47. Nitrous acid, HNO2(aq), has a Ka of 4.5x 10-4 at 25°C. What is the pH of a s

Question

47. Nitrous acid, HNO2(aq), has a Ka of 4.5x 10-4 at 25°C. What is the pH of a solution that contains 1.0 M KNO2(aq) and 0.50 M HNO2(aq)? (A) 0.183 (B) 3.05 (C) 3.35 CD) 3.65 48. Consider a buffer solution containing HCN and NaCN where the concentration of HCN is double the concentration of NaCN. Which statement about the buffer solution is true? (A) The pH of this solution is equal to the pKa value of (B) The pK, vaue of HCN will decrease if a strong acid (C) The buffer capacity of this solution will improve if a (D) The cyanide ion concentration will increase if a HCN is added. strong acid is added. strong base is added. If25.0 mL of 0.750 M HCl are added to 100. mL of 0.352 M NaOH, what is the final pH? The volumes are additive. 49. (A) 13.45 (B) 13.12 (C) 7.00 (D) 0.40

Explanation / Answer

47)

Ka = 4.5*10^-4

pKa = - log (Ka)

= - log(4.5*10^-4)

= 3.347

we have below equation to be used:

This is Henderson–Hasselbalch equation

pH = pKa + log {[conjugate base]/[acid]}

pH = pKa + log {[KNO2]/[HNO2]}

= 3.347+ log {1/0.5}

= 3.65

Answer: D

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