Posted by Anonymous on .
select from the following the most appropriate concentration for NaOH to titrate a sample that contains 250mg of aspirin:
a. 0.01 M
b. 0.10 M
c. 1.0 M
and explain why you chose it.
250 mg aspirin = 0.250/molar mass.
mols aspirin = mols NaOH required.
Therefore, M = mols NaOH/L NaOH and I can't answer this question without knowing the size buret you will use.
In fact I would not want to use any of them.
I was always taught that if we used a 50 mL buret that we want to use about 40 mL to titrate a sample.
0.00139/0.04L = about 0.035M and that isn't one of the answers. Here is what I would do.
Calculate the volume each of the answers would give you and make a choice from that.
M = mols/L or L = mols/M
The first one gives 0.00139/0.01 = 0.139 or 139 mL and that means more than one 50 mL buret of NaOH. You never want to use more than one buret of stuff.
Next is 0.00139/0.1 = 0.0139 or about 14 mL. Frankly I wouldn't choose this one because this increases the error when small volumes are used; however, this probably is the best choice of the three.
The final one is 0.00139/1 = 0.00139 L or 1.39 mL which is FAR FAR too small. .I suspect you are to choose the middle one.
You might ask what I would do. I would use about 3x the sample of 750 mg which gives 0.750/180 = about 0.0042 mol and
0.0042 mols/0.01M = 0.042 L or about 42 mL.