Anhydrous HF is a covalent compound and a weak acid, so it does not provide enough F⁻ ions to dissolve AlF3. However, KF is an ionic compound that completely dissociates to provide a high concentration of F⁻ ions. In the presence of KF, AlF3 acts as a Lewis acid and accepts these F⁻ ions to form the soluble coordination complex, potassium hexafluoroaluminate(III). The chemical equation for this reaction is: AlF3 + 3KF → K3[AlF6].