Strong acids

[Temper888]

---

Members do not see this ad.

Hey Guys,

What are strong acids? EK says they are seven:HCL, HBR, HI, H2S04, HN03,HCL04, and HCL03. However, BR says HCL03 is a weak acid. So, exactly what are strong acids? I am a little confused?

 

[MedPR]

Hey Guys,

What are strong acids? EK says they are seven:HCL, HBR, HI, H2S04, HN03,HCL04, and HCL03. However, BR says HCL03 is a weak acid. So, exactly what are strong acids? I am a little confused?

Strong acids are acids that dissociate completely in water.

HClO3 is a strong acid. Are you sure BR isn't talking about HClO?

 

[MT Headed]

By the laws of thermodynamics, a stronger acid and stronger base will react to form a weaker acid and a weaker base:
SA+SB-->WA+WB
note that stronger and weaker here are relative terms. WB is the conjugate base of the SA, and WA is the conjugate acid of the SB.

If the SA is strong enough, the SB can be water itself, and the WA would be the hydronium ion:
Strong Acid + H2O --> ConjBase + H3O+
That is the exact definition of a strong acid. The Ka of the acid must be larger than the Ka of the hydronium ion, or equivalently, the pKa of the acid must be less than the pKa of the hydronium ion (which is -1.74).

By this true definition, HClO3 with a pKa of -1 is not quite a strong acid. In fact, nitric acid with a pKa of -1.64 isn't either. That's right, at absurdly large concentrations of NO3-, the hydronium ion will donate its proton back to nitrate ion. But for the purposes of experimental laboratory chemistry, nitric acid solutions are so diluted that it does dissociate 100% like a strong acid.

Now that you know the exact definition of strong acids, as requested, for the purposes of the MCAT just use the 7 ones listed by EK and you will be fine.

 

[Temper888]

MedPR, Yes BR says in section IV(Acids and Bases), passage I, answer explanation for Q#4 "HCl03 is a weak acid". Page #281

I will just go with the EK.Thanks Guys.