Question

Why glass electrode cannot be used for solution of ph above 9.0?

Answer 1

Glass electrodes are used to measure the pH value