1) 0.3 moles sodium hydroxide (HO- Na+) are mixed with 1.8 moles of formic acid
ID: 480958 • Letter: 1
Question
1) 0.3 moles sodium hydroxide (HO- Na+) are mixed with 1.8 moles of formic acid (HCOOH). What is the pH of the resulting solution? The pKa of formic acid is 3.75 (2 decimal places)
2) A pH 7.00 buffer was created by mixing 0.063 moles of HPO42-with 0.1 moles of H2PO4-. What is the pH of this solution after the addition of 0.005 moles of HCl? (The pKa of H2PO4-= 7.20) 3 significant figures.
3) 400.0 mL of 0.100 M sodium acetate (CH3COO- Na+) are mixed with 600.0 mL of 0.100 M acetic acid (CH3COOH). What is the pH of the resulting solution? The pKa of acetic acid is 4.76 (2 decimal places)
Explanation / Answer
Equation:
HCOOH + NaOH HCOONa + H2O
1 mol NaOH reacts with 1 mol HCOOH to produce 1 mol HCOONa
The pKa of formic acid is 3.75
pH calculated using Henderson - Hasselbalch equation:
pH = pKa + log ([salt]/[acid])
pH = 3.75+log ( 0.3/1.8)
pH = 3.75 + log 0.166
pH = 3.75 + (-0.7)
pH = 3.05
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