Down group 17 the H–X bond becomes longer and weaker, so the proton is released more easily. This bond-strength effect outweighs the fall in electronegativity, making HI the strongest.
Question 2 True / False
HF is a weak acid in water even though fluorine is the most electronegative element.
TTrue
FFalse
Answer: True
The H–F bond is very strong, and this outweighs its high polarity. HF has a Ka of roughly 10⁻³ to 10⁻⁴, while HCl, HBr and HI are strong acids.
Question 3 Short Answer
Rank HOCl, HClO₂, HClO₃ and HClO₄ from weakest to strongest acid, and explain the trend.
Think about your answer, then reveal below.
Model answer: HOCl < HClO₂ < HClO₃ < HClO₄. Each extra oxygen on chlorine withdraws electron density from the O–H bond and lets the negative charge of the conjugate base spread over more oxygen atoms.
The acidic proton is on an O–H group in each acid. More terminal oxygens make the O–H bond more polar and stabilize the anion by delocalization, so Ka rises sharply across the series.
Question 4 Multiple Choice
Among HOCl, HOBr and HOI, which is the strongest acid?
AHOCl
BHOBr
CHOI
DAll are equal
When the structure is the same, the more electronegative central atom pulls more electron density away from the O–H bond. Chlorine is the most electronegative of the three, so HOCl is the strongest.