Name: ph and poh in water
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 41 s
Channel: JoVE

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pH Scale

수용액에서 하이드로늄 이온의 농도는 보통 음의 지수로 되며 10 의 마이너스 14승 몰농도 정도로 작을 수 있습니다. pH 척도는 화학자 소렌 소렌슨이 1909년에 다른 용액의 산도를 빠르게 비교할 수 있는 더 편리한 방법으로 개발했습니다. 용액의 pH는 하이드로늄 이온 농도의 음의 대수입니다.

예를 들어, 하이드로늄 농도가 10의 마이너스 5승 몰농도인 용액의 pH는 5입니다. 용액의 하이드로늄 이온 농도가 높을수록 pH는 낮아집니다. pH는 로그 척도로 표현되므로 단일 단위 변화는 하이드로늄 이온 농도의 10배 증가 또는 감소에 해당합니다.

pH가 3인 용액은 pH 4인 솔루션보다 10배, pH 5인 솔루션보다 100배 많은 하이드로늄 이온을 가집니다. 산성 용액은 수산화 이온보다 하이드로늄 이온의 농도가 높고 pH가 7보다 적지만 염기 용액은 수산화 이온보다 하이드로늄 이온의 농도가 낮고 pH가 7보다 큽니다. 하이드로늄 이온과 수산화 이온의 농도가 동일한 중성 용액은 pH가 7입니다.

수산화물 이온의 농도는 또한 pOH로 표현될 수 있습니다. pOH는 수산화물 이온 농도의 마이너스 로그입니다. 수산화 이온 농도가 높을수록 pOH 값이 낮아집니다.

수용액의 pH 또는 pOH 값 범위는 0에서 14입니다. 물의 자동 이온화를 위한 평형 상수인 Kw가 10의 마이너스 14승이기 때문입니다. 방정식 양쪽에 음의 로그를 취하면 pKw가 pH와 pOH의 합과 같은 방정식이 됩니다.

10의 마이너스 14승의 음의 로그는 14이므로 수용액의 pH와 pOH의 합은 항상 14가 됩니다. 이 값은 pOH 값이 알려진 경우 pH 값을 결정하는 데 사용할 수 있으며 그 반대의 경우도 마찬가지입니다. 예를 들어, pOH가 10인 용액의 pH는 4입니다.

<ol>
	<li>van Lubeck, Henk. "pH와 pOH를 하나의 실제 산도 등급인 AG로 대체하지 않는 이유는 무엇입니까?. " 화학교육저널 76, no. 7 (1999): 892. <a href="https://pubs.acs.org/doi/pdf/10.1021/ed076p892">https://pubs.acs.org/doi/pdf/10.1021/ed076p892</a></li>
</ol>

ph 척도

수소이온과 수산화이온은 순수한 물과 모든 수용액에 모두 존재하며, 그 농도는 물의 이온곱(Kw)에 따라 반비례합니다. 용액 내 이러한 이온의 농도는 종종 용액의 특성과 다른 용질의 화학적 거동을 결정하는 중요한 요소입니다. 두 가지 서로 다른 용액의 수소 또는 수산화물 이온 농도는 백만, 십억, 심지어는 조만큼 다를 수 있습니다. 여러 자릿수에 걸쳐 있을 수 있는 양을 표현하는 일반적인 방법은 로그 눈금을 사용하는 것입니다. 따라서 용액의 pH는 다음과 같이 정의됩니다. 여기서 [H_3O^+]는 용액 내 하이드로늄 이온의 몰 농도입니다.

 <img alt="Eq1" src="/files/ftp_upload/11397/11397_Equation_1.png" style="height: 50px;" />

하이드로늄 이온 몰농도를 분리하기 위해 이 방정식을 재배열하면 다음과 같은 등가 표현식이 생성됩니다.

 <img alt="Eq2" src="/files/ftp_upload/11397/11397_Equation_2.png" style="height: 50px;" />

마찬가지로, 수산화물 이온 몰농도는 p-함수 또는 pOH로 표현될 수 있습니다.

 <img alt="Eq3" src="/files/ftp_upload/11397/11397_Equation_3.png" style="height: 50px;" />

또는

 <img alt="Eq4" src="/files/ftp_upload/11397/11397_Equation4.png" style="height: 50px;" />

마지막으로, p-함수로 표현된 두 이온 농도 사이의 관계는 K_W 표현에서 쉽게 파생됩니다.

 <img alt="Eq5" src="/files/ftp_upload/11397/11397_Equation_5.png" style="height: 135px;" />

25°C에서 K_W 값은 1.0 × 10−14이므로 다음과 같습니다.

