Final answer:
The concentration of hydrofluoric acid (HF) is 0.0013 M in a solution with a pH of 2.90.
Step-by-step explanation:
To calculate the concentration of hydrofluoric acid (HF) in a solution with a pH of 2.90, we need to use the fact that pH is the negative logarithm of the hydrogen ion concentration ([H+]). In this case, the pH is 2.90, so we can find [H+] by taking the antilog of -2.90. Antilog(-2.90) = 0.0013. Since HF is a weak acid, we can assume that it is fully dissociated and the concentration of [H+] is equal to the concentration of HF. Therefore, the concentration of hydrofluoric acid is 0.0013 M.