Question

number 15 work and explanation please

Options A and C are equalily optimal A. C. 14. Which of the following combinations will result in a buffer solution when dissolved in D. 100. mL of water? A. 0.20 mol HF and 0.10 mol NaOH B. 0.20 mol HBr and 0.10 mol NHs C 0.20 mol NaCI and 0.10 mol HCI D. None of these. 15. How many grams of Na2COs (molar mass 106 g/mol) must be added to 1.00 L of 0.100 M NaHCOs to prepare a buffer with pH 10.00? The pK, of HCOs is 10.33. lo -16.33 A. 2.82 ED 4.98 g C. 10.7 g D. 22.5 g 16. What is the pH of a buffered solution that is 0.25 M in HCN and 0.170 M in KCN? The Ka of hydrocyanic acid (HCN) is 4.9 x 1010, A. 4.53 B. 4.86 C. 9.14

Answer 1

Explanation of work 15

The equation for the buffer equilibrium is

HCO^-3 + H₂O ⇌ CO₂^-3 + H₃O⁺; pK_a = 10.33

Let's rewrite this equation as

HA + H₂O ⇌ A^- + H₃O⁺

The Henderson-Hasselbalch equation is

pH = pK_a + log([A^-]/[HA])

10 10.33+ log HA

[HaJ= 10-0.33

142)= 100.33 [AT]

0.1 0.1 A-1 = 0.0468 M 100.33 2.138

0.0468 mol A^- Na₂CO₃ in enough water to make 1 L of solution.

The masses of Na2CO3:

Mass of Na₂CO₃ = 0.0468 mol Na₂CO₃ × [106 g Na₂CO₃ /1mol Na₂CO₃]= 4.9608 g  Na₂CO₃