unit 3 aspirin sac

[jessdoc]

Hey guys, so I'm basically relying on winging everything to be even passing yr 12 chemistry right now ( ) and have the aspirin sac coming up. I've been told it's the easiest sac but... eh.

So I was wondering if someone could help me with excess and limiting in this and a few other questions? Help would be absolutely appreciated to help an aspiring doctor (with no chemistry skill... don't come to me for medicines ) lol

We began with
3.0g of salicylic acid
5mL of acetic acid
1mL of concentrated sulfuric acid
And we made 6.66g of aspirin (it was still wet, still have to use this number)

Questions I need help with are:

1. What is in excess? (and which one do I use for my mol calculations?) (I think it's salicylic acid?)

2. What could go wrong in this experiment?

3. How to find the number of moles of something when you're given the density (I don't know which one we're getting the density for though?)

Anyone who can help me out, would be very appreciated. Cheers.

[paper-back]

Salicylic acid is usually the assumed limiting reagent in this practical activity, so you use for the mole calculations (Probably why you weren't given the concentration of the acetic acid, as it was presumed to be in excess)

If you're referring to sources of uncertainty by stating "What could go wrong with this prac?" then there are a few such as;
- A loss of mass may have occurred during transfer of precipitate or salicylic acid
- Precipitate may not have been washed properly causing a residue of impurities on the precipitate
- Precipitate may not have been dried properly

For density questions, I believe you can just use the figure given to calculate the mass in solution upon which you can proceed with mole calculations
e.g. if density is given as 1.08g/ml for acetic anhydride solution and you have 5 ml of Acetic anhydride solution
Then 1.08 x 5 = 5.4mg/5ml (So 5.4mg in the solution)
n=m/M
n=5.4/M(Acetic anhydride)
n=....

[jessdoc]

Thankyou so much