Homework Help: chemistry

Posted by nicole on Monday, October 25, 2010 at 5:25pm.

i am calculating an unknown acid for both monoprotic and diprotic assumptions. I calculated the monoprotic by multiplying the M NaOH by the liters of NaOH used to titrate. 0.0984M x 0.02396= 0.00236. I then take the unknown sample weight and divide it by the previous number to get the g/mol. so 0.177 g/0.002356= 75.13 g.mol? is this correct for monoprotic? and for diprotic do i just multiply the NaOH answer by 2 and take the unknown sample and divide it by the new NaOH amount?

chemistry - DrBob222, Monday, October 25, 2010 at 5:35pm
I don't know if that M is to 3 s.f. or if you had another number after the 4. At any rate, I calculated 75.07 for the molar mass which would round to 75.1 to three s.f. For a diprotic, you do it this way.
H2A + 2NaOH ==> Na2A + 2H2O
moles NaOH = M x L
moles H2A = 1/2 moles NaOH
Then molar mass = grams/moles H2A.
chemistry - nicole, Monday, October 25, 2010 at 5:42pm
thank you so much. that helps a lot!

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