355 mL 6.5 g NaH2PO4 8.0 g Na2HPO4 pH

355 mL 6.5 g NaH2PO4 8.0 g Na2HPO4 pH

 

 

A buffer, consisting of H2PO4^- and HPO4^2-,

helps control the pH of physiological fluids.

Many carbonated soft drinks also use this buffer system.

What is the pH of a soft drink in which the major buffer ingredients are

6.5 g of NaH2PO4 and 8.0 g of Na2HPO4 per 355 mL of solution?

 

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NaH2PO4의 몰질량 = 119.98 g/mol 이므로,

6.5 g / (119.98 g/mol) = 0.0541757 mol NaH2PO4

( 참고 https://ywpop.tistory.com/7738 )

 

 

Na2HPO4의 몰질량 = 141.96 g/mol

8.0 / 141.96 = 0.0563539 mol Na2HPO4

 

 

 

H2PO4^-(aq) ⇌ H^+(aq) + HPO4^2-(aq) ... Ka2

pKa2 = –log(6.2×10^(-8)) = 7.2076 = 7.2

( 참고 https://ywpop.tistory.com/7182 )

 

 

 

Henderson-Hasselbalch 식

pH = pKa + log([짝염기]/[약산])

( 참고 https://ywpop.tistory.com/1926 )

 

= 7.2076 + log(0.0563539 / 0.0541757)

= 7.2247

 

 

 

답: pH = 7.2

 

 

 

 

[키워드] 인산 완충 용액 기준문서, 인산염 완충 용액 기준문서, NaH2PO4 완충 용액 기준문서, NaH2PO4 완충 용액의 pH 기준문서, NaH2PO4 buffer pH 기준문서