Question

given the initial and final ph. how do you determine how much of a strong acid to add to water to obtain the final ph.

given

intial ph = 4

final ph = 7

volume of water = 10 liters

concentration of strong acid (HCL)= 3 moles/L

So how much HCl (in mL) do we have to add to water to obtain the final ph of 4

Answer 1

Since - pH = 4 (initial) , [H₃O⁺] = 10^-4 M

    For pH = 7 (final) , [H₃O⁺] = 10^-7 M, volume of water = 10 L

Concentration of strong acid = 3 M

Therefore -

The volume of water that can be added to make intial quantity , V₁ = (10^-4 M)(10 L) / (3 M)

                                                                                                = 3.33*10^-4 L = 0.33 mL

For V₂ = (10^-7 M)(10 L) / (3 M)

          = 3.33*10^-7 L