A weak acid, exactly

A weak acid has $K_a = 6.3 \times 10^{-5}$. You will find its hydronium concentration by the shortcut and by the exact quadratic, the share that ionises, and the pH.

The idea. The shortcut is $\sqrt{K_a C}$. The exact value is the positive root of $x^2 + K_a x - K_a C = 0$.

Your tasks.

1. Set short to the shortcut value of $[\text{H}_3\text{O}^+]$, in mol/L.
2. Set exact to the positive root of the quadratic.
3. Set share to the per cent of the acid that ionises, from exact.
4. Set ph to the pH, from exact.