acid/base... weak or strong... help please

[coolchix321]

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How do you determine if a molecule is a strong base or acid or weak acid or base...
How do you determine the stability?
Because F is more electronegative than Cl, but HF is a weaker acid than HCl....??
Thanks

 

[inaccensa]

How do you determine if a molecule is a strong base or acid or weak acid or base...
How do you determine the stability?
Because F is more electronegative than Cl, but HF is a weaker acid than HCl....??
Thanks

There are a no of criteria. First of all u should know the strong acids

HCl, HBr, HI, H2SO4, HNO3, HClO4

These are stong acids, since they completely dissociate. Moreover, the leaving group namely cloride, bromide and iodide are excellent leaving groups. It is sufficient to say that they are stabilized due to their large sizes. The large size makes them polarizable, ie-spread the negative charge. Fluoride ion is the smallest of the three and it is more electronegative. But I think the real reason why it doesn't form a strong acid is because fluoride ion is not as stable as the other 3 or it is a strong conjugate base. Hope this helps!!

 

[coolchix321]

so how do you determine if a molecule is a strong base or weak acid or base? How do you determine the stability?

 

[549]

Strong bases are group 1 hydroxides and oxides (like NaOH or Li2O...). Also Heavy group 2 hydroxides (Ba and down) and metal amides (like NaNH2). Weak acids and bases are anything not mentioned as strong.

My orgo teacher made us memorize common pKa values for many functional groups, and that usually helps me on questions where you have to compare acidities or basicities. Depending on how long you have, it may be worth studying.