Rank these acids from weakest to strongest: H2C2O4, HCO3-, H2PO4-, HCOOH.

To rank acids from weakest to strongest, we need to consider their acid dissociation constants (Ka) or acidity constants. The higher the Ka value, the stronger the acid.

1. H2C2O4 (oxalic acid): To determine the strength of oxalic acid, we need to look up its Ka value. However, oxalic acid is a diprotic acid, meaning it can donate two protons. In this case, it dissociates in two steps:

H2C2O4 ⇌ H+ + HC2O4- (Ka1)
HC2O4- ⇌ H+ + C2O4 2- (Ka2)

Since we don't have the specific Ka values, we cannot determine the exact strength of oxalic acid. However, it is generally considered a weak acid.

2. HCO3- (bicarbonate ion): Bicarbonate is also a weak acid. When dissolved in water, it can act as both an acid and a base:

HCO3- ⇌ H+ + CO3 2- (Ka)

The Ka value for bicarbonate is relatively small, indicating its weakness as an acid.

3. H2PO4- (dihydrogen phosphate): Dihydrogen phosphate is a slightly stronger acid compared to oxalic acid and bicarbonate. Its acid dissociation is as follows:

H2PO4- ⇌ H+ + HPO4 2- (Ka)

The Ka value of H2PO4- is higher than that of oxalic acid and bicarbonate, suggesting greater acidity.

4. HCOOH (formic acid): Formic acid is generally considered a stronger acid compared to the previously mentioned acids. Its acid dissociation is:

HCOOH ⇌ H+ + HCOO- (Ka)

The Ka value for formic acid is larger than those of oxalic acid, bicarbonate, and dihydrogen phosphate, indicating its stronger acidity.

Therefore, from weakest to strongest acid, we have H2C2O4 (oxalic acid) < HCO3- (bicarbonate ion) < H2PO4- (dihydrogen phosphate) < HCOOH (formic acid).