Name: ph and poh in water
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 41 s
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Концентрация ионов гидроксония в водном растворе обычно записывается с отрицательными показателями степени и может составлять всего 1 10⁻¹⁴ M.Шкала pH была разработана химиком Сореном Соренсоном в 1909 году как более удобный способ быстро сравнить кислотность разных растворов. pH раствора это отрицательный логарифм концентрации ионов гидроксония. Например, раствор с концентрацией гидроксония 1 10⁻⁵ М имеет pH 5.Чем выше концентрация ионов гидроксония в растворе, тем ниже его pH. Поскольку pH выражается в логарифмической шкале, изменение на одну единицу соответствует 10-кратному увеличению или уменьшению концентрации иона гидроксония. Раствор с pH равным 3 будет иметь в десять раз больше ионов гидроксония, чем раствор с pH равным 4, и в сто раз больше, чем раствор с pH равным 5.Кислый раствор имеет более высокую концентрацию ионов гидроксония, чем гидроксид-ионов, и pH менее 7, тогда как основный раствор имеет более низкую концентрацию ионов гидроксония, чем гидроксид-ионов, и pH более 7. Нейтральный раствор с равной концентрацией ионов гидроксония и гидроксида имеет pH равный 7. Концентрация гидроксид-ионов также может быть выражена как pOH.pOH отрицательный логарифм концентрации гидроксид-иона. Чем выше концентрация гидроксид-иона, тем ниже его значение pOH. Значение pH или pOH водного раствора находится в диапазоне от 0 до 14.Это потому, что Kw, константа равновесия для автоионизации воды, равна 1 10⁻¹⁴. Отрицательный логарифм обеих частей уравнения приводит к уравнению, в котором pKw равно сумме pH и pOH. Поскольку отрицательный логарифм 1 10⁻¹⁴ равен 14, сумма pH и pOH водного раствора всегда будет равна 14.Его можно использовать для определения значения pH, если известно значение pOH, и наоборот. Например, раствор с pOH равным 10 имеет pH равный 4.

<ol>
	<li>ван Любек, Хенк. «Почему бы не заменить pH и pOH только одним реальным классом кислотности, AG?. Журнал химического образования 76, No7 (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>

шкала ph

Ионы гидрония и гидроксида присутствуют как в чистой воде, так и во всех водных растворах, и их концентрации обратно пропорциональны, как определено ионным продуктом воды (кВт). Концентрации этих ионов в раствор часто являются критическими детерминантами свойств решения и химического поведения других его солей. Два различных решения могут отличаться в концентрациях гидрония или гидроксида ионов в миллионах, миллиардах или даже триллионах раз. Общераспространенным средством выражения величин, которые могут охватывать многие порядки величины, является использование логарифмической шкалы. Таким образом, pH раствор определяется, как показано на рисунке, где [H3O+] — молярная концентрация гидрония в ионе раствор: 
  <img alt="Eq1" src="/files/ftp_upload/11397/11397_Equation_1.png" style="height: 50px;" />
 Переупорядочивание этого уравнения для изоляции молярности ионов гидрония дает эквивалентное выражение: 
  <img alt="Eq2" src="/files/ftp_upload/11397/11397_Equation_2.png" style="height: 50px;" />
 Также молярность ионов гидроксида может быть выражена как p-функция или Poh: 
  <img alt="Eq3" src="/files/ftp_upload/11397/11397_Equation_3.png" style="height: 50px;" />
 или 
  <img alt="Eq4" src="/files/ftp_upload/11397/11397_Equation4.png" style="height: 50px;" />
 Наконец, соотношение между этими двумя ионными концентрациями, выраженными как p-функции, легко вытекает из выражения KW: 
  <img alt="Eq5" src="/files/ftp_upload/11397/11397_Equation_5.png" style="height: 135px;" />
 При 25 °C значение КВТ составляет 1.0 × 10-14, и поэтому: 
  <img alt="Eq6" src="/files/ftp_upload/11397/11397_Equation_6.png" style="height: 50px;" />
 Молярность ионов гидрония в чистой воде (или любом нейтральном раствор) составляет 1.0 × 10-7 M при 25 °C. Поэтому pH и Poh нейтрального раствор при этой температуре: 
  <img alt="Eq7" src="/files/ftp_upload/11397/11397_Equation_7.png" style="height: 95px;" />
 И поэтому при этой температуре кислотные растворы являются растворами с гидронионными ионными молярностями, превышающими 1.0 × 10-7 M, и молярностью гидроксидных ионных ионов менее 1.0 × 10-7 M (соответствующими значениям pH менее 7.00 и значениям Poh больше 7.00). Основными растворами являются растворы с молярностью гидрония иона менее 1.0 × 10-7 M и молярностью гидроксида иона более 1.0 × 10-7 M (соответствующие значениям pH больше 7.00, а значения Poh меньше 7.00). 
 Поскольку константа автоматической ионизации КВТ зависит от температуры, эти корреляции между значениями pH и кислотными/нейтральными/основными прилагательными будут отличаться при температурах, отличных от 25 °C. Например, молярность гидрония чистой воды при 80°C составляет 4.9 × 10-7 м, что соответствует значениям pH и Poh: 
  <img alt="Eq8" src="/files/ftp_upload/11397/11397_Equation_8.png" style="height: 95px;" />
 При этой температуре нейтральные растворы демонстрируют pH = Poh = 6.31, кислотные растворы имеют pH менее 6.31 и Poh больше 6.31, тогда как базовые растворы имеют pH больше 6.31 и Poh меньше 6.31. Это различие может быть важно при изучении некоторых процессов, которые происходят при других температурах, таких как реакции фермента в теплокровных организмах при температуре около 36 – 40 °C. Если не указано иное, ссылки на значения pH считаются значениями при 25 °C. 
 Этот текст адаптирован из<a href="https://openstax.org/books/chemistry-2e/pages/14-2-ph-and-poh"> Openstax, Химия 2е изд., раздел 14.2: PH и Poh. </a>

шкала pH

Ионы гидроксония и гидроксида присутствуют как в чистой воде, так и во всех водных растворах, причем их концентрации обратно пропорциональны ...

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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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