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Examoogle • User • info@examoogle.com • EE-2024-8821
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If the pH of a solution is 4, what is the concentration of hydrogen ions [H+] in the solution?
10⁻⁴ mol/L
10⁻³ mol/L
4 ×10⁻¹ mol/L
10⁴ mol/L
10⁻⁴ mol/L
pH is defined as the negative base‑10 logarithm of the hydrogen‑ion concentration in a solution. For a pH value of 4, the concentration is [H+]=10−4 mol/L.
pH is defined as the negative base‑10 logarithm of the hydrogen‑ion concentration in a solution. For a pH value of 4, the concentration is [H+]=10−4 mol/L.
Think of pH like a decibel scale for sourness – each unit change represents a ten‑fold change in hydrogen‑ion intensity.
PH = -log H, so remember “PH minus log H”.
pH=−log[H+] — defines pH
[H+]=10−pH — calculates hydrogen‑ion concentration from pH
The relationship pH=−log[H+] follows from the definition of logarithms and the need for a convenient scale to express very small ion concentrations. Rearranging gives [H+]=10−pH, directly linking pH to ion concentration.
A pH decrease by one unit means the [H+] increases ten times.
The neutral pH of pure water at 25°C is 7, corresponding to [H+]=10−7 mol/L.
Provides a simple logarithmic scale to compare very dilute acidities
Does not convey the actual amount of acid present, only activity of H+
Acid‑base titration calculations
Monitoring environmental water quality
Standard neutral pH is 7, not 0 or 14.
Option B (10−3) would correspond to pH 3, not 4; Option C is a large concentration unrealistic for pH 4; Option D is absurdly high and would imply pH –4.
A is correct — the hydrogen‑ion concentration for pH 4 is 10−4 mol/L.
Remember that each unit change in pH represents a ten‑fold change in [H+], a handy trick for quick estimations in exams.