Homework Answers
1)
pH = 3.00
pKa = 3.20
moles of HF = 200 x 0.15 / 1000 = 0.030 mol
pH = pKa + log [salt / acid]
3.00 = 3.20 + log [KF / 0.030]
moles of KF = 0.0189
mass of KF added = 0.0189 x 58
mass of KF added = 1.10 g
2)
mmoles of HCN = 75 x 0.1 = 7.5
mmoles of NaCN = 100 x 0.1 = 10
mmoles of NaOH = 2 x 1 = 2
pH = pKa + log [salt + C / acid - C]
=9.305 + log [10 + 2 / 7.5 - 2]
pH = 9.64
3)
pH = pKa + log [NaCNO / HCNO]
4.00 = 3.456 + log [NaCNO / 0.1 x 0.2]
moles of NaCNO = 0.070
mass of NaCNO = 0.07 x 65
= 4.55 g
Note : I took the pKa values from the appendix which i have. please check once whether these match with your values or not. if any doubt ask me. if any wrong that is only with pKa values
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