Science Buddies: "Ask an Expert"

I am working a project that founsd on this wedsite. The project is called The Chemistry of Clean: Make Your Own Saop to Study Soap Synthesis. I am having trouble on what exactly in supposed to be measuring the pH of. I couldn't find coconut oil so I used conola oil. I have also realized that if I try to measure what I think is the soap then how am I supposed to remove it from the cheesecloth. Here are the steps that I'm having trouble with:


"Boil for 20 minutes, or until all of the water has evaporated.
Carefully remove this beaker from the heat and allow it to cool.
Using the pH paper, test the pH of the crude soap. Record the pH in your lab notebook. Call it Crude soap.
Add 15 mL of distilled water to the soap mixture and stir it with a stirring rod.
Heat 50 mL of saturated sodium chloride solution in a 100-mL beaker until it is almost boiling.
If you are starting with the solid sodium chloride that is in the kit, weigh 15 g of sodium chloride and put it in a 100-mL beaker.
Add 50 mL of water and stir until dissolved.
Heat the salt solution until it is almost boiling.
Add the hot sodium chloride solution to the soap mixture. Use a hot pad or oven mitt, as needed.
Break up lumps of soap with a clean stirring rod.
Cover the beaker containing the soap mixture with cheesecloth and pour the liquid into a clear plastic cup. This is called decanting the liquid.
Measure the pH of the soap with a new pH paper.
Record the pH in your lab notebook. Call it Washed 1 time."

I've also noticed that when i boil the mixture for the first time some of it turns into a solid and the rest of it stays a liquid. I'm having a lot of trouble . Please help me soon

Hi,

The solid is the soap. The only reason to use the cheesecloth is keep from pouring the soap out of the beaker with the liquid. If you are careful you may be able to pour out (decant) the liquid without using the cheesecloth. If you must use the cheesecloth, after decanting turn the beaker right side up with cheesecloth still covering the beaker (the soap should be on the inside of the beaker). If it doesn.t fall off the cheesecloth into the beaker try tapping the beaker firmly onto the table a few times and tapping the cheesecloth stretched over the beaker top with a stirring rod to see if the soap will fall off into the beaker. If that still does not work then you will have to take the cheesecloth off the beaker and use the flat blade of a spatula or a table knife to scrape the soap off the cloth.. You might ask the person doing the cooking at you house for help. This is the same problem the cook has when pouring the cooking water out of a pot after cooking peas or pasta.

Good luck!

Barrett L Tomlinson

Thank You !I will use your advice the next time I try to preform the experiment. I have one more question though. As you explained the soap is the solid. So, what do I measure the pH of. I can't measure the pH of a solid with ph paper.

Hi:

I found several web pages that talk about ways to measure the pH of soap. The simplest is here: http://www.ehow.com/how_4706471_test-ph ... -soap.html but I found very detailed information here: http://www.newton.dep.anl.gov/askasci/c ... m00704.htm. It looks like you can test the pH of the solid soap. This information might be useful in the experiment. Thanks for your input.

Keith

Hi,

This is a very interesting project. The directions you have specify using pH paper to test the pH. To use the pH paper, you will need to wet the surface of the soap with a few drops of water and touch the pH paper to the surface so it is wetted. Then compare the color of the pH paper to the standard color. If you are going to use your soap, the final pH should be less than 10. If the pH is higher, you will need to wash your soap again.

Here is some background information on saponification. What is the difference between coconut oil and canola oil in making soap?

http://chemistry.about.com/library/weekly/blsapon.htm

Do you have pH paper? There are other options for measuring pH if you don’t.


Donna Hardy