Calculate the pH of a solution made by adding 42 g of sodium acetate. NaCH_3COO,

Question

Calculate the pH of a solution made by adding 42 g of sodium acetate. NaCH_3COO, to 13 g of acetic acid, CH_3COOH, and dissolving in water to make 900. mL of solution. The K_a for CH_3COOH is 1.8 times 10^-5 M. As usual, report pH to 2 decimal places. Calculate the pH of a solution made by adding 79 g of sodium acetate. NaCH_3COO, to 32 g of acetic acid, CH_3COOH, and dissolving in water to make 400. mL of solution. Calculate the pH of a solution made by adding 22.0 g of sodium formate, NaHCOO, to 400. mL of 0.75 M formic acid. HCOOH. Hint what kind of solution is made? The K_a for HCOOH is 1.8 times 10^-4 M. As usual, report pH to 2 decimal places. Calculate the pH of a solution made by adding 13.0 g of sodium formate, NaHCOO, to 100. mL of 0.34 M formic acid, HCOOH.

Explanation / Answer

1)

[NaCH3COO] = mass/(molar mass * volume)
= 42 g/(82.0 g/mol * 0.900 L)
= 0.569 M

[CH3COOH] = mass/(molar mass * volume)
= 13 g/(60.0 g/mol * 0.900 L)
= 0.241 M

Ka = 1.80E-5

pKa = - log (Ka)
= - log(1.80E-5)
=4.745

use:
pH = pKa + log {[conjugate base]/[acid]}
= 4.745+ log {0.569/0.241}
=5.118

Answer: 5.12

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