Final answer:
To rank compounds by acidity or basicity, one must consider their ability to donate or accept hydrogen ions, respectively. Acid strength increases with the ability to stabilize the conjugate base, while basicity increases with the willingness to accept a proton. Factors such as electronegativity and atom size significantly influence these properties.
Step-by-step explanation:
The question at hand involves the comparison of the acidity and basicity of various compounds. Acidity relates to the tendency of a compound to donate a hydrogen ion (proton), while basicity pertains to the ability to accept a hydrogen ion.
For ranking acidity, you can compare the ability of compounds to donate protons. For example, among the hydrogen halides (HCl, HBr, HI), HI is the most acidic because iodine is larger and can better stabilize the negative charge on the resulting iodide ion compared to chlorine or bromine. For HF, H2O, NH3, and CH4, HF is the most acidic as it can donate a proton to form the relatively stable fluoride ion. Factors like electronegativity and the stability of the conjugate base play a key role in determining acidity.
For basicity, you should consider the ability to accept protons. For instance, OH- is a stronger base than H2O because OH- is more willing to accept a proton to form H2O. Amongst the hypo-halite ions (HOCl, HOBr, HOI), HOI is the least acidic because iodine is less electronegative and less inclined to hold onto the proton. Basicity can be influenced by the electronegativity of the atom bound to the oxygen and the overall stability of the molecule.
Regarding compound pairs such as NH3 vs H2O, H2O is more acidic as it can more readily donate a proton to form OH-, while NH3 is a weaker acid but a stronger base as it prefers to accept a proton.