1. Calculate molality (m), in mol/kg, using the formula delta t = Kf * m.?
The Kf value for lauric acid is 3.9°C•kg/mol.
2. Calculate moles of benzoic acid solute, using the molality and the mass (in kg) of lauric acid solvent.
3. Calculate the experimental molecular weight of benzoic acid, in g/mol.
4. Determine the accepted molecular weight of benzoic acid from its formula, C6H5COOH.
5. Calculate the percent discrepancy between the experimental and accepted values.
THIS IS ALOT OF WORK SO I WILL REWARD 10 POINTS FOR THE 1ST ANSWER THE IS COMPLELTELY CORRECT WITH SHOWED WORK!
Atualizada:Mass of lauric acid- 7.94 grams
Mass of benzoic acid- 11.45 grams
Freezing temperature of pure lauric acid- 39.92 degrees celcius
Freezing point of the benzoic acid- lauric acid mixture- 48.37 degrees celcius
Answers & Comments
Verified answer
There seems to be a problem with some of the numbers, but I'll give it a shot.
1) 48.37 - 39.92 = 8.45
8.45 = (3.90) (molality); molality = 2.17
2) molality = moles solute divided by kg solvent
2.17 = (moles) / 0.00794; moles = 0.0172
3) molec wt = grams divided by moles
11.45 / 0.0172 = 665
Here is where I will stop. The correct molecular weight for benzoic acid is 122.12 (answer to number 4) and no molality based determination of benzoic acid's molec. wt. would give such an incorrect value (especially a classroom problem). Most likely, that means there is a mistake in the data you entered. I admit I could have made a mistake in my technique, but I've been over it and over it.
5) The percent discprepancy would be done like this:
(true value minus experimental value) divided by true value. Times it by 100 to get a percent and use the absolute value for your answer, do not include a sign. The true value is the 122.12 value.
You don't have the van't Hoff factor in your problem, but I don't think this is an issue. I'm pretty sure benzoic acid is undissociated in lauric acid, so the van't Hoff factor would be one.
So, go back and double-check the problem in the textbook and double-check my solution against the text (or a web site). Go to the teacher (or a tutor or the classroom guru) and ask for a bit of help.
HTH
Tilly took the words out of my mouth. So to speak. Or type, as the case may be. Only, I would have spelt and punctuated it correctly. It really annoys me when people steal my thoughts and then warp them to make me sound daft! Am I rambling? Sorry, what was the question again? Oh yes, I've always been a fan of McLaren (see what I did there,Tilly?) but I like drivers who display skill AND charisma. I like to see any British team or driver do well. But if someone goes about things with a interesting attitude or slightly different approach, then it doesn't matter where they are from or what team they are on (well, almost, but I'm getting to that..). I like to be entertained!! A good example of this is despite what he done at McLaren, I can't help but admire Alonso for his driving talent. But he's not my favourite, he's just an example of what I'm banging on about! Every show needs a villain and for me that is Ferrari, even though I'm a big fan of Kimi...arrgh!! The dilemma! I guess I'm a fan of the sport itself because teams and drivers come and go but the draw, the expectation, and the thrill is always there for me.. Every time.
Molecular Weight Of Benzoic Acid
Molar Mass Of Benzoic Acid