Question

"The higher the pH of the dilute nitric acid the longer it took for the gas syringe to fill with gas."

Why?

Answer 1

The higher the pH, the more basic (or less acidic) the solution is. I'm guessing the reaction you're talking about involves H+ ions as a reactant (e.g. which ultimately form H2 gas), so the less of them you have around, the longer the reaction will take.