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13 Dec 2019

what is the pH of a buffered sysem made by dissolving 17.42 g ofKH2PO4 and 20.41 g of K2HPO4 in water to give a volume of 200.0 mL?The Ka2 for dihydrogen phosphate is 6.2 X 10^-8 and the equilibriumreaction of interest is

H2PO4-(aq) + H2O(l) = H3O+(aq) + HPO4-(aq)


please show steps, thanks.

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Tod Thiel
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17 Dec 2019

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Related questions

What is the pH of a buffered system made by dissolving 17.42 gof KH2PO4 and 20.41 g ofK2HPO4 in water to give a volume of 200.0 mL?The K a2 for dihydrogen phosphate is 6.2

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A liter of pH 7.20 phosphate buffer is needed for a certain experiment. The Henderson-Hasselbach equation will be sufficiently accurate for your determination of pH. The pK’s for possibly relevant phosphate species are:

H3PO4 ↔ H2PO4- + H+ pK = 2.15

H2PO4- ↔ HPO4-2 + H+ pK = 7.20

HPO4-2 ↔ PO4-3 + H+ pK = 12.4

0.100 Moles of H3PO4 were dissolved in about 800 mL of water, and the pH was adjusted to 7.20 using a standardized pH meter and a 1 M solution of KOH followed by addition of water to a volume of 1.00 L.

a. (10 pts) Write the equation for the charge balance to show how [K+], [H2PO4-], and [HPO4-2] are related. ([H+] and [OH-], although they are charged species, can be neglected for charge balance when compared to [K+], [H2PO4-], and [HPO4-2])

b. (10 pts) At pH 7.20 what is the ratio of [H2PO4-] to [HPO4-2]?

c. (20 pts) Combine your findings from parts a and b to determine how many mL of 1 M KOH must be added. {An important hint: By mass balance, the total molar concentration of phosphate species at pH 7.2 must equal the total molar concentration of phosphate species that was added from H3PO4.}

PLEASE ANSWER ALL PARTS, I NEED HELP. THANKS IN ADVANCE!

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