Determine the mass (in g) of sodium hydrogen phosphate (Na2HPO4) that must be added to 87.8...

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Chemistry

Determine the mass (in g) of sodium hydrogen phosphate(Na₂HPO₄) that must be added to 87.8 mL of0.0264 M sodium dihydrogen phosphate to yield a pH of 7.78. Reportyour answer to 3 significant figures.

Assume the volume of the solution does not change and that the 5%approximation is valid.

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3.9 Ratings (669 Votes)

pka of phosphate buffer = 7.2

no of mole sodium dihydrogen phosphate = M*V

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = 87.8*0.0264

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = 2.32 mmole

no of mole sodium hydrogen phosphate (Na₂HPO₄) = ?

pH of acidcbuffer = pka + log(salt/acid)

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 7.78 Â Â Â Â Â = 7.2 + log(x/2.32)

Â Â Â Â Â Â Â Â Â Â Â Â Â x = no of mol of (Na₂HPO₄)Â Â = 8.82 mmole

Â Â amount of sodium hydrogen phosphate (Na₂HPO₄) = n*Mwt

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = 8.82*10^-3*142

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â = 1.25 g

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