How can you find the pH if 75 grams of HCl (hydrochloric acid) is put in 5.0L of water?

I understand that I have to convert the grams to mol, and I have the molarity, but I don't know if the concentration is of hydrogen or hydroxide ions. Can anybody help me? Thanks!

1 Answer
May 11, 2018

Answer:

Well, let's see...I gets #pH=0.386#

Explanation:

We assume that hydrogen chloride undergoes complete protonolysis in aqueous solution...

#HCl(g) +H_2O(l) rarrH_3O^+ + Cl^-#

And so we calculate the concentration of #HCl# in the usual way...

#[HCl]="Moles of HCl"/"Volume of solution"#

We ASSUME (reasonably) that the volume of THE SOLUTION is #5.0*L#...it would be very close...

And so...#[HCl]=((75*g)/(36.46*g*mol^-1))/(5.0*L)=0.411*mol*L^-1#

And so it is #0.411*mol*L^-1# with respect to hydronium ions... which we represent as #H_3O^+# or #H^+#...

#pH=-log_10[H_3O^+]=-log_10(0.411)=-(-0.386)=+0.386#

The maximum concentration of #HCl# is approx. #10.6*mol*L^-1#...what is #pH# here...?