Aphosphate buffer solution (25.00 ml sample) used for a growth medium was titrated with 0.1000 m hydrochloric acid. the components of the buffer were sodium monohydrogenphosphate and sodium dihydrogenphosphate. the first endpoint occurred at a volume of 10.32 ml, and the second occurred after an additional 18.62 ml was added, for a total volume of 28.94 ml. what was the total concentration of phosphate (in any form) in the buffer?

0,07448M of phosphate buffer

Explanation:

sodium monohydrogenphosphate (Na₂HP) and sodium dihydrogenphosphate (NaH₂P) react with HCl thus:

Na₂HP + HCl ⇄ NaH₂P + NaCl (1)

NaH₂P + HCl ⇄ H₃P + NaCl (2)

The first endpoint is due the reaction (1), When all phosphate buffer is as NaH₂P form, begins the second reaction. That means that the second endpoint is due the total concentration of phosphate that is obtained thus:

0,01862L of HCl×= 1,862x10⁻³moles of HCl ≡ moles of phosphate buffer.

The concentration is:

= 0,07448M of phosphate buffer

I hope it helps!

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