 <img alt="Eq6" src="/files/ftp_upload/11397/11397_Equation_6.png" style="height: 50px;" />

순수한 물(또는 중성 용액)의 하이드로늄 이온 몰농도는 25°C에서 1.0 × 10^−7 M입니다. 따라서 이 온도에서 중성 용액의 pH와 pOH는 다음과 같습니다.

 <img alt="Eq7" src="/files/ftp_upload/11397/11397_Equation_7.png" style="height: 95px;" />

따라서 이 온도에서 산성 용액은 하이드로늄 이온 몰량이 1.0 × 10^-7 M보다 크고 수산화물 이온 몰량이 1.0 × 10^-7 M 미만인 용액입니다(pH 값이 7.00 미만이고 pOH 값이 7.00보다 큰 경우). 염기성 용액은 하이드로늄 이온 몰량이 1.0 × 10^-7 M 미만이고 수산화물 이온 몰량이 1.0 × 10^-7 M보다 큰 용액입니다(pH 값이 7.00보다 크고 pOH 값이 7.00보다 작음).

자동 이온화 상수 K_W는 온도에 따라 달라지므로 pH 값과 산성/중성/염기성 형용사 간의 이러한 상관관계는 25°C 이외의 온도에서는 달라집니다. 예를 들어, 80°C에서 순수한 물의 하이드로늄 몰농도는 4.9 × 10−7 M이며 이는 다음의 pH 및 pOH 값에 해당합니다.

 <img alt="Eq8" src="/files/ftp_upload/11397/11397_Equation_8.png" style="height: 95px;" />

이 온도에서 중성 용액은 pH = pOH = 6.31을 나타내고, 산성 용액은 pH 6.31 미만, pOH 6.31보다 큰 반면, 염기성 용액은 pH 6.31 이상, pOH 6.31 미만을 나타냅니다. 이러한 구별은 약 36~40°C 온도에서 온혈 유기체의 효소 반응과 같이 다른 온도에서 발생하는 특정 과정을 연구할 때 중요할 수 있습니다. 달리 명시하지 않는 한, pH 값에 대한 참조는 25°C에서의 값으로 추정됩니다.

이 문서는 에서 발췌되었습니다 <a href="https://openstax.org/books/chemistry-2e/pages/14-2-ph-and-poh"> Openstax, Chemistry 2e, Section 14.2: pH and pOH.</a>

pH 척도

히드로늄 및 수산화물 이온은 순수한 물과 모든 수용액 모두에 존재하며 그 농도는 다음과 같이 반비례합니다.

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ph and poh in water

pH and pOH show how hydronium and hydroxide ions behave in water and other aqueous solutions. These ion concentrations are linked by the ion product of water, K w , so when one goes up, the other goes down.

Because ion concentrations can differ by huge amounts, a logarithmic scale is used to describe them. pH is defined from the hydronium ion concentration, [H3O+], and pOH is the matching p-function for hydroxide ion concentration. These two values are also connected through the K w relationship.

At 25 °C, K w is 1.0 × 10−14. In pure water, or any neutral solution at this temperature, the hydronium ion concentration is 1.0 × 10−7 M. That gives pH = 7.00 and pOH = 7.00.

At 25 °C, acidic solutions have hydronium ion concentrations greater than 1.0 × 10−7 M and hydroxide ion concentrations less than 1.0 × 10−7 M. This means acidic solutions have pH values below 7.00 and pOH values above 7.00. Basic solutions show the opposite pattern, with pH above 7.00 and pOH below 7.00.

The link between pH and acidity changes with temperature because K w changes with temperature. For example, pure water at 80 °C has a hydronium ion concentration of 4.9 × 10−7 M, which gives pH and pOH values of 6.31. At this temperature, neutral solutions have pH = pOH = 6.31, acidic solutions have pH below 6.31, and basic solutions have pH above 6.31.

This temperature effect matters in processes that happen away from 25 °C, including enzyme reactions in warm-blooded organisms at about 36–40 °C. Unless another temperature is stated, pH values are usually assumed to refer to 25 °C.

pH and pOH in Water

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pH and pOH show how hydronium and hydroxide ions behave in water and other aqueous solutions. These ion concentrations are linked by the ion product of water, K w , so when one goes up, the other goes down. Because ion concentrations can differ by huge amounts, a logarithmic scale is used to describe them. pH is defined from the hydronium ion concentration, [H3O+], and pOH is the matching p-function for hydroxide ion concentration. These two values are also connected through the K w...

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Learn how hydronium and hydroxide ion levels define pH and pOH, why neutral water changes with temperature, and how acidic or basic solutions are identified.

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pH and pOH in Water

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