흰인 10.0 g 연소 500 mL 용액 25℃ 용액의 pH

흰인 10.0 g 연소 500 mL 용액 25℃ 용액의 pH

10.0 g white phosphorus burn water 500 mL solution pH

 

 

흰인 10.0 g이 충분한 산소 하에서 연소되었다.

생성물을 충분한 물에 녹여서 500 mL 용액을 만들었다면

25℃에서 이 용액의 pH는 얼마이겠는가?

 

 

A 10.0 g sample of white phosphorus

was burned in an excess of oxygen.

The product was dissolved in enough water

to make 500 mL of solution.

Calculate the pH of the solution at 25°C.

 

 

A 10.0 g sample of white phosphorus, P4

was burned in oxygen and

the product was dissolved in water

to make 500.0 mL of solution.

The reactions are given below.

Calculate the pH of the solution at 25°C.

 

The balanced equation for the combustion

of white phosphorus in oxygen is:

P4(s) + 5O2(g) → P4O10(s)

 

When the product is dissolved in water,

the following reaction occurs:

P4O10(s) + 6H2O(l) → 4H3PO4(aq)

 

For phosphoric acid:

Ka1 = 7.5×10^(-3)

Ka2 = 6.2×10^(-8)

Ka3 = 4.2×10^(-13)

 

---------------------------------------------------

 

P4의 몰질량 = 123.90 g/mol 이므로,

10.0 g / (123.90 g/mol) = 0.08071 mol P4

( 참고 https://ywpop.tistory.com/7738 )

 

 

 

P4 : P4O10 : H3PO4 = 1 : 1 : 4 계수비(= 몰수비) 이므로,

0.08071 mol P4 반응 시,

4 × 0.08071 = 0.32284 mol H3PO4 생성.

 

 

 

H3PO4 용액의 몰농도

= 용질 mol수 / 용액 L수

= 0.32284 mol / 0.5000 L

= 0.64568 M

≒ 0.646 M

 

 

 

Ka1 > Ka2 > Ka3 이므로,

Ka2, Ka3 결과 이온화되는 [H^+]는 무시.

 

 

 

H3PO4(aq) ⇌ H^+(aq) + H2PO4^-(aq)

Ka1 = (x) (x) / (C–x) = 7.5×10^(-3)

( 참고 https://ywpop.tistory.com/4294 )

 

 

 

C–x ≒ C 라 근사처리하면,

x^2 / 0.646 = 7.5×10^(-3)

 

x = [(7.5×10^(-3)) × 0.646]^(1/2)

= 0.0696 M = [H^+]

 

 

 

0.646 M × (5/100) = 0.0323 M < 0.0696 M

---> 근사처리 불가능.

 

 

 

x^2 / (0.646–x) = 7.5×10^(-3)

 

x^2 + (7.5×10^(-3))x – (7.5×10^(-3))(0.646) = 0

 

 

 

근의 공식으로 x를 계산하면,

( 참고: 근의 공식 계산기 https://ywpop.tistory.com/3302 )

 

x = 0.065957 M = [H^+]

 

 

 

pH = –log[H^+]

= –log(0.065957)

= 1.18

 

 

 

답: pH = 1.18

 

 

 

 

[ 관련 예제 https://ywpop.tistory.com/11453 ] 0.0302 M 인산 용액의 pH

 

 

 

[키워드] 인산 용액의 pH 기준문서, H3PO4 용액의 pH 기준문서, white phosphorus 기준문서, 흰인 기준문서, 백린 기준문서, 백린탄 기준문서, A 5.0 g sample of white phosphorus was burned in an excess of oxygen. The product was dissolved in enough water to make 250.0 mL of solution. Calculate the pH of the solution at 25°C.