A buffer solution is prepared by mixing 300 mL of 0.10 MHNO 2 with 200 mL of 0.4
ID: 688259 • Letter: A
Question
A buffer solution is prepared by mixing 300 mL of 0.10 MHNO2 with 200 mL of 0.40 M NaNO2.a. Calculate the pH of the resulting solution.
b. What is the new pH after 2.0 mL of 2.0 M HCl are added to thisbuffer?
Matching pairs: a. pH of buffersolution — b. pH after HCladded — matching pair answers 3.3 3.7 3.8 3.9 A buffer solution is prepared by mixing 300 mL of 0.10 MHNO2 with 200 mL of 0.40 M NaNO2.
a. Calculate the pH of the resulting solution.
b. What is the new pH after 2.0 mL of 2.0 M HCl are added to thisbuffer?
Matching pairs: a. pH of buffersolution — b. pH after HCladded — matching pair answers 3.3 3.7 3.8 3.9 Matching pairs: a. pH of buffersolution — b. pH after HCladded —
Explanation / Answer
Formula: pH = pKa + log [base] / [acid] Data: [NaNO2]= 0.4 M * 0.200 L / 0.3 L +0.200L= 0.16 M
[HNO2] = 0.1 M * 0.3 L /0.3 L + 0.2L
= 0.06 M
Ka= 4.4x10-4 pKa = 3.35
Upon substituting the data in theformula, pH = 3.35 + log ( 0.16 / 0.06 ) =3.77
= 3.8
Number of moles of HNO2 = 0.1 M * 0.3L = 0.03 moles Number of moles ofNaNO2 = 0.4 M *0.2L =0.08 moles Number of moles of HCl = 0.002 L * 2.0M = 0.004 moles Chemical equation: NO2- (aq) +H+ (aq) ----------------> HNO2 (aq) Before rxn (moles) 0.08 0.03 0.004 After rxn (moles) 0.08 - 0.004 0.03 + 0.004 = 0.076 = 0.034 Upon substituting the data in to the formmula, pH = 3.35+ log ( 0.076 / 0.034 ) = 3.69
= 3.7
a) pH of buffer solution = 3.8
b) pH after adding HCl = 3.7
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