weak acid, strong base

[coolchix321]

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....
im confused

Thanks

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[Schemp]

You should just know a few common strong acids, like H2SO4, HCl, etc., and a few weak acids like acetic acid and ethanol. Same goes for bases. Anything beyond that should typically be mentioned in a passage. Knowing your solubility rules won't hurt either.

 

[DendWrite]

While electronegativity and bond polarity is one factor in determining acid strength, another is atomic radius and bond strength (http://en.wikipedia.org/wiki/Acid#Atomic_radius_and_bond_strength). Keep in mind that a stronger acid will release more protons (H+) into solution. In the case of HF versus HCl, while F is more electronegative than Cl, the bond in HCl is weaker, and this effect tends to predominate with the halogenic acids.

 

[Alwaysbehopeful]

Here are TPR's rules and I have found them to be 100% true thus far.

STRONG ACIDS (memorize)
H2SO4
HCL
HBr
HI
HCLO3, HCLO4
HNO3

Trend for acidity is increasing down and to the right. So across a period, increasing to the Right due to ELECTRONEGATIVITY. Down a group, it increases due to ATOMIC RADIUS.

STRONG BASES (memorize)
Group 1 Hydroxides (i.e. NaOH, KOH)
Group 2 Oxides (i.e. Li2O)
Some Group 2 hydroxides (Ba(OH)2, Sr(OH)2, Ca(OH)2)
- "Black scary cat"
Metal amides (i.e. NaNH2) ---- will be in Ochem too

Any other besides these are considered WEAK! So I just memorized these, they are not that hard. So far I haven't found these to be untrue. According to TPR, these are the ones you are required to memorize for the MCATs.

I hope that helped!