Question

P4O10(s) + 6 H2SO4(l) --> 4 H3PO4(aq) + 6 SO3(g)

Pure H2SO4(l) has a density of 1.84 g/mL. If 45.0 mL of H2SO4(l) reacts:

What mass of P4O10 reacts?

- it's given 45.0 mL of H2SO4 with the density of 1.84 g/mL, so the mass of H2SO4 is 45*1.84 = 82.8 (g) so converts to 0.845 moles of H2SO4
- the ratio between P4O10 and H2SO4 is 1 : 6, so the moles of P4O10 reacting is 0.141
so the mass of P4O10 reacts is 0.141*284 = 40.044 (g)

What volume of SO3(g) at STP is produced?

- the ratio between H2SO4 and SO3 is 1 : 1, so the moles of SO3 produced is 0.845
so the volume of P4O10 produced is 0.845*22.4 = 18.928 (L) in STP

A 200. mL sample of H3PO4 is titrated with 56.2 mL of 0.700M NaOH.
2 NaOH(s) + H3PO4(l) --> Na2HPO4(s) + 2H2O(l)

a) What is the molar concentration of H3PO4?

it's given 56.2 mL of 0.700M NaOH, so converts to 56.2/1000*0.7 = 0.04 moles of NaOH
- the ratio between NaOH and H3PO4 is 2 : 1, so the moles of H3PO4 needed is 0.02
- 0.02 moles H3PO4 in a 200 mL sample of H3PO4, that means the molar concentration of H3PO4 is 0.02/(200/1000) = 0.1(moles/L)

b) How many moles of Na2HPO4 are produced? (2 marks)

- the ratio between NaOH and Na2HPO4 is 2 : 1, so the moles of Na2HPO4 produced is 0.02

Answer 1

Looks good to me, except for 2B. Double check that one. The moles of H3PO4 are proportional to its conjugate base.

Answer 2

Nevermind. That one is correct as well.

Answer 3

Thank you !

Answer 4

H3PO4/H2SO4 problem is OK>
For M H3PO4 I get 0.098M
For mols Na2HPO4 I get 0.0196