Stomach acid has a hydronium ion concentration of 1.2 x 10^-3 M. What is its pH?

1. Apply the definition: pH is minus the logarithm of the hydronium ion molarity. 2. Split the number: the logarithm of 1.2 x 10^-3 is log 1.2 plus log 10^-3. 3. Those parts are 0.08 and minus 3, giving minus 2.92 in total. 4. Changing the sign gives pH = 2.92. 5. Quoting 3.08 comes from subtracting the 0.08 instead of adding it. 6. Two significant figures in the concentration justify two decimal places in the pH. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.2 pH and pOH_