In a 1.0× 10–6 m solution of hcl(aq) at 25 °c, identify the relative molar amounts of these species from most to least: h2o, hcl, cl-, oh-, h3o+

The relative molar amounts of these species from most to least is; H2O > H3O+ ≈  Cl- > OH- > HCl

We know that the equation of the reaction is represented as follows;

HCl(aq) + H2O(l) ⇄ H3O^+(aq) + OH^-(aq) + Cl^-(aq)

We know that water is present in large excess.

Also; [H3O^+] = [Cl^-]

Since it is an acid, the concentration of hydronium ions exceeds the concentration of hydroxide ions.

It then follows that the molar amounts of the species is;

H2O > H3O+ ≈  Cl- > OH- > HCl

HCl is least because the acid dissociates completely in water.

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[H₂O] > [H₃O⁺] ≳ [Cl⁻] > [OH⁻] > [HCl]

Explanation:

HCl + H₂O ⟶ H₃O⁺ + Cl⁻

HCl dissociates completely in solution.

[HCl] = 0 mol·L⁻¹

[H₃O⁺] = 1.0 × 10⁻⁶ mol·L⁻¹

[Cl⁻] = 1.0 × 10⁻⁶ mol·L⁻¹

[H₃O⁺] is slightly greater than [Cl⁻] because the autoionization of water also creates some hydronium ion.

1 L of water has a mass of 1000 g.

∴ [H₂O] = 55.49 mol·L⁻¹

∴ [H₂O] > [H₃O⁺] ≳ [Cl⁻] > [OH⁻] > [HCl]

   55.5       10⁻⁶        10⁻⁶     10⁻⁸        0

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