Ion product constant of water

Constant of the proportional relationship between hydrogen and oxygen ions and H2O in solution

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zero

synonym Ionic product of water (Ionic product of water) generally refers to the ionic product constant of water

The ion product constant of water, referred to as the ion product of water, refers to the hydrogen, oxygen and H ions in the solution two The constant of the proportional relationship of O. c(H + )·c( OH - ）=K (W), where K (W) is called the ionic product constant of water, c (H + ）And c (OH - ）It refers to the whole solution Hydrogen ion and Hydroxyl ion Total of Amount and concentration of substance 。 K (W) only changes with temperature, yes Temperature constant 。 because Ionization of water It is endothermic, temperature rise, equilibrium Forward shift Therefore, K (W) only increases with the increase of temperature.

Chinese name: Ion product constant of water
Abbreviation: Ionic product of water
Definition: Oxyhydrogen ion and H two Constant of the proportional relationship of O

Alphabetic representation: K(W)
Formula: c(H + )·c(OH - )=K(W)
Role: Use the ionic product constant of water to simply judge the pH value of solution

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Ionization of water

water It is extremely weak electrolyte , can produce weak ionization ionization equation Is: H two O+H two O≒H three O + + OH - , abbreviated as H two O≒H + + OH - , is an endothermic process. Water ionization is caused by the interaction between water molecules, so it is extremely difficult to occur, about 55.5 × 10 seven Only one of the water molecules is ionized.

According to the experiment, there is only 1 × 10 in 1L pure water at 25 ℃ -7 The water molecule of mol is ionized. H ionized by water molecule + And OH - The number is always the same in any case. At 25 ℃, c (H + )=c(OH - )=1×10 -7 mol/L。

c(H + )·c(OH - ）=K (W), where K (W) is called Ion product constant of water , short for Ionic product of water, c(H + ）And c (OH - ）It refers to the whole solution Hydrogen ion and Hydroxyl ion Total of Amount and concentration of substance , K (W) only changes with temperature, yes Temperature constant 。 If 25 ℃, c (H + )=c(OH - )=1×10 -7 mol/L，K(W)=1×10 -14 ； At 100 ℃, K (W)=1 × 10 -12 。 In the solution of other substances, such as acid, alkali and salt, due to ionization and hydrolysis of solute, H + Or OH - The concentration of Ionization of water , so water Ionization equilibrium It also moves to the left, so the ionic product constant of water can be used to simply judge the PH value 。

C (H) in dilute acid solution + ）Acid · c (OH - ）Water=1 × 10 -14 , c (H) in dilute alkali solution + ）Water · c (OH - ）Alkali=1 × 10 -14 。

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At room temperature, dilute solution Medium c (H + ）And c (OH - ）Of Ionic product Always 1.0x10 -14 , knowing c (H + ）C (OH - ）And vice versa. At room temperature, Acid-base property And c (H) in solution + ）And c (OH - ）The relationship of is as follows:

1. In acid solution: c (H + ）＞c(OH - )，c（H + ）＞1.0x10 -7 mol/L

two Neutral solution Middle: c (H + ）=c(OH - )=1.0x10 -7 mol/L

three Alkaline solution Middle: c (H + ）＜c(OH - )，c（H + ）＜1.0x10 -7 mol/L

Therefore, c (H + ）And c (OH - ）Both can indicate the acidity and alkalinity of the solution.

PH vs. c (H + ）Relationship between: pH is c (H + ）Negative of logarithm , that is, pH=- lg c (H + )。^[1]

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Ion product constant of water at different temperatures
t/℃	zero	ten	twenty	twenty-five	forty	fifty	ninety	one hundred
K w /10 -14	zero point one one four	zero point two nine two	zero point six eight one	one point zero one	two point nine two	five point four seven	thirty-eight	fifty-five

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