If the pH of a solution increases by 4 (from 4 to 8), how much does the hydrogen ion concentration change? Does the change make the solution more acidic or more basic?
H+(conc) = 10^-pH
So, in the first case, H+ = 10^-4
in the second case, the concentration of H+ = 10^-8
Subtract these two to find the difference, or divide the two to find a ratio expressing the change.
A pH below 7 is acidic, a pH above 7 is basic, so increasing pH means the solution is becoming more basic; decreasing pH means the solution is becoming more acidic
pH went from acidic to basic