Question

Which molecule will form a solution with a very low pH?

H3PO4
H2O
NaOH
KOH

Answer 1

The correct answer is A: H3PO4

Answer 2

Answer: Option (a) is the correct answer.

Step-by-step explanation:

A solution which has more number of hydrogen ions will be acidic in nature and its pH will be less than 7. Whereas a solution which has more number of hydroxide ions will be basic in nature and thus, its pH will be greater than 7.

Also, pH =
`-log (1)/(H^(+))`

Therefore, a low pH means pH will be very less than 7.

The given molecules will dissociate as follows.

`H_(3)PO_(4) \rightleftharpoons 3H^(+) + PO^(3-)_(4)`

`H_(2)O` being a neutral molecule will not dissociate and pH of water is 7. Hence, it is a neutral molecule.

`NaOH \rightleftharpoons Na^(+) + OH^(-)`

`KOH \rightleftharpoons K^(+) + OH^(-)`

So, we can see that
`H_(3)PO_(4)` gives maximum number of hydrogen ions. Therefore, we can conclude that molecule of
`H_(3)PO_(4)` will form a solution with a very low pH.