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6) You are making 100 mL of 1 M phosphate buffer [pKa,1 = 2.12; pKa,2 = 7.21; pka,3 12.33] at pH 7. How many moles of buffer are in each of the following forms? H3PO4 = ● ● H₂PO4 = HPO4 = PO4 = =

6) You are making 100 mL of 1 M phosphate buffer [pKa,1 = 2.12; pKa,2 = 7.21; pka,3 12.33] at pH 7. How many moles of buffer are in each of the following forms? H3PO4 = ● ● H₂PO4 = HPO4 = PO4 = =

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Chemistry
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ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
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### Problem 6 You are making 100 mL of 1 M phosphate buffer \([pK_{a,1} = 2.12; \, pK_{a,2} = 7.21; \, pK_{a,3} = 12.33]\) at pH 7. How many moles of buffer are in each of the following forms? - **H₃PO₄ =** _______ - **H₂PO₄⁻ =** _______ - **HPO₄²⁻ =** _______ - **PO₄³⁻ =** _______ ### Explanation This question involves calculating the distribution of the different forms of a phosphate buffer at a given pH. It asks for the number of moles of each species (H₃PO₄, H₂PO₄⁻, HPO₄²⁻, PO₄³⁻) in the buffer system at pH 7. The solution depends on understanding the relationship between pH, pKa values, and the equilibrium concentrations of the buffer components.
Transcribed Image Text:### Problem 6 You are making 100 mL of 1 M phosphate buffer \([pK_{a,1} = 2.12; \, pK_{a,2} = 7.21; \, pK_{a,3} = 12.33]\) at pH 7. How many moles of buffer are in each of the following forms? - **H₃PO₄ =** _______ - **H₂PO₄⁻ =** _______ - **HPO₄²⁻ =** _______ - **PO₄³⁻ =** _______ ### Explanation This question involves calculating the distribution of the different forms of a phosphate buffer at a given pH. It asks for the number of moles of each species (H₃PO₄, H₂PO₄⁻, HPO₄²⁻, PO₄³⁻) in the buffer system at pH 7. The solution depends on understanding the relationship between pH, pKa values, and the equilibrium concentrations of the buffer components.
Expert Solution
Step 1

Required pH of the buffer solution, pH = 7

A buffer solution is made of a weak acid and its conjugate base. 

The best constituents of a buffer solution are the acid-base pairs whose pKa value is closest to the desired pH value of the buffer solution. 

Since pH 7 is closest to the pKa2 value, we need the dihydrogenated species, H2PO4-(aq) as the weak acid and HPO42-(aq) as the conjugate base. 

 

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