المحاليل الحيوية المنظمة. s تعريف المحلول المنظّم : s هي محاليل تتغيّر قيمة الرقم الهيدروجيني لها تغيراً طفيفاً عندإضافة حمض أو قاعدة إليها بكميات قليلة.

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Presentation transcript:

المحاليل الحيوية المنظمة

s تعريف المحلول المنظّم : s هي محاليل تتغيّر قيمة الرقم الهيدروجيني لها تغيراً طفيفاً عندإضافة حمض أو قاعدة إليها بكميات قليلة. (أي أنها تقاوم التغيرات في قيمة PH لها عند إضافة حمض أو قاعدة إليها ). s ممّ يتكوّن المحلول المنظّم : s يتكوّن من : 1- حمض ضعيف وقاعدته المرافقة (ملح الحمض) أو 2- قاعدة ضعيفة وحمضها المرافق (ملح القاعدة) s أمثلة لمحاليل منظمّة : (CH3COOH ،CH3COO-) s (NH3 ، NH4Cl) (HCN ، NaCN) s (HNO2 ، KNO2) (H2CO3 ، NaHCO3)

أهمية المحلول المنظم : s يتطلب الكثير من العمليات الكيمائية والحيوية أن لا تتغير قيمة PH لوسط التفاعل كثيراً. بل تبقى قريبة من قيمة معينة. s ومثال ذلك أن الدم في جسم الإنسان لا يمكن أن يقوم بوظيفة نقل الأكسجين إلى الخلايا إلاّ أن تكون قيمة s 7.4 PH = s وللمحاليل المنظمةأهمية فمثلاً : s أ- أن الأنزيمات تحتاج لوسط تكون فيه قيمة PH ثابتة تقريباً لتعمل بنشاط. s ب- معالجة التربة لنمو المحاصيل المختلفة.

Acid-Base Titrations Adding NaOH from the buret to acetic acid in the flask, a weak acid. In the beginning the pH increases very slowly.

Acid-Base Titrations Additional NaOH is added. pH rises as equivalence point is approached.

Acid-Base Titrations Additional NaOH is added. pH increases and then levels off as NaOH is added beyond the equivalence point.

Acetic acid titrated with NaOH Weak acid titrated with a strong base Weak acid titrated with a strong base

The pH Scale Because concentration values may be very small, it is often more convenient to express acidity in terms of pH. Definition of pH pH is defined as the negative logarithm of the molar hydronium-ion concentration. pH = -log [H 3 O + ] often written as : pH = -log [H + ]

Other “p” scales – pOH In the same manner that we defined pH we can also define pOH: pOH = -log [OH - ] pH + pOH = 14.00

Henderson-Hasselbach Equation CH 3 COOH  H + +CH 3 COO -

Problem: Calculate the pH of a solution containing 0.20 M CH 3 COOH and 0.30 M CH 3 COONa Solution: Using the Henderson-Hasselbalch equation and the value of K a for CH 3 COOH = 1.8 x we can find the pH of the solution. pK a = -log K a = -log ( 1.8 x ) = 4.74

Problem: a) What is the pH of a 1.0 L buffer solution containing 1.00M CH 3 COOH and 1.00M CH 3 COONa b) after addition of 0.10 mol gaseous HCl? Solution: Using the Henderson Hasselbalch equation we can calculate the pH of the buffer. a) pH = pK a + log ( [base]/[acid]) = log ( 1.00/1.00) = = 4.74