tris buffer. 50.0 g TRIS + 65.0 g TRIS•HCl ★

tris buffer. 50.0 g TRIS + 65.0 g TRIS•HCl

 

 

A TRIS/TRISH^+ buffer is prepared by

dissolving 50.0 g of TRIS and 65.0 g of TRIS•HCl

in deionized water and diluting to 2.00 L.

What is the pH of this buffer?

 

What is the pH after adding 0.5 mL of 12.0 M HCl

to a 200.0 mL portion of the buffer?

 

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▶ Tris, or tris(hydroxymethyl)aminomethane 시약의 화학식

= C4H11NO3 = NH2C(CH2OH)3

---> C4H11NO3의 몰질량 = 121.1350 ≒ 121.14 g/mol

 

 

 

 

▶ Tris hydrochloride, TRIS HCl, TRIS hydrochloride 시약의 화학식

= NH2C(CH2OH)3•HCl

---> NH2C(CH2OH)3•HCl의 몰질량 = 157.5960 ≒ 157.60 g/mol

 

 

 

 

▶ weak base tris(hydroxymethyl)aminomethane, TRIS

> (HOCH2)3CNH2의 몰질량 = 121.14 g/mol

> Kb = 1.19×10^(-6)

 

 

▶ conjugate weak acid, TRISH^+

> salt, (HOCH2)3CNH3Cl의 몰질량 = 157.60 g/mol

 

 

 

 

 

> pKb for TRIS = –log(1.19×10^(-6)) = 5.92

> pKa for TRISH^+ = 14.00 – 5.92 = 8.08

---> optimum pH range = 7.08 ~ 9.08

( 참고 https://ywpop.tistory.com/7181 )

 

 

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반응형

 

50.0 g / (121.14 g/mol) = 0.4127 mol TRIS

( 참고 https://ywpop.tistory.com/7738 )

 

65.0 g / (157.60 g/mol) = 0.4124 mol TRISH^+

 

 

 

Henderson-Hasselbalch 식

pOH = pKb + log([짝산]/[약염기])

( 참고 https://ywpop.tistory.com/1926 )

 

= 5.92 + log(0.4124 / 0.4127)

= 5.92

 

 

 

pH = 14.00 – 5.92

= 8.08

---> 완충용액의 pH

 

 

 

 

(12.0 mol/L) (0.5/1000 L) = 0.006 mol HCl

---> 가한 HCl의 몰수

 

 

 

약염기(B) 완충용액에 강산(H^+)을 가하면,

H^+(aq) + B(aq) → BH^+(aq)

---> 가한 강산의 몰수만큼,

약염기(B)의 몰수는 감소(소비),

짝산(BH^+)의 몰수는 증가(생성).

( 참고 https://ywpop.tistory.com/5442 )

 

 

 

완충용액 200.0 mL는 2.00 L의 1/10 이므로,

TRIS/TRISH^+의 몰수도 1/10.

 

 

 

pOH = 5.92 + log[ (0.0412+0.006) / (0.0413–0.006) ]

= 6.05

 

 

pH = 14.00 – 6.05

= 7.95

---> HCl 가했을 때 pH

 

 

 

 

[ 관련 예제 https://ywpop.tistory.com/search/tris%20buffer%20dic ] tris buffer dic

 

 

 

[키워드] TRIS base 50.0 g TRIS HCl 65.0 g 2.0 L buffer pH 200 mL 0.5 mL 12 M HCl, tris buffer 기준문서, tris buffer dic