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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: tomgreenschic on November 05, 2008, 05:55:41 PM

Title: soap and animal fat
Post by: tomgreenschic on November 05, 2008, 05:55:41 PM
One method used to make soap, NaC17H35CO2, includes the reaction between NaOH and animal fat, C3H5(C17H35CO2)3 according to the following balanced equation:

 C3H5(C17H35CO2)3 + 3 NaOH ----> C3H5(OH)3 + 3NaC17H35CO2

1. How many grams of soap would theoretically be produced by starting with 125g of animal fat?

I figured it out to be 387g. I'm just not entirely sure I did it correctly.

I found the molar mass of animal fat to be 890g and the molar mass of soap to be 918.

Any help would be GREATLY appreciated. Thanks much.

Title: Re: soap and animal fat
Post by: Astrokel on November 05, 2008, 10:53:36 PM
387 is correct
Title: Re: soap and animal fat
Post by: tomgreenschic on November 05, 2008, 11:23:42 PM
uh oh. are you sure? because I did it again and got 129 g of soap.
??? thanks so much.
Title: Re: soap and animal fat
Post by: Borek on November 06, 2008, 03:04:43 AM
387 was incorrect.

Your molar mass of the soap was not correct - formula of the soap is NaC17H35CO2, not 3NaC17H35CO2.

129 is OK.
Title: Re: soap and animal fat
Post by: Astrokel on November 06, 2008, 05:35:18 AM
Quote
uh oh. are you sure? because I did it again and got 129 g of soap.
 thanks so much.

Ye you are right as Borek has already said, as i worked out the question assuming your molar mass stated was correct.
Title: Re: soap and animal fat
Post by: Borek on November 06, 2008, 06:29:52 AM
Quote from: Astrokel on November 06, 2008, 05:35:18 AM
i worked out the question assuming your molar mass stated was correct.

That's why I like to check such questions with EBAS, it helps to catch stupid mistakes.

Although in this case error was obvious - molar mass of the soap must be about three times lower than the molar mass of the triglyceride.
Title: Re: soap and animal fat
Post by: JGK on November 06, 2008, 08:15:02 AM
Quote from: Borek on November 06, 2008, 03:04:43 AM
387 was incorrect.

Your molar mass of the soap was not correct - formula of the soap is NaC17H35CO2, not 3NaC17H35CO2.

129 is OK.

Where did the other 2 sodiums go? or should it be Na3C17H35CO2
Title: Re: soap and animal fat
Post by: Borek on November 06, 2008, 08:39:31 AM
Quote from: JGK on November 06, 2008, 08:15:02 AM
Where did the other 2 sodiums go? or should it be Na3C17H35CO2

To two OTHER soap molecules. Three are produced, each with NaC17H35CO2 formula, and molar mass of 306.46.