"a solution that contains 1.16% C₂H₅NH₂ by mass and 1.24% C₂H₅NH₃Br by mass"
Refer to:
https://faculty.ncc.edu/LinkClick.aspx?fileticket=ZxmmjQwsn1w%3D&tabid=1900
Kb for C₂H₅NH₂ = 5.6 × 10⁻⁴
(Different sources may give different values of Kb, and this may lead to slightly different answer.)
Molar mass of C₂H₅NH₂ = (12.0×2 + 1.0×7 + 14.0) g/mol = 45.0 g/mol
Molar mass of C₂H₅NH₃Br = (12.0×2 + 1.0×8 + 14.0 + 79.9) g/mol = 125.9 g/mol
Assume that the mass of the solution is m g.
No. of moles of C₂H₅NH₂ = (1.16%m g) / (45.0 g/mol) = 0.000258m mol
No. of moles of C₂H₅NH₃⁺ = No. of moles of C₂H₅NH₃Br = (1.24% g) / (125.9 g/mol) = 0.0000985m mol
[C₂H₅NH₃⁺]/[ C₂H₅NH₂] = 0.0000985/0.000258
C₂H₅NH₂(aq) + H₂O(l) ⇌ C₂H₅NH₃⁺(aq) …… 5.6 × 10⁻⁴
Henderson-Hasselbalch equation :
pOH = pKb + log([C₂H₅NH₃⁺]/[ C₂H₅NH₂])
pOH = -log(5.6 × 10⁻⁴) + log(0.0000985/0.000258) = 2.83
pH = pKw - pOH = 14.00 - 2.83 = 11.17
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"a solution that is 14.0 g of HC₂H₃O₂ and 10.5 g of NaC₂H₃O₂ in 150.0 mL of solution"
Refer to:
http://www4.ncsu.edu/~franzen/public_html/CH201/data/Acid_Base_Table.pdf
Ka for HC₂H₃O₂ = 1.8 × 10⁻⁵
(Different sources may give different values of Kb, and this may lead to slightly different answer.)
Molar mass of HC₂H₃O₂ = (1.0×4 + 12.0×2 + 16.0×2) g/mol = 60.0 g/mol
Molar mass of NaC₂H₃O₂ = (23.0 + 1.0×3 + 12.0×2 + 16.0×2) g/mol = 82.0 g/mol
Molar mass of HC₂H₃O₂ = (14.0 g) / (60.0 g/mol) = 0.233 mol
Molar mass of NaC₂H₃O₂ = (10.6 g) / (82.0 g/mol) = 0.129 mol
[C₂H₃O₂⁻]/[HC₂H₃O₂] = [NaC₂H₃O₂]/[HC₂H₃O₂] = 0.129/0.233
HC₂H₃O₂(aq) ⇌ C₂H₃O₂⁻(aq) + H⁺(aq) …… Ka = 1.8 × 10⁻⁵
Henderson-Hasselbalch equation :
pH = pKa + log([C₂H₃O₂⁻]/[HC₂H₃O₂])
pH = -log(1.8 × 10⁻⁵) + log(0.129/0.233) = 4.49