If 30 mL of 0.10 M NaOH is added to 40 mL of 0.20 M HC_2H_3O_2,. what is the pH

Question

If 30 mL of 0.10 M NaOH is added to 40 mL of 0.20 M HC_2H_3O_2,. what is the pH of the resulting solution at 25degreeC? K_a for HC_2H_3O_2, is 1.8 times 10^-5 at 25degreeC. 2. Potassium hydrogen Phthalate (KHP) is used to standardize sodium hydroxide. If 35.39 mL. of potassium hydrogen If 35.39 mL of NaOH(aq) is required to titrate 0.8246 g KHP to the equivalence point, what is the concentration of the NaOH(aq)? (The molar mass of KHP = 204.2 g/mol) HC_3H_4O_4^-(aq) + OH^-(aq) C_8H_4O^2-_4(aq) + H_2O(l)

Explanation / Answer

B.

1. to make a buffer of pH 8, the pKa of the weak acid should be close to 8. Such that the Ka would be,

pKa = 8 = -log[Ka]

Ka = 1 x 10^-8

2. Breathing in a paper bag is exhalation of CO2 from the system. This would lower the pH of the body.

C.

1. when NaOH reacts with acetic acid, sodium acetate is formed

[NaC2H3O2] formed = 0.1 M x 30 ml/70 ml = 0.043 M

[HC2H3O2] remaining = (0.2 M x 40 ml - 0.1 M x 30 ml)/70 ml = 0.071 M

pH = pKa + log(base/acid)

      = 4.745 + log(0.043/0.071)

      = 4.53

2. moles of KHP = 0.8246 g/204.2 g/mol = 0.004 mol

1mole of KHP reacts with 1 mol of NaOH

concentration of NaOH = moles/L = 0.004/0.03539 = 0.113 M

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