Formula to solve a complex chemistry equation

I am working with the following equation

V_b= V_a [(C_a/(1+([H^+])⁄K_a ) - [H^+] + K_w/([H^+]))/(C_b/(1+K_w⁄([H^+]K_b )) + [H^+ ] - K_w/([H^+]))]

C_a, C_b, K_a, K_b, K_w and V_a are all constants or have known values. I want to set up a range of values for V_b from which to calculate [H^+ ]. This is not a trivial problem and I need to know how the calculation can be performed.

Maybe using the Solver add-in (perhaps not) or by writing code in VBA. If the latter I would need help in writing the code because I am not a mathematician.

Expected result for C_a = 0.1, C_b = 0.1, K_a = 1.74E-5, K_b = 0.63, K_w = 1.0E-14, V_a = 25, [H^+] = 1.95E-9 is V_b = 25 (or close to)

Thanks for that Bernie but I am not sure how to use that to fill in a series as in the attachment

Sorry for the confusion - I want to calculate V_b from given values of pH (or [H^+ ]). In other words I know what pH I want to achieve from that I can get [H^+ ] because pH is simply -log([H^+ ]) and I need to calculate the V_b which will give me the desired pH.

I will need to be able to set different values for C_a, C_b, K_a, K_b and V_a. K_w is always constant. Thanks for your patience!

That's absolutely great, many thanks. Now I would like to be able to do the reverse.
In other words, calculate [H^+ ] for given values of V_b

Many thanks for that Bernie - it's a great starting point for me take off from. I'd like to clarify a couple of points in the FindSolution2 code though.

For Each rngC In Range(Range("F10"), Cells(Rows.Count, "F").End(xlUp))
rngC.Offset(0, 3).GoalSeek Goal:=rngC.Value, ChangingCell:=rngC.Offset(0, 1)
Next rngC

1. Am I right in thinking that the code in red selects each cell from F10 down to the last non-empty cell and that's the purpose of .End(xlUp)?

2. My understanding of the way GoalSeek works is this: Change the [H+] values in column G, perform the calculation in column I and repeat until the value in column F is achieved. Is that correct?

3. I don't understand how clicking the button invokes the FindSolution2 code - there doesn't seem to be any code for the button (like Button_Click for example) that would call the FindSolution2 code.

Lastly, it goes almost without saying, I am very grateful for all your help. I do appreciate the time and effort you have spent. If the rules allow, I would like to make a small contribution to your favourite charity as a token of my appreciation. Please let me know if I can do that.