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15240672380's Question
Chemistry
Posted 10 months ago

Y=40
Y=40

40×10−4M40 \times 10^{-4} \mathrm{M} nitric acid solution was prepared in water. Calculate the concentration of nitrate ion and the
concentration of H+H+ and OH\mathrm{OH} - ions in this solution. What is the pH\mathrm{pH} and pOH\mathrm{pOH} value?
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Answer from Sia
Posted 10 months ago
Solution
1
Identify the nature of nitric acid: Nitric acid (HNO3HNO_3) is a strong acid, which means it completely dissociates in water into H+H^+ and NO3−NO_3^- ions
2
Calculate the concentration of nitrate ion ($NO_3^-$): Since nitric acid dissociates completely, the concentration of NO3−NO_3^- will be equal to the initial concentration of nitric acid, which is 40×10−4M40 \times 10^{-4} \mathrm{M}
3
Calculate the concentration of hydrogen ion ($H^+$): Similarly, the concentration of H+H^+ will also be 40×10−4M40 \times 10^{-4} \mathrm{M} because each molecule of HNO3HNO_3 provides one H+H^+ ion upon dissociation
4
Calculate the concentration of hydroxide ion ($OH^-$): Using the water dissociation constant Kw=1.0×10−14K_w = 1.0 \times 10^{-14} at 25°C, we can find the concentration of OH−OH^- ions by the formula Kw=[H+][OH−]K_w = [H^+][OH^-]
5
Calculate the pH and pOH: The pH is calculated using the formula pH=−log⁡[H+]pH = -\log[H^+] and pOH is calculated using pOH=−log⁡[OH−]pOH = -\log[OH^-]. The sum of pH and pOH at 25°C is always 14
Answer
Concentration of NO3−NO_3^-: 40×10−4M40 \times 10^{-4} \mathrm{M}, Concentration of H+H^+: 40×10−4M40 \times 10^{-4} \mathrm{M}, Concentration of OH−OH^-: 2.5×10−11M2.5 \times 10^{-11} \mathrm{M}, pH: 3.40, pOH: 10.60
Key Concept
Strong acids completely dissociate in water, and the concentration of the ions produced is equal to the initial concentration of the acid.
Explanation
The pH is calculated from the concentration of H+H^+ ions, and the pOH is calculated from the concentration of OH−OH^- ions. For strong acids, the concentration of H+H^+ is the same as the initial concentration of the acid. The pOH can be found using the water dissociation constant and the relationship that pH + pOH = 14 at 25°C.

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