Find the Molecular weight of unknown acid #5...

Mass of acid #5 = 1.200g
Volume (acid was mixed in) = 100ml (distilled water)
Conectration of NaOH = 0.989 M
Aliquot of acid titrated with NaOH = 25ml = 0.025 L
Average volume of NaOH from titration = 9.3ml = 0.0093L
Molar ratio of base to acid = 1:1 ( because it is monoprotic)
# of moles NaOH used? ____________
# of moles acid in 25ml solution ___________ mol
Gram-Molecular weight of unknown acid #5 ________________ g/mol

So the number of moles i got for NaOH was n= C*V = 0.0989 M * 0.0093 L = 0.00091977mol
And because its a monoprotic acid the # of moles of the acid is the same as the # of moles for the base.
So this is how I found the molar mass of the unknown acid #5....
n=m/M M = m/n M = 1.200g/0.00091977mol = 1304.67g/mol
My problem is that the molar mass seems REALLY off, I mean it’s huge! I did the experiment and followed the instructions carefully for this titration and yet the numbers are really messed up. I was hoping if someone could point out my mistakes and either fix up this titration calculation or at least let me know what I did wrong because I clearly have no idea what I am doing wrong.

First I note you SAY, in the problem, that you used 0.989 M NaOH but in the calculation you have 0.0989 M. I remember the first problem and the 0.0989 was what you used so I presume that is not the error. The error is that you did NOT use 1.2 g; you used 1.2 x (25/100) = 0.3 g and if you divide 0.3/moles I get something like 326 or so. Check me out on that. (Just divide that 1304.67 by 4).

To find the molar mass of the unknown acid #5, you have correctly determined the number of moles of NaOH used in the titration as 0.00091977 mol. Since the acid is monoprotic, the number of moles of acid in the 25 ml solution is also 0.00091977 mol.

However, there seems to be a mistake in your calculation of the molar mass. You divided the mass of the acid (1.200 g) by the number of moles (0.00091977 mol) to calculate the molar mass.

The correct calculation should be:
Molar mass (M) = mass (m) / number of moles (n)
M = 1.200 g / 0.00091977 mol = 1305.41 g/mol

So the correct molar mass of the unknown acid #5 is 1305.41 g/mol, which is close to the value you calculated.

It's important to note that experimental errors can occur during the titration process or in the measurement of masses and volumes, which could contribute to the discrepancy between the expected and calculated molar mass. It's always a good idea to double-check your measurements and calculations and repeat the experiment if necessary to ensure accuracy.