when to stop. The endpoint of a titration is easy to overshoot. For that reason, I have taken a picture of what color your solution will be before, at, and past the equivalence point. You should stop titrating when your solution looks yellow, like the compound in the middle Erlenmeyre Flask.

posted by AaronRowe at 12:08 AM

3 Comments:

Blogger AaronRowe said...

Different titrations use different indicators. Some indicators only change color at one pH. Thymol blue, the stuff that we used here, changes colors twice at pH ranges that are very close together.

12:29 PM  
Blogger AaronRowe said...

You should post your 3x5 card question on the main page along with a list of what you have so far.

12:33 AM  
Blogger AaronRowe said...

Bridget,

Density seems to be the key to the whole problem here. If you have 1L of the solution, it will have a mass of 1886g. 38 percent of that will be HCl. Perhaps using a numerical method like that is the best shortcut.

If the density is 1.886 g/mL, then shouldn't .38 x 1.886 g/mL be the mass of acid per mL of solution? Divide by the molar mass of HCl, multiply by 1000, and you may have the answer in mol/L.

12:41 AM  

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