Question

What is a substance with a pH of 4 called?

Answer 1

Acidic

Explanation:

pH is just a fancy scale for representing the concentration of `H_3O^+` (hydronium) ions in the solution. To find the concentration of hydronium ions, you just take `10^(-pH)`, which simplifies to `1/10^(pH)`, if you prefer seeing it that way.

As you can see, therefore, substances with smaller pH values will have a `color(red)("larger hydronium ion concentration.")` and we call these `color(red)("acidic")`

Similarly, substances with larger pH values will have `color(blue)("lower hydronium ion concentrations")`, and we call these `color(blue)("basic")`

Our baseline is that a `color(green)("pH of 7 is considered neutral")`. Anything above is basic, anything lower is acidic.

So, bearing all that in mind, a pH of 4 would be considered `color(red)("acidic")`

Hope that helps :)