NEED HELP ASAP PLS
CHEMISTRY
What is the percent of phosphorus by mass in phosphoric acid,
H3PO4? Use 1008 g/mol for the molar mass of hydrogen, 16.00
g/mol for the molar mass of oxygen, and 30.97 g/mol for the
molar mass of phosphorus.

31.60% phosphorus

Explanation:

To find the percent by mass, you first calculate the total mass and then the mass of phosphorus, and finally divide phosphorus mass by total.

Phosphorus mass: the molar mass of P is 30.97 g/mol, and since there's 1 mole of P, we just have 30.97 g.

Total mass: we add all the molar masses of the components together.

We have 3 moles of H, so we multiply 3 by 1.008 g/mol = 3.024 g H.

We already calculated the mass of phosphorus: 30.97 g P.

We have 4 moles of O, so we multiply 4 by 16.00 g/mol = 64.00 g O.

The total is then the sum: 3.024 + 30.97 + 64.00 = 97.994 g ≈ 97.99 g

Now, to find the percentage, we take 30.97 g P and divide by 97.99:

30.97/97.99 ≈ 0.3160 ⇒ 31.60% P

Thus, the answer is 31.60% phosphorus.

Hope this helps!

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.

c is the answer because when something is left after something evaporates that shows the chemical change.