I'm helping someone with a chem assignment. They have to bake cookies but the recipe is given in moles. We need to find the chemical formula, calculate molar mass, and then convert to grams, the various ingredients.

My question - is there a difference in the chemical formula and molar mass between white sugar and brown sugar? Haven't been able to find it anywhere... I easily found the chemical formula of white sugar and it's straight forward to find molar mass... but nothing on brown sugar. I know brown sugar is just white sugar plus molasses, but different brands have more or less, some mix it in whereas others coat the top of the crystals etc. Do I just disregard the molasses?

Brown sugar isn't as specific as simple sugar.

There are a dozen different kinds and the chemical makeup varies from brand to brand as does the amount of molasses, which is what gives it it's brown color.

So yes, there is a difference. I doubt you will find a chemical formula for brown sugar, and if you do it probably will be a different kind than what you are using.

Cheat and use regular sugar!

Google was a bust???

Google the brand you are using and the molasses percentage then the molasses chemical formula, then factor that into your regular sugar formula.

you would need (or assume) the proportion of molasses and white sugar in brown sugar assuming that that is what you mean by "brown sugar" ie sucrose + molases and not a "naturally occurring" brown sugar.
However: molasses is a combination of many chemicals and iirc it's only about 1/2 sucrose on it's own and the other 1/2 is amino acids and other sugars.
Given that this question is probably written by someone who didn't think it through/doesn't really know a lot about biochemistry I would just "pretend" that brown sugar is sucrose and proceed accordingly.

Good luck with milk and flour (especially flour) btw:)



<off topic mini rant>
The problem with these types of questions is that they reward people who know too little or people who have way more knowledge about such things than can be reasonably expected from them. Brighter students will realize that molasses is not simply sucrose and try to be more exact but not be able to for example. Taking those students from that stage of learning to knowing how to make simplifying assumptions and assessing their impact is a *huge* leap which for more complex things is a challenge for most adults (people pay a lot of money for this skill). This is why I did so miserably at biology in hs.. I knew too much to fall into the "simple" way of thinking but wasn't good enough to make that conceptual leap.. </rant>

mr ford must be an engineer.. that's the type of answer one would expect from them :P
practical and (hopefully) functional but not necessarily scientifically correct:P

Close nuff!

Yeah, I'm going to just go with sucrose...

The ingredients are listed as:

0.30 moles of white sugar
0.60 moles of packed brown sugar

Convert brown and white sucrose (the guy gave away the answer to a previous question which was to find the chemical name for sugar) to grams and then to cups using the conversion 1 cup = 205.404 grams.

I'm just going to use C12H22O11 for both.

Oh, and milk and flour is given as cups. Just need sodium bicarbonate and NaCl which are straight forward. The only other strange one was converting butter from volume to length of stick... which is so strange and has nothing to do with chemistry. The teacher even goes so far as to tell students to use length x width x height of a stick of butter at home to do this. This particular question is all math - and even then, they're given the formula for volume of a rectangular prism as if a grade 11 chemistry student wouldn't already know this.

Other fun things - latin name of the plants that flour, oatmeal, and chocolate come from? I found wheat = triticum aestivum, oat is avena sativa, and the cacao tree is theobroma cacao is Seems like mostly a pointless assignment disguised as a fun activity to bake cookies.

brown sugar has 3/5ths the molar mass as white sugar





now we can make this thread about racism!

Brown sugar tastes better than white sugar.

black sugar doesnt matter

The answer is 42.

http://www.livestrong.com/...wn-sugar-nutrition-facts/

Not sure if this helps, but afaik you can substitute white and brown sugar interchangeably in most cookie recipes by volume. The resulting cookies will be softer and darker as you add more brown sugar.

For cooking purposes, I'd just consider it sucrose, as that's what like 90+% of it is anyway

Naah. If the answer was 42 then we wouldn't know the question.

I quite like this assignment - especially for chemists who like things precise.

Chemistal analysis has crept more and more into cooking thanks to characters like Heston Blumenthal but there has to be room for pragmatism.

At the end of the assignment ther must be COOKIES.

I think the teacher intended that they assume both are sucrose. The conversions work out such that the given moles of sugar would be equivalent to half a cup, and it requires double the brown sugar resulting in one cup. All of the other calculations (salt = 1/4 tsp, baking soda = 1/2 tsp etc.) are nice and even numbers, and my assumption is that breaking down brown sugar into sucrose + molasses wouldn't result in such a nice round number like 1 cup.

I'll explain to her why in reality brown sugar is different, and also why it's difficult to accurately measure it and why her teacher likely intended them to treat them both the same.

Brown sugar is ranked too high.

well if you want to be really anal about it, white sugar from the store is not 100% pure sucrose.. there is an acceptable level of contaminants in it which would probably increase the molar mass slightly.. but lets not go there:p

Also sugar will have absorbed some water from the air (which actually can be adjusted for very accurately since it does so in a predictable way if you know the temperature and pressure of the room) :P

Did I mention I hated analytical chemistry?:P

ps. most hs chemistry is essentially electrochemistry just under a variety of names and differing formulas just to annoy you. Then you learn that most of those annoying titration and acid/base labs are actually much more easily done with a volt meter. :P


*ducks*

Nice catch - the half cup point.

Should you be helping quite this much?

No, you're right. I'm not giving her the answers, I just want to have them myself and have worked through them so that I'm comfortable explaining them. I usually just stick to math when it comes to anything above grade 8, but there are some parts of chemistry and physics that I feel comfortable with at the high school level. The student sent me her assignment and asked if it's something that I could help her with... but I haven't done this stuff in a while and wanted to make sure I was doing it right before explaining it to her.

Sounds good.

I have a great admiration for teachers - and teaching an able pupil must be a joy. Not something I could ever have done, though. You have to give more of yourself than I think I could have managed.

This is one of those questions from a teacher that has watched to much CSI on TV without having any real world experience.

FWIW, the volume to stick-length conversions are generally written on the wax paper that a stick of butter comes in. One stick = 8 TBSp = 1/2 cup = 1/4 lb

(that is unmelted volume, it shrinks a bit if you melt it due to entrained air)

Thank you. At times it feels like you have to give more than you have, but overall I love it.

you lot can make pipe bombs with me any time ;P