6. What is the pH of the buffer that results when 12.0 g of NaH2PO4 and 8.00 g of Na2HPO4 are diluted with water to a volume of 0.50 L? (Ka of H2PO4– = 6.2 x10–8, the molar masses of NaH2PO4 and Na2HPO4 are 120.0 g/mol and 142.0 mol, respectively)

Therefore of the buffer solution is 6.96.

Explanation:

The Henderson- Hasselbalch Equation:

.

The acid will be H₂PO₄⁻ and the salt of the acid will be HPO₄²⁻.

Given the molar mass of  NaH₂PO₄ is 120.0 g/mol and the molar mass of Na₂HPO₄ is 142.0g/mol.

The number of mole of 12 gram of NaH₂PO₄ is

=0.1 mole

The number of mole of 8 gram of Na₂HPO₄ is

=0.056 mole.

Concentration of [H₂PO₄⁻ ] is

=0.2 M

Concentration of [HPO₄²⁻] is

=0.112 M

Therefore ,

Therefore of the buffer solution is 6.96.

b is the correct answer

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