CHEMISTRY COMMUNITY

I haven't taken Chem 14A in a long time, so I don't remember how to figure out if an acid/base is strong or weak. Can someone please explain how you could determine if an acid or base is strong or weak without being given the chemical equation?

Also, in class,the Professor did an example where we had to find the moralities of H3O+ and OH- if there was .0030 mol/L of Ba(OH)2. How would you know that Ba(OH) is a strong base or weak base based on this information only and how would I know how to write the chemical equation for this as well?

Thanks!

you basically have to memorize them. Feel free to correct me but I think the list is (there may be a few more bases but i am not 100% sure)
Acids: HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4
Bases: LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

We had to memorize our Strong Acids and Bases which are
HCl - hydrochloric acid
HNO3 - nitric acid
H2SO4 - sulfuric acid (HSO4- is a weak acid)
HBr - hydrobromic acid
HI - hydroiodic acid
HClO4 - perchloric acid
HClO3 - chloric acid.

Potassium hydroxide (KOH)
Sodium hydroxide (NaOH)
Barium hydroxide (Ba(OH)2)
Caesium hydroxide (CsOH)
Strontium hydroxide (Sr(OH)2)
Calcium hydroxide (Ca(OH)2)
Lithium hydroxide (LiOH)
Rubidium hydroxide (RbOH)

Any other acid/base is weak.

A good rule of thumb for strong bases is that the cation of the base is typically in the first or second group within the periodic table.

While it is good to memorize specifically which are acids and bases, there are a couple of indicators for just figuring it out yourself
Strong acids: Generally a H+ ion with a nonmetal with a large radius, such as HCl or HBr, oxyacids (acids with oxygen) with more oxygen (for example, HNO3 is a stronger acid than HNO2), elements with a strong charge (+3 or more such as Al3+)

Weak acids: H+ with a nonmetal with a small radius, such as HF

Strong bases usually have H-, OH- or O-2

Note that the conjugate bases of strong acids (which is Cl out of H, or Br- out of H) are neutral, as are alkaline metals such as Na+.

Then is there no way to determine whether an acid or base is strong by just looking at the compound itself? It's just memorization?

From looking at a reaction, if it dissociates fully and forms a salt and water then that would be another way to recognize a strong acid or a strong base.

You can also tell from the pKa of the reaction. The smaller the pKa value, the stronger the acid.