Question

give answer in about 40-50 words .why these order in acidic strength give reason propanoic acid<ethanoic acid<2-chloroethanoic acid<2-fluoroethanoic acid<dichloroethanoic.

Answer 1

See, here you have to look at two things, first, when alkyl group keeps increasing, electron pushing effect increases, more tha alkyl group, more the electron pushing, and more stronger the carbon which is bonded with oxygen (in COOH) which thus makes it harder to release H+ ion, decreasing the acidity. That's why, propanoic acid is weaker than ethanoic acid and so on.

But when it comes to halogen attached acids, we should know that halogens have the property of "pulling electrons" rather than pushing, because halogens being electronegative. So the pull electrons from the carbon, making the carbon weak, making it easier for the H+ ion to release. That's why chloroethanoic acid is weaker than floroethanoic acid and so on.

Remember, more it is easy to release H+ ions, more it is acidic.

Hope this helps.