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pH Value
pH Value
pH (potential of Hydrogen) is defined as the decimal logarithm of the reciprocal of the hydrogen ion concentration in a solution.
pH (potential of Hydrogen) is defined as the decimal logarithm of the reciprocal of the hydrogen ion concentration in a solution.
pH Value = −lg(H+)
pH Value = −lg(H+)
H+ refers to the Hydrogen Ion Centration.
H+ refers to the Hydrogen Ion Centration.
High pH ⇔ Low concentration of H+
High pH ⇔ Low concentration of H+
A pH value less than 7 is considered acidic (High concentration of Hydrogen ions), pH value of 7 is considered neutral and a pH value greater than 7 is considered alkaline (Low concentration of Hydrogen ions)
A pH value less than 7 is considered acidic (High concentration of Hydrogen ions), pH value of 7 is considered neutral and a pH value greater than 7 is considered alkaline (Low concentration of Hydrogen ions)
Explore!
Explore!
Use the applet below to explore the relationship between Hydrogen Ion Concentration and pH Value.
Use the applet below to explore the relationship between Hydrogen Ion Concentration and pH Value.
Why use a Logarithmic Scale?
Why use a Logarithmic Scale?
From the graph above, you should notice that the concentration of H+ are ridiculously small numbers (Eg. 0.000 001 mol/dm3 vs 0.000 000 01 mol/dm3) which make them hard to tell apart just like that GREEN point seems to stick to the y-axis. A logarithmic scale allows the reader to focus on the exponent and use the exponent to gauge the concentration level.
From the graph above, you should notice that the concentration of H+ are ridiculously small numbers (Eg. 0.000 001 mol/dm3 vs 0.000 000 01 mol/dm3) which make them hard to tell apart just like that GREEN point seems to stick to the y-axis. A logarithmic scale allows the reader to focus on the exponent and use the exponent to gauge the concentration level.
Why pH 7 is neutral?
Why pH 7 is neutral?
Water is able to self-ionize. A H2O molecule can lose a proton to become a hydoxide ion (OH−) while that rouge proton (H+) will protonate another H2O molecule to form hydronium (H3O+).
Water is able to self-ionize. A H2O molecule can lose a proton to become a hydoxide ion (OH−) while that rouge proton (H+) will protonate another H2O molecule to form hydronium (H3O+).
2H2O ⇆ OH− + H3O+
2H2O ⇆ OH− + H3O+
This reaction constantly occurs and reverses almost instantly. At any point of time, only a small fraction of these water molecules are ionized and this fraction is a special constant known as the water disassociation constant, Kw ≈ 1.006 × 10−14. For water,
This reaction constantly occurs and reverses almost instantly. At any point of time, only a small fraction of these water molecules are ionized and this fraction is a special constant known as the water disassociation constant, Kw ≈ 1.006 × 10−14. For water,
Kw = [Concentration of OH−] ✕ [Concentration of H3O+]
Kw = [Concentration of OH−] ✕ [Concentration of H3O+]
At 25 °C, the concentrations of the hydronium ion and the hydroxide ion are equal.
At 25 °C, the concentrations of the hydronium ion and the hydroxide ion are equal.
∴ Concentration of OH− = Concentration of H3O+ ≈ 1.0×10−7
∴ Concentration of OH− = Concentration of H3O+ ≈ 1.0×10−7
Therefore the neutral pH Value ≈ −lg(1.0×10−7) = 7.
Therefore the neutral pH Value ≈ −lg(1.0×10−7) = 7.
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