The correct statements about the relative acid strengths of pairs of acids are as follows:
1. HCl is a stronger acid than H2S because Cl is more electronegative than S. This means that the chloride ion is better at stabilizing the negative charge that forms when the acid donates a proton.
2. H3PO4 is a stronger acid than HPO42- because it has more acidic hydrogen atoms. H3PO4 has three acidic hydrogen atoms, while HPO42- has only two. The more acidic hydrogen atoms, the stronger the acid.
3. HClO4 is a stronger acid than HClO3 because it has more oxygens around its central atom. The presence of more oxygens increases the polarity of the molecule, making it easier for the acid to donate a proton.
4. HClO4 is a stronger acid than HClO2 because it has more oxygens surrounding the central Cl atom. Again, the presence of more oxygens increases the acidity of the molecule.
5. H3PO4 is a stronger acid than H3AsO4 because P is more electronegative than As. The higher electronegativity of P makes it better at stabilizing the negative charge on the conjugate base, resulting in a stronger acid.
6. HBrO3 is a stronger acid than HBrO because it has more oxygens surrounding the central Br atom. As mentioned earlier, the presence of more oxygens increases the acidity of the molecule.
To summarize, the relative acid strengths of these pairs of acids are determined by factors such as electronegativity and the number of oxygens surrounding the central atom. Electronegativity affects the ability to stabilize the negative charge on the conjugate base, while the presence of more oxygens increases the acidity of the molecule.