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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