MHT CET202527 Apr 2025Evening ShiftChemistryIonic EquilibriumActual
Calculate the concentration of H ₃ O ⁺ ion if pH of solution is 2 8 .
Options
- A2.678 10⁻³ ~mol~ dm ⁻³
- B1.012 10⁻³ ~mol~ dm ⁻³
- C1.585 10⁻³ ~mol~ dm ⁻³
- D3.027 10⁻³ ~mol~ dm ⁻³
Correct answer
A. 2.678 10⁻³ ~mol~ dm ⁻³
Step-by-step solution
The hydronium ion concentration can be determined directly from the definition of pH: pH = - ₁₀[ H ₃ O ⁺] . Rearranging gives [ H ₃ O ⁺] = 10^ - pH , and substituting pH = 2.8 yields [ H ₃ O ⁺] = 10^ -2.8 . Expressing this as 10^ -2.8 = 10^ 0.2 10⁻³ yields approximately 1.58489 10⁻³ , mol ,dm ⁻³ . Rounded to four significant figures, [ H ₃ O ⁺] 1.585 10⁻³ , mol ,dm ⁻³ , corresponding to option C.