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?

Question

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?

Answer 1

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.

Answer 2

thank you so much. that helps a lot!

Answer 3

To confirm if your calculations for the monoprotic assumption are correct, I'll break down your steps.

Step 1: Calculate the moles of NaOH used for titration.
You multiplied the concentration of NaOH (0.0984 M) by the volume of NaOH used (0.02396 L). Thus, 0.0984 M x 0.02396 L = 0.002356 moles NaOH.

Step 2: Calculate the molar mass of the unknown acid.
You divided the mass of the unknown sample (0.177 g) by the moles of NaOH obtained in Step 1. So, 0.177 g / 0.002356 moles = 75.13 g/mol.

Therefore, your calculated molar mass for the monoprotic assumption is indeed 75.13 g/mol.

Now, for the diprotic assumption, here's what you need to do:

Step 1: Multiply the moles of NaOH obtained in Step 1 by 2 since each mole of diprotic acid reacts with two moles of NaOH.
0.002356 moles NaOH x 2 = 0.004712 moles NaOH.

Step 2: Calculate the molar mass of the unknown acid.
Divide the mass of the unknown sample (0.177 g) by the moles of NaOH obtained in Step 1 (0.004712 moles): 0.177 g / 0.004712 moles = 37.58 g/mol.

Therefore, your calculated molar mass for the diprotic assumption is 37.58 g/mol.

In summary:
- For the monoprotic assumption, your molar mass calculation is correct at 75.13 g/mol.
- For the diprotic assumption, your molar mass calculation should be 37.58 g/mol.

Remember, these calculations assume that the acid is either monoprotic or diprotic, and the results may vary depending on the actual nature of the acid. It's always good to double-check your calculations and ensure accurate lab procedures.