When an acid dissolves in water, what ion does water form?

1 Answer
anor277
Aug 27, 2017

Well, we conceive it to be the "hydronium ion......."

Explanation:

Water is conceived to undergo an autoprotolysis reaction as shown.....

2H_2OrightleftharpoonsH_3O^+ + HO^-, where ..........

K_w=[H_3O^+][HO^-]=10^-14 under standard conditions.

When an acid, say HX, is dissolved in water, we conceive it to INCREASE the concentration of the characteristic cation, H_3O^+, and accordingly reduce concentrations of the characteristic anion, HO^-, so that the autoprotolysis equilibrium is maintained.

And a base likewise increases concentrations of the characteristic anion, HO^-.

We can quantify the acid-base equilibrium in water under standard conditions by the equation......

2H_2OrightleftharpoonsH_3O^+ + HO^-, where.....

K_w=10^-14=[H_3O^+][HO^-]

And taking -log_10 of both sides.....

-log_10K_w=-log_(10)10^-14=-log_10[H_3O^+]-log_10[HO^-]

And thus 14=underbrace(-log_10[H_3O^+])_"pH"+underbrace(-log_10[HO^-])_"pOH"

And thus our working equation.....14=pH+pOH.

See here for practical issues with respect to the uses of acids in water.

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