Ionization of Water, Weak Acids, and Weak Bases: -The Ionization of Water Is Expressed by an Equilibrium Constant

The degree of ionization of water at equilibrium (Eqn 2–1) is small; at 25 °C only about two of every 109 molecules in pure water are ionized at any instant. The equilibrium constant for the reversible ionization of water (Eqn 2–1) is

In pure water at 25 C, the concentration of water is 55.5 M (grams of H2O in 1 L divided by its gram molecular weight: (1,000 g/L)/ (18.015 g/mol)) and is essentially constant in relation to the very low concentrations of H and OH, namely, 1x10^-7 M. Accordingly, we can substitute 55.5 M in the equilibrium constant ex pression (Eqn 2–3) to yield

which, on rearranging, becomes

(55.5 M) (Keq)= [H+] [OH-]=K_w

where Kw designates the product (55.5 M) (Keq), the ion product of water at 25 °C. The value for Keq, determined by electrical-conductivity measurements of pure water, is 1.8x10^-16 M at 25 C. Substituting this value for Keq in Equation 2–4 gives the value of the ion product of water:

Kw=[H+] [OH-]= (55.5 M) (1.8x10^-16 M)= 1.0x10^-14M₂

Thus the product [H+] [OH-] in aqueous solutions at 25 C always equals 1x10^-14 M². When there are exactly equal concentrations of H+ and OH-, as in pure water, the solution is said to be at neutral pH. At this pH, the concentration of H+ and OH- can be calculated from the ion product of water as follows:

Kw=[H+] [OH-]=[H+]²

Solving for [H⁺] gives

As the ion product of water is constant, whenever [H+] is greater than 1 than 1x10^-7 M, [OH-] must become less 10 7M, and vice versa. When [H|+] is very high, as in a solution of hydrochloric acid, [OH-] must be very low. From the ion product of water we can calculate [H+] if we know [OH-], and vice versa (Box 2–2).

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشعائر يشارك في حملة إغاثة الشعبين الإيراني واللبناني عبر منافذ العتبة العباسية المقدسة

ضمن برنامج بيوت النعيم.. قسم الشؤون الفكرية ينظّم مجلسًا عزائيًّا في بابل

المجمَع العلمي يقيم الحفل الختامي لدورتي (زينة القرآن والإتقان القرآني) في المثنى

شعبة التوجيه الديني النسوي تنظم برنامج مفتاح البصيرة الأسبوعي

المزيد

الآخبار الصحية

الشاشات ليست مجرد ترفيه.. تأثيرات طويلة المدى على دماغ طفلك

الأسباب الرئيسية لنقص الطاقة في الجسم

الكاكاو وتأثيره على العين.. نتائج واعدة من تجارب مخبرية

طبيب يحذر: أطعمة شائعة الاستهلاك أخطر على صحتنا من التدخين

المزيد

الآخبار التكنلوجية

باحثون في "نيويورك أبوظبي" يطورون تقنيات لرصد وعلاج الأورام

جيتكس إفريقيا.. المغرب يجمع "رواد التكنولوجيا" من 103 دول

طاقم أرتميس 2 يحطم رقما قياسيا ويستعرض الجانب البعيد للقمر

"أرتيميس 2" تنطلق حول القمر وتحطم الرقم القياسي

المزيد

مواضيع ذات صلة

Ionization of Water, Weak Acids, and Weak Bases: -The pH Scale Designates the H+ and OH- Concentrations

Ionization of Water, Weak Acids, and Weak Bases: - Pure Water Is Slightly Ionized

Weak Interactions in Aqueous Systems: -Solutes Affect the Colligative Properties of Aqueous Solutions

Weak Interactions in Aqueous Systems: -Weak Interactions Are Crucial to Macromolecular Structure and Function

Weak Interactions in Aqueous Systems: - van der Waals Interactions Are Weak Interatomic Attractions

Weak Interactions in Aqueous Systems: -Nonpolar Compounds Force Energetically Unfavorable Changes in the Structure of Water

Weak Interactions in Aqueous Systems: -Entropy Increases as Crystalline Substances Dissolve

Weak Interactions in Aqueous Systems: - Water Interacts Electrostatically with Charged Solutes

Weak Interactions in Aqueous Systems: -Water Forms Hydrogen Bonds with Polar Solutes

Weak Interactions in Aqueous Systems: - Hydrogen Bonding Gives Water Its Unusual Properties

Evolutionary Foundations: -Molecular Anatomy Reveals Evolutionary Relationships

Evolutionary Foundations: -Eukaryotic Cells Evolved from Prokaryotes in Several Stages