[HilltopHood]

In the exercises, here is how the questions are phrased:

Show how you calculated your values.

B. The concentration of the acetylsalicylic acid solution in the 2.00 mL aliquot:

My work: 0.002567894/0.002L = 1.283947 mol/L

C. Since molarity is an intensive property, the concentration calculated in (B) is also the concentration of the acetylsalicylic acid solution in the 250.0mL sample. Using the answer from (B) calculate the number of moles of acetylsalicylic acid in the tablet:

My work: (1.283947mol/l)(0.002L) = 0.002567894 mol

Am I missing something obvious?

[Borek]

B. The concentration of the acetylsalicylic acid solution in the 2.00 mL aliquot:[/b]

My work: 0.002567894/0.002L = 1.283947 mol/L

And how are we going to know what is the problem and where did you got these numbers from?

But I can confirm your calculations - 0.002567894/0.002=1.283947, that's perfectly OK 

[Arkcon]

It would also save us some confusion if you used the correct number of significant figures.

[HilltopHood]

B. The concentration of the acetylsalicylic acid solution in the 2.00 mL aliquot:[/b]

My work: 0.002567894/0.002L = 1.283947 mol/L

And how are we going to know what is the problem and where did you got these numbers from?

But I can confirm your calculations - 0.002567894/0.002=1.283947, that's perfectly OK 

Background

In the experiment a solution of known concentration that contains an salicylato iron(III) complex is prepared by dissolving a known amount of aspirin tablet in sodium hydroxide, which is then added to a solution containing Fe3+(aq).

Absorbance measured using a colorimeter (A = .305). Using the Beer's law plot from part A (y = 672.73x + 0.0286), determine its concentration and then "back calculate" to find the number of mg of acetylsalicylic acid in the aspirin tablet. Compare with that on the label.

Steps I took:
1. Put aspirin tablet in 125-ml flask
2. Added 10ml of 1 M NaOH(aq), boil
3. Transfer resulting solution to 250-mL volumetric flask, dilute with water to 250.00 mL
4. Perform gravity filtration on 10 mL
5. Pipet 2 mL of this solution into 50-mL flask, dilute to 50.00 mL mark with 0.02 M iron(III) chloride solution
6. Measured mean absorbance
7. Calculate concentration of tetraaquasalicylato iron(III) complex in this solution using slope of the line from Part A (given), calculate concentration of acetylsalicylic acid (in 250-mL flask), moles of acetylsalicylic acid, mass of acetylsalicylic acid in the tablet

Also, here's part A that I calculated

A. The concentration of the acetylsalicylic acid solution in the 50.00 mL sample:

y = 672.73x + 0.0286

305 = 672.73x + 0.0286

x = 0.000410863 = 4.109*10^-4mol/L

[Borek]

305 = 672.73x + 0.0286

x = 0.000410863 = 4.109*10^-4mol/L

It is a basic algebra - and it is incorrect. Easy to check:

672.73×0.000410863 + 0.0286 = 0.305

so you are exactly 1000 times off.

Unless x is not expressed in M, but in mM - but if so, you are again wasting our time not showing all necessary information.

[HilltopHood]

305 = 672.73x + 0.0286

x = 0.000410863 = 4.109*10^-4mol/L

It is a basic algebra - and it is incorrect. Easy to check:

672.73×0.000410863 + 0.0286 = 0.305

so you are exactly 1000 times off.

Unless x is not expressed in M, but in mM - but if so, you are again wasting our time not showing all necessary information.

Sorry, meant 0.305.  the x value is still the same 

Anyway, here is the data sheet.  Hope that provides enough info.  Chemistry was never my best subject.  Pretty sure the last four are completely wrong:
http://i.imgur.com/Rtu2Yan.jpg?1