First, we must know that the hydronium ion is formed when a water molecule accepts a hydrogen ion. Therefore, the hydronium ion concentration is equivalent to the hydrogen ion concentration. Furthermore, the equation relating pH and hydrogen ion concentration is:
pH = -log[H+]
4.33 = -log[H+]
[H+] = 4.68 x 10⁻⁵ M
The concentration of hydronium ions is 4.68 x 10⁻⁵ M