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Chemistry · Ch 3 — Ionic Equilibria

Acidity, basicity and neutrality of aqueous solutions

3.6.2

Acidity, basicity and neutrality of aqueous solutions

1. Neutral solution : For pure water or any aqueous neutral solution at 298 K

[H3O+]=[OH−]=1.0×10−7 M[\mathrm{H_3O^{+}}] = [\mathrm{OH^{-}}] = 1.0 \times 10^{-7}\ \mathrm{M}

Hence, pH=−log⁡10[H+]=−log⁡10[1×10−7]=7pH = -\log_{10}[\mathrm{H^{+}}] = -\log_{10}[1 \times 10^{-7}] = 7.

2. Acidic solution : In acidic solution, there is excess of H3O+\mathrm{H_3O^{+}} ions, or [H3O+]>[OH−][\mathrm{H_3O^{+}}] > [\mathrm{OH^{-}}]. Hence, [H3O+]>1×10−7[\mathrm{H_3O^{+}}] > 1 \times 10^{-7} and pH<7pH < 7.

3. Basic solution : In basic solution, the excess of OH−\mathrm{OH^{-}} ions are present, that is [H3O+]<[OH−][\mathrm{H_3O^{+}}] < [\mathrm{OH^{-}}], or [H3O+]<1.0×10−7[\mathrm{H_3O^{+}}] < 1.0 \times 10^{-7} with pH>7pH > 7.

Figure 3.1The pH scale from 0 to 14 drawn as a dual-row grey bar: the top row gives pH values 0 to 14 with Acidic (0-7), Neutral (7) and Basic (7-14) ranges arrowed above, and the aligned bottom row gives the matching hydronium-ion concentration from 1 down to 10 to the minus 14 mol per litre.
Fig. 3.1 — The pH scale from 0 to 14 drawn as a dual-row grey bar: the top row gives pH values 0 to 14 with Acidic (0-7), Neutral (7) and Basic (7-14) ranges arrowed above, and the aligned bottom row gives the matching hydronium-ion concentration from 1 down to 10 to the minus 14 mol per litre.

Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your textbook's own diagram.

What this figure shows. A horizontal grey scale bar carrying two aligned rows of numbers: the top row is the pH value (00 to 1414); the bottom row is the corresponding [H+][\mathrm{H^{+}}] in mol dm−3^{-3} (11, 10−110^{-1}, 10−210^{-2}, …\ldots, 10−1410^{-14}) -- each step of one pH unit is a tenfold change in hydronium-ion concentration. Above the bar, double-headed arrows mark the acidic range (00 to 77) and the basic range (77 to 1414), with the neutral po …

Note

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