What is the concentration moles/liter of nitric acid solution having PH of 4?
Correct answer: A. 0.0001 mol/L
- A. 0.0001 mol/L
- B. -4
- C. 10-4 mol/L
- D. 10-10
Explanation
To determine the concentration of nitric acid in moles per liter with a pH of 4, we apply the formula: pH = -log[H+]. Rearranging gives [H+] = 10-pH. Substituting pH = 4 yields [H+] = 10-4 = 0.0001 mol/L. Since HNO3 dissociates completely in solution, the concentration of HNO3 is equal to the concentration of H+ ions. Thus, the correct concentration is 0.0001 mol/L.Option B (-4) is incorrect because pH cannot be a negative concentration. Option C (10-4) is mathematically correct but usually expressed as 0.0001 mol/L for clarity. Option D (10-10) would relate to a much higher pH value, unsuitable for this question.
This question appeared on the ETEA MDCAT 2016 paper, which you can sit online with every answer explained.
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About pH and pOH
pH measures hydrogen ion concentration and pOH measures hydroxide ion concentration on a logarithmic scale. Calculations use pH = minus log of hydrogen ion concentration, pOH = minus log of hydroxide ion concentration and pH plus pOH equals pKw, with separate treatment of strong and weak acids and bases.
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