Question

Which equation represents the reaction of a weak acid with water?

A.
HCl + H2O H3O+ + Cl-
B.
HCO3– + H2O H2CO3 + OH–
C.
H2O H + + OH-
D.
HCOOH + H2O H3O+ + HCOO-

Answer 1

Acid is anything which will give H+ to other species.

Have a look at the equations given.

In A) HCl changes to Cl- by giving its H+ to H2O. So HCl is an acid.

In B) HCO3- changes to H2CO3^2- by accepting H+. It did Not give its H+ rather it takes from other species. So it is not an acid at all.

In C) H2O is just breaking to H+ and OH-. It is not giving H+ to other species. So it is also not an acid in this reaction.

In D) HCOOH is giving its H+ to H2O. So it is also an acid.

So out of all reactions with water. The only two species are acting as acid with water namely HCl and HCOOH.

Out of these two HCl is very strong acid but HCOOH is a weak acid.

So the answer is D

Answer 2

Answer: The correct answer is Option D.

Step-by-step explanation:

Weak acid is defined as the acid which does not completely dissociates into its ion when dissolved in water.

For the given options:

Option A:
`HCl+H_2O\rightarrow H_3O^++Cl^-`

HCl is a strong acid because it completely looses its proton when dissolved in water.

Option B:
`HCO_3^-+H_2O\rightarrow H_2CO_3+OH^-`

Hydrogen carbonate ion is a base because it is easily accepting a proton from water.

Option C:
`H_2O\rightarrow H^++OH^-`

The above equation represents the ionization of water.

Option D:
`HCOOH+H_2O\rightarrow H_3O^++HCOO^-`

Formic acid is considered as a weak acid because it does not completely dissociates into its ions when dissolved in water.

From the above information, the correct answer is Option D.