Concentration of Ions?

Question

Hi guys! Please help with the question!
A solution is prepared by dissolving 15.0 g NaOH in 150.0 mL of 0.250M nitric acid. Calculate the concentrations of all the ions present in the solution after the reaction has occured. Assume no volume change on addition of NaOH.

The equation would be: NaOH + HNO3 ---> NaNO3 +H2O

The way teacher explained was:
1) we find #moles of NaOH =..........=0.375 mol
2)find #moles HNO3 =...............=0.0375 mol
...but then she identifies concentration only for [OH], [NO3], [Na] ions....why not for [H] ion as well?
and to find the moles for OH^- she wrote:
OH^- = 0.375 mol - 0.0375 mol
why do we substract NaOH from HNO3 to find OH??

THANK YOU!!!!

Answer 1

Na OH + HNO3 --> NaNO3+H2O

so you see a mole of NaOH reacts with one mole HNO3
9If you calculate the molecular mass of NaOH you find 40 and 15g correspond to0.375mole of NaOH
1 liter of 0.250M correspond to 0.25 mole of HNO3 and 0.15l0L correspond to 0.0375mole of HNO3.

This means that NaOH is in a large excess. Only 0.0375mole of NaOH can react since there is not enough nitric acid.
So you see from the equation, you obtain 0.0375mole of
Na NO3 which dissociates completely and give
0.0375mole of Na+ and 0.0375 mole of NO3-
in ehe solution tere remains 0.375-0.0375=0.3375 mole of
Na OH which has not reacted. As NaOh isz completely dissociated you obtain 0.3375 moleof Na+ and 0.3375mole of OH-

lets see the end for NO3- you have 0.0375 mole
OH- 0.3375 mole
and Na+ =0.3375+0.0375= 0.375 mole of Na+

hoping it helps

Answer 2

The following ions are in solution at the end:

Na+, (NO3)-, H+ and OH-.

[Na+] is 0.375/0.15.

Some of the OH- ions have gone, so that is why she subtracted - to find how many were left. The NaOH was in excess, ie not all of it reacted.

[(NO3)-] is 0.25

There are some H+ ions present. [H+] = 10-14/[OH-]

Answer 3

Assuming answer is largely water, 3.5 liters weighs 3500 g. you've 5.fifty 5 x 10^-5 g of Pb so fraction via mass of Pb is 5.fifty 5*10-5/3500. to visit ppm, multiply via one million (a million*10^6) so fifty 5.5/3500 ppm = 0.0159 ppm.