SME
Grade 10 Science · Problem type
[H⁺] from pH
Use this for “A solution has a pH of 8.50. What is its [H⁺]?”
Diagram
Since pH = −log₁₀[H⁺], here [H⁺] = 10⁻⁸·⁵ = 3.1623 × 10⁻⁹ mol/L.
Above 7: basic. pOH = 14 − pH = 5.5.
This is an example. Type your own values to start a new problem.
[H⁺]
=
10
−
=
[H⁺] (mol/L)
Formulas
pH = −log₁₀([H⁺])
8.5
=
−log₁₀(3.16
×
10
-9
)
Assumptions
•
The water is at 25 °C, where [H⁺][OH⁻] = 1 × 10⁻¹⁴ and pH + pOH = 14.
•
Each pH unit is ten times the [H⁺]. Below 7 is acidic, above 7 basic.
Step-by-step
WE KNOW
pH = 8.5
FIND
hydrogen ion concentration ([H⁺])
Step 1 · Find hydrogen ion concentration ([H⁺])
Use pH = −log₁₀([H⁺])
Undo the log: 10 to the power of minus the value.
[H⁺] = 10−pH
[H⁺]
=
10
−8.5
[H⁺]
=
3.16 ×
10
-9
mol/L
Check
Put the numbers back in. Both sides should match.
8.5
≈
−log₁₀(3.16
×
10
-9
)
✓
Topic check
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