Question

What are the products of the following reaction? `2Al(s) + 6H^+ (aq) ->`

Answer 1

Aluminium cations and hydrogen gas.

Explanation:

You were given the reactants in the net ionic equation that describes the reaction between aluminium metal, `"Al"`, and hydrochloric acid, `"HCl"`.

Hydrochloric acid is a strong acid, which means that it dissociates completely in aqueous solution to form hydrogen ions, `"H"^(+)`, which you'll very often see referred to hydronium cations, `"H"_3"O"^(+)`, and chloride anions, `"Cl"^(-)`.

`"HCl"_ ((aq)) -> "H"_ ((aq))^(+) + "Cl"_ ((aq))^(-)`

You can thus rewrite the equation as

`2"Al"_ ((s)) + 6"H"_ ((aq))^(+) + 6"Cl"_ ((aq))^(-) -> ?`

Remember, the stoichiometric coefficient of the hydrogen ions must also be distributed to the chloride anions, since

`6"HCl"_ ((aq)) -> 6"H"_ ((aq))^(+) + 6"Cl"_((aq))^(-)`

Now, when aluminium reacts with hydrochloric acid, it gets oxidized to aluminium cations, `"Al"^(3+)`. At the same time, the hydrogen ions get reduced to hydrogen gas, `"H"_2`.

`2"Al"_ ((s)) + 6"H"_ ((aq))^(+) + color(red)(cancel(color(black)(6"Cl"_ ((aq))^(-)))) -> "Al"_ ((aq))^(3+) + color(red)(cancel(color(black)(6"Cl"_ ((aq))^(-)))) + "H"_ (2(g)) uarr`

As you can see ,the chloride anions are spectator ions, which is why the initial equation didn't include them

`2"Al"_ ((s)) + 6"H"_ ((aq))^(+) -> "Al"_ ((aq))^(3+) + "H"_ (2(g)) uarr`

Now all you have to do is balance the aluminium and hydrogen atoms

`color(green)(|bar(ul(color(white)(a/a)color(black)(2"Al"_ ((s)) + 6"H"_ ((aq))^(+) -> 2"Al"_ ((aq))^(3+) + 3"H"_ (2(g)) uarr)color(white)(a/a)|)))`

The products of the reaction will thus be aqueous aluminium cations, `"Al"^(3+)`, and hydrogen gas, `"H"_2`.

If you want, you can add in the chloride anions to get

`2"Al"_ ((s)) + 6"H"_ ((aq))^(+) + 6"Cl"_ ((aq))^(-) -> 2"Al"_ ((aq))^(3+) + 6"Cl"_ ((aq))^(-) + 3"H"_ (2(g)) uarr`

This is equivalent to

`2"Al"_ ((s)) + 6"HCl"_ ((aq)) -> 2"AlCl"_ (3(aq)) + 3"H"_ (2(g)) uarr`

The single replacement reaction reaction between aluminium metal and hydrochloric acid produces aqueous aluminium chloride and hydrogen gas.