Demonstrating the common-ion effect: (a) Determine the [H^+] and [C_2H_3O_2] in

Question

Demonstrating the common-ion effect: (a) Determine the [H^+] and [C_2H_3O_2] in 0.1M HC_2H_3O_2, (b) Determine the same values in a solution that contains 0.1M HC_2H_3O_2 and 0.1M HCl. (Ka for is HC_2H_3O_2 1.8 times 10^-3.) Demonstrating the common-ion effect: What is the pH of the solutions in (a) and (b) above? Explain why we subtract X from HA in both problems. Doesn't this seem contrary to lessthanorequalto Chatelier's Principal? Whether a solution is a buffer solution: Show that NH_3 and NH_4Cl solution is it buffer using formulas for Ka + kb. Based on this example, use formulas to explain why K_ = Ka + Kb Calculating the pH of a buffer solution: What is the pH of a buffer prepared by dissolving 25.5g of NaC_2H_3O_2, (FW = 82.04g mol) in 0.550M HC_2H_3O_2 at Vt = 500mL? (pKa = 4.74) Preparing a buffer of a desired pH: What mass of NaC_2H_3O_2 must be dissolved in 300mL of 0.25M HC_2H_3O_2 to obtain a pH = 5.09 (Assume that the Vt stays constant at 300mL!!!) (pKa = 4.74) Calculating pH changes in a buffer solution: What are the effects on pH by adding 0.06mol HCL to 0.3L of a buffer that contains 0.25M HC_2H_3O_2 and 0.56M NaC_2H_2O? (pKa = 4.74)

Explanation / Answer

Q4

for a buffer: apply henderson hasselbach equations

pH = pKa + log(A-/HA)

A- = conjguate base, NaAc

HA = weak acid, Acetic acid

mol NaAc = mass/MW = 25.5/82.04 = 0.3108

[NaAc] = 0.3108/0.5 = 0.6216 M

[HAc] = mass/MW = 0.55

pH = 4.74 + log(0.6216 /0.55)

pH = 4.79314

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