Phosphoric acid is a triprotic acid with the following pka values:

pka1=2.148, pka2=7.198, pka3=12.375

you wish to prepare 1.000 l of a 0.0500 m phosphate buffer at ph 7.540. to do this, you choose to mix the two salt forms involved in the second ionization, nah2po4 and na2hpo4, in a 1.000 l volumetric flask and add water to the mark. what mass of each salt will you add to the mixture?

mass nah2po4

mass na2hpo4

what other combination of phosphoric acid and/or its salts could be mixed to prepare this buffer? (check all that apply).

h3po4 and nah2po4

h3po4 and na2hpo4

h3po4 and na3hpo4

nah2po4 and na3po4

na2hpo4 and na3po4

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.

one negative thing it that it can kill water animals. another negative thing is it can cause the destruction of ecosystem. one way water pollution can be reduced is to conserve energy.