Calculate the pH of the solution that results from each of the following mixture

Question

Calculate the pH of the solution that results from each of the following mixtures.

Part A

50.0mL of 0.16M HCHO2 with 80.0mL of 0.11M NaCHO2

Express your answer using two decimal places.

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Part B

120.0mL of 0.13M NH3 with 260.0mL of 0.13M NH4Cl

Express your answer using two decimal places.

Calculate the pH of the solution that results from each of the following mixtures.

Part A

50.0mL of 0.16M HCHO2 with 80.0mL of 0.11M NaCHO2

Express your answer using two decimal places.

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Part B

120.0mL of 0.13M NH3 with 260.0mL of 0.13M NH4Cl

Express your answer using two decimal places.

Explanation / Answer

a) moles HCOOH = 0.050 L x 0.16 M=0.008
moles HCOO- = 0.0800 L x 0.11 M=0.0088
total volume = 50.0 + 80.0=130 mL = 0.130 L
concentration HCOOH = 0.008 / 0.130 = 0.06153 M
concentration HCOO- = 0.0088 / 0.130 =0.06769 M
pKa = 3.74
pH = 3.74 + log 0.06769/ 0.06153 =3.78

b)
moles NH3 = 0.120 L x 0.13 M = 0.0156
moles NH4+ = 0.260 L x 0.13 M=0.0338
total volume = 120 + 260=380 mL = 0.380 mL
concentration NH3 = 0.0156 / 0.380 =0.041052 M
concentration NH4+ = 0.0338 / 0.380 =0.0889 M
pOH = 4.74 + log 0.0889/ 0.041052 =5.075
pH = 14 - 5.075=8.925

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