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How To Find Hydrogen Ion Concentration
On the Method of Determining the Concentration of Hydrogen Ions
If you want to know the concentration of hydrogen ions in a solution, there are various methods, which need to be reviewed in detail and selected according to different situations.
If the solution is a strong acid, the strong acid is almost completely ionized in water. For example, hydrochloric acid (HCl), one mole of hydrogen ions (H 🥰) is released per mole of HCl dissolved in water. Let the amount and concentration of the substance in the HCl solution be\ (c\) \ (mol/L\), then the concentration of hydrogen ions in the solution is\ ([H 🥰] = c\) \ (mol/L\). This is a clear reason, which is due to the ionization characteristics of strong acids.
As for the strong base solution, although mainly hydroxide ions (OH), according to the ionic product constant of water\ (K_w = [H] [OH]\), at room temperature\ (K_w = 1.0 × 10 ⁻¹⁴\) 。 If the concentration of hydroxide ions in the strong base solution is known\ ([OH]\), the hydrogen ion concentration\ ([H] =\ frac {K_w} {[OH ⁻]}\) 。 For example, in sodium hydroxide (NaOH) solution, if\ ([OH] = 0.1\) \ (mol/L\) is determined, then\ ([H 🥰] =\ frac {1.0 × 10 ◕} {0.1} = 1.0 × 10 ⁻¹³\) \( mol/L\).
The case of weak acids is more complicated. Weak acids are only partially ionized, such as acetic acid (CH 🥰 COOH), and their ionization equilibrium constant\ (K_a =\ frac {[CH 🥰 COO] [H 🥰]} {[CH 🥰 COOH]}\). Let the initial concentration of acetic acid be\ (c\) \ (mol/L\), and when the ionization equilibrium is reached, the concentration of hydrogen ions is\ (x\) \ (mol/L\). Since the concentration of acetate ions (CH < COO <) is approximately equal to that of hydrogen ions (ignoring the hydrogen ions produced by water ionization), then\ (K_a =\ frac {x · x} {c - x}\). Generally, the degree of ionization of weak acids is small,\ (c - x 😉 c\), so\ (x =\ sqrt {K_a · c}\), that is, the concentration of hydrogen ions\ ([H
Weak alkali solutions are similar to weak acids, and their ionization equilibrium constants need to be used. For example, ammonia (NH < unk > · H < unk > O), its ionization equilibrium constant\ (K_b =\ frac {[NH < unk > < unk > · H < unk > O]} {[NH < unk > · H < unk > O]}\). First find the hydroxide ion concentration, and then find the hydrogen ion concentration according to the ion accumulation constant of water.
For salt solutions, there are many cases. Strong acid and weak alkali salts, such as ammonium chloride (NH < unk > Cl), ammonium ion (NH < unk >) hydrolysis makes the solution acidic. Let the concentration of\ (NH Cl\) be\ (c\) \ (mol/L\), the hydrolysis constant\ (K_h =\ frac {K_w} {K_b K_b\) is the ionization equilibrium constant of ammonia water),\ (K_h =\ frac {[H 🥰] [NH 🥰 · H 🥰 O]} {[NH ₄⁺]}\) ， due to the small degree of hydrolysis,\ ([NH 🥰] Technologies c \) ，\([ NH 🥰 · H 🥰 O] Technologies [H 🥰]\), so\ ([H 🥰] =\ sqrt {K_h · c} =\ sqrt {\ frac {K_w} {K_b} · c}\).
Strong alkali and weak acid salts, such as sodium acetate (CH 🥰 COONa), acetate ion hydrolysis makes the solution alkaline. Find the hydroxide ion concentration first, and then the hydrogen ion concentration. The method is related to the above method, and is based on the ionic product constant of water and the principle of hydrolysis of salts and ionization balance of weak acids and weak bases.
In summary, to find the hydrogen ion concentration, the properties of the solution must be determined according to the different strong acids, strong bases, weak acids, weak bases, and salts, according to the corresponding principles and formulas.
If you want to know the concentration of hydrogen ions in a solution, there are various methods, which need to be reviewed in detail and selected according to different situations.
If the solution is a strong acid, the strong acid is almost completely ionized in water. For example, hydrochloric acid (HCl), one mole of hydrogen ions (H 🥰) is released per mole of HCl dissolved in water. Let the amount and concentration of the substance in the HCl solution be\ (c\) \ (mol/L\), then the concentration of hydrogen ions in the solution is\ ([H 🥰] = c\) \ (mol/L\). This is a clear reason, which is due to the ionization characteristics of strong acids.
As for the strong base solution, although mainly hydroxide ions (OH), according to the ionic product constant of water\ (K_w = [H] [OH]\), at room temperature\ (K_w = 1.0 × 10 ⁻¹⁴\) 。 If the concentration of hydroxide ions in the strong base solution is known\ ([OH]\), the hydrogen ion concentration\ ([H] =\ frac {K_w} {[OH ⁻]}\) 。 For example, in sodium hydroxide (NaOH) solution, if\ ([OH] = 0.1\) \ (mol/L\) is determined, then\ ([H 🥰] =\ frac {1.0 × 10 ◕} {0.1} = 1.0 × 10 ⁻¹³\) \( mol/L\).
The case of weak acids is more complicated. Weak acids are only partially ionized, such as acetic acid (CH 🥰 COOH), and their ionization equilibrium constant\ (K_a =\ frac {[CH 🥰 COO] [H 🥰]} {[CH 🥰 COOH]}\). Let the initial concentration of acetic acid be\ (c\) \ (mol/L\), and when the ionization equilibrium is reached, the concentration of hydrogen ions is\ (x\) \ (mol/L\). Since the concentration of acetate ions (CH < COO <) is approximately equal to that of hydrogen ions (ignoring the hydrogen ions produced by water ionization), then\ (K_a =\ frac {x · x} {c - x}\). Generally, the degree of ionization of weak acids is small,\ (c - x 😉 c\), so\ (x =\ sqrt {K_a · c}\), that is, the concentration of hydrogen ions\ ([H
Weak alkali solutions are similar to weak acids, and their ionization equilibrium constants need to be used. For example, ammonia (NH < unk > · H < unk > O), its ionization equilibrium constant\ (K_b =\ frac {[NH < unk > < unk > · H < unk > O]} {[NH < unk > · H < unk > O]}\). First find the hydroxide ion concentration, and then find the hydrogen ion concentration according to the ion accumulation constant of water.
For salt solutions, there are many cases. Strong acid and weak alkali salts, such as ammonium chloride (NH < unk > Cl), ammonium ion (NH < unk >) hydrolysis makes the solution acidic. Let the concentration of\ (NH Cl\) be\ (c\) \ (mol/L\), the hydrolysis constant\ (K_h =\ frac {K_w} {K_b K_b\) is the ionization equilibrium constant of ammonia water),\ (K_h =\ frac {[H 🥰] [NH 🥰 · H 🥰 O]} {[NH ₄⁺]}\) ， due to the small degree of hydrolysis,\ ([NH 🥰] Technologies c \) ，\([ NH 🥰 · H 🥰 O] Technologies [H 🥰]\), so\ ([H 🥰] =\ sqrt {K_h · c} =\ sqrt {\ frac {K_w} {K_b} · c}\).
Strong alkali and weak acid salts, such as sodium acetate (CH 🥰 COONa), acetate ion hydrolysis makes the solution alkaline. Find the hydroxide ion concentration first, and then the hydrogen ion concentration. The method is related to the above method, and is based on the ionic product constant of water and the principle of hydrolysis of salts and ionization balance of weak acids and weak bases.
In summary, to find the hydrogen ion concentration, the properties of the solution must be determined according to the different strong acids, strong bases, weak acids, weak bases, and salts, according to the corresponding principles and formulas.
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