On the strength of hydrofluoric acid
When it comes to acids in the world, it is often divided into strengths and weaknesses. As for hydrofluoric acid ($HF $), everyone's opinion is quite controversial.

Or hydrofluoric acid is a strong acid. Strong acids are almost completely ionized in water, releasing a large number of hydrogen ions ($H ^ + $), which are acidic and violent, can erode everything, and have extraordinary power. Common strong acids, such as hydrochloric acid ($HCl $), sulfuric acid ($H_2SO_4 $), and nitric acid ($HNO_3 $), are completely ionized in aqueous solutions, and hydrogen ions are free at will, showing strong acid properties. If hydrofluoric acid is a strong acid, the same should be true. The degree of ionization in water is extremely high, so that the solution is rich in hydrogen ions, showing strong acidity, and can quickly react violently with many substances.

However, hydrofluoric acid is also called non-strong acid. Because hydrofluoric acid is not completely ionized in water, there is an ionization equilibrium. $HF\ rightleftharpoons H ^ ++ F ^ - $, its ionization constant ($K_a $) is relatively small, indicating that hydrogen ions can not be free in large quantities without hindrance. And when hydrofluoric acid reacts with metals, its rate is slower than that of common strong acids. Take iron as an example, hydrochloric acid meets iron, bubbles rapidly, and hydrogen escapes, and the reaction is enthusiastic; while hydrofluoric acid reacts with iron, it is much slower. Furthermore, hydrofluoric acid can react uniquely with silicon dioxide ($SiO_2 $) to form silicon tetrafluoride ($SiF_4 $) and water. This reaction is its characteristic and implies that its acidic nature is different from that of ordinary strong acids.

Overall, although hydrofluoric acid is acidic and can react with many substances, it is difficult to simply determine that it is a strong acid because of its incomplete ionization in water and the difference in ionization degree and reactivity from traditional strong acids. When dialectical methods are used, comprehensive consideration of its characteristics can be used to obtain the solution of its true properties.