Year 12s: what will be the first way you research your future options? >>

pH calculations help

Calculate the pH of the solution formed when:

a)20cm^₃of 0.10 mol dm^-3 HCL is added to 30cm^₃ of 0.04 mol dm^-3 NaOH

So I worked out which one is in excess. 0.002 Mol of HCL and 0.0012 Mol of NaOH = 0.0008 Mol of HCL left and the total volume is 0.050 cm^₃ so 0.0008/0.050=0.016 -LOG(0.016) = 1.80pH

but no idea how to do the next ones?

b) 100 cm³ of water is added to 25cm³ of 0.50 mol dm^-3 KOH
c) 15 cm³ of 0.50 mol dm^-3 H₂SO₄ is added to 100 cm³ of 0.75 mol dm^-3 KOH
d) 20cm³ of 0.15 mol dm^-3NaOH is added to 50 cm³ of 0.10 mol dm^-3 propanoic acid (K_a= 1.35x10^-5 )

Reply 1

Secret.

Original post by Loiks94

For b) do you know the formula to work out concentration of H+ from OH-?

Spoiler

For c) It is the same as the first question using HCl as it is a strong acid + strong base. BUT be careful as H2SO4 is diprotic (the concentration of H+ is double the concentration of the acid as there is H2SO4

For d) Work out moles and then whichever is in excess. If it is OH- then use the formula above. If it is HA (weak acid) then use the Ka formula