What is the pH of a buffer composed of 0.500 M sodium acetate and 0.75 M acetic

Question

What is the pH of a buffer composed of 0.500 M sodium acetate and 0.75 M acetic acid. What is the pH of the solution after 0.01 moles of hydrochloric acid is added to 1.250 L of this buffer? Fill in the blanks 8. pH of the buffer to Start: Write the buffer reaction Create the Ice Box Write the Ka for the buffer reaction Fill in the Ka from the ice box and Solve for X Find pH H of the buffer after 0.01 mols of HCl is added to 1.250 L of this buffer Write the neutralization Reaction Create the Stoichiometry box remember always enter values in terms of MOLARITY Solve for new values of conjugate acid/base pairs Write the buffer reaction Create the Ice Box (the values of conjugate acid/base pairs are from stoichiometry box) Write the Ka Experssion Fill in Ka from buffer box and Solve for X Find pH

Explanation / Answer

According to Henderson-Hasselbalch equation, pH of acidic buffer mixture is

pH=pKa+log[salt]/[acid]

Ka of acetic acid is 1.7*10^-5

pKa= -log Ka= -log1.7*10^-5 = 4.75

pH= 4.75+log[0.500]/[0.75]

pH= 4.75 + log 0.66

pH=4.75 + (- 0.176)= 4.574

CH3CO2Na + HCl => CH3CO2H + NaCl

Moles of CH3CO2H = 0.75 + 0.01 = 0.76 mol

Moles of CH3CO2- = 0.500 - 0.01 = 0.49 mol


pH = pKa + log([CH3CO2-]/[CH3CO2H])

= 4.74 + log(moles of CH3CO2-/moles of CH3CO2H)

= 4.74 + log(0.49/0.76)
= 4.74 + log(0.49/0.76)

= 4.74 + (- 0.191)

= 4.549

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