Question

the chemical formulae of some acids are listed in the first column of the table below, and in the second column it says whether each acid is strong or weak
complete the table. list the chemical formula of each species present at concentrations greater than about 10^-6 mol/l when about a tenth of a mole of the acid
is dissolved in a liter of water.
acid
strong or
weak?
species present at 10^-6 mol/l or greater
when dissolved in water
hbro_4
strong

hbr
strong

h_2s
weak

h_2co_3
weak

Explanation:

Step1: Analyze strong acid \(HBrO_4\)

Strong acids dissociate completely in water. The dissociation reaction of \(HBrO_4\) is \(HBrO_4(aq)
ightarrow H^{+}(aq)+BrO_{4}^{-}(aq)\). So the species present are \(H^{+}, BrO_{4}^{-}\).

Step2: Analyze strong acid \(HBr\)

The dissociation reaction of \(HBr\) (a strong acid) is \(HBr(aq)
ightarrow H^{+}(aq)+Br^{-}(aq)\). So the species present are \(H^{+}, Br^{-}\).

Step3: Analyze weak acid \(H_2S\)

Weak acids dissociate partially. The first - step dissociation of \(H_2S\) (the dominant dissociation as \(K_{a1}\gg K_{a2}\)) is \(H_2S(aq)
ightleftharpoons H^{+}(aq)+HS^{-}(aq)\). Also, water auto - ionizes \(H_2O(l)
ightleftharpoons H^{+}(aq)+OH^{-}(aq)\), but \(H_2S\) is the main source of \(H^{+}\) (since \(H_2S\) is dissolved in water and its concentration is relatively high). So the species present are \(H_2S, H^{+}, HS^{-}\).

Step4: Analyze weak acid \(H_2CO_3\)

For weak acid \(H_2CO_3\), the first - step dissociation \(H_2CO_3(aq)
ightleftharpoons H^{+}(aq)+HCO_{3}^{-}(aq)\) (dominant as \(K_{a1}\gg K_{a2}\)). Also, \(H_2CO_3\) itself is present (as it is a weak acid and does not dissociate completely). So the species present are \(H_2CO_3, H^{+}, HCO_{3}^{-}\).

Answer:

acid	strong or weak?	species present at \(10^{-6}\space mol/L\) or greater when dissolved in water
\(HBr\)	strong	\(H^{+}, Br^{-}\)
\(H_2S\)	weak	\(H_2S, H^{+}, HS^{-}\)
\(H_2CO_3\)	weak	\(H_2CO_3, H^{+}, HCO_{3}^{-}\)