[Teeny]

My AP Chem class performed this chemistry lab on thursday. I'm pretty clueless on how to do the calculations, and this site has been helpful before, so I was wondering if you guys might be able to guide me.

http://www2.vernier.com/sample_labs/CHEM-A-10-COMP-Keq.pdf
Above is the exact copy of the lab information I help.

For the prelab exercise, I got these numbers.

0.00M
8.0*10-5
1.2*10-4
1.6*10-4
2.0*10-4

And then for the data table of part 1 & 2, I got the following numbers for the absorbance rates, respectively:

.013
.030
.036
.039
.044
unknown, part II: .003

best fit line equation for the part 1 standard solutions: aborbance = 251.85 [FeSCN]

For part III data table, i got the following numbers

.008
.143
.220
.275
.337

I've been attempting to figure out how to do the data analysis part of the lab for a while, and I was wondering if someone could show me a sample calculation for each on

[Teeny]

If someone could please help today, I'd appreciate it.
It's due Monday. I called my friends, everyone is lost.

[renge ishyo]

For data analysis question #2, use your line equation obtained from part II to find the equilibrium concentrations of [FeSCN²⁺]. Just plug in your absorption values obtained for each of the test tubes in part III into your line equation, solve for [FeSCN²⁺], and record the concentrations in the table provided.

For data analysis question #3, start by multiplying your answer from question #2, the [FeSCN²⁺] for say, test tube 1, by the total volume of [FeSCN²⁺] (which is 10 mL, but you probably need to use 1.0x10^-2L in your calculation so that the units come out right) to get moles of FeSCN²⁺. Next, calculate the moles that you started with of Fe³⁺ and SCN^- by using the table for mixing given way back on page 5 for the instructions on part III (step #12). Here is an example of how to get the starting moles for Fe³⁺ for test tube #1:

(.0020 mol/L Fe³⁺)(3.00x10^-3L) = 6.0x10^-6 mol Fe³⁺

Next, use the following equation to calculate the final moles of both Fe³⁺ and SCN^-:

Fe³⁺ + SCN^-   FeSCN²⁺

final moles Fe³⁺ = starting mol Fe³⁺ - mol FeSCN²⁺

final moles SCN^- = starting mol SCN^- - mol FeSCN²⁺

Take your final moles of both Fe³⁺ and SCN^- and divide each by the total volume (1.00x10^-2L) in order to convert them to equilibrium concentrations of each. Report these concentrations in the table provided for each test tube.

data analysis question #4 is easy if you did parts II and III correctly. Use the following formula and just plug in your answers from the previous two questions into the places where they go. Repeat for each test tube:

K_eq = [FeSCN²⁺]/[Fe³⁺][SCN^-]

[Teeny]

Thank you so much! =)

However, I still need help with question 1. Since the equation is absorbance = 251.85 [FeSCN2+]. How am I suppose to determine what the concentration of SCN is? And how do i figure out the actual concentration of SCN?