# Chemistry

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Can you check if this is correct please?

a) How many moles of sodium hydroxide are there in 19.00 cm3 of 0.100 mol dm3?

b) How many moles of hydrochloric acid are, there in 25.00 cm3 of the acid solution?

c) How many moles of hydrochloric acid are, therefore in 1000cm3 of solution?
I did 0.0019 x 1000/25.00

d) What is the concentration of the hydrochloric acid solution?

I am stuck on this though:
The concentration of hydrogen ions in a 0.1 mol dm3 solution of phosphoric acid, H3PO4?
I would be able to do it if I knew the correct equation that = H3PO4 but I can't work it out.

If any of these are wrong can you please explain how they should be done thank you :)

• Chemistry -

a is right.
b--What acid solution? If this is a titration the answer is ok.
c--If this is NaOH titrated with HCl both c and d are correct.
For the last (un-lettered) question you have, H3PO4 is a triprotic acid. k1 = about 10^-3, k2 = about 10^-8 and k3 = about 10^-13.
So you set up an ICE chart and calculate the concn H^+.
............H3PO4 ==>H^+ + H2PO4^-
initial.....0.1.......0......0
change......-x........x.......x
equil......0.1-x......x........x

Essentially you ignore k2 and k3 since they are so much smaller than k1.
k1 = (H^+)(H2PO4^-)/(H3PO4)
Look up k1, subtitute the ICE data into the k1 expression and solve for H^+ = x.

• Chemistry -

Thank you. I know, the question was very long so I tried to shorten it for this but left out some details sorry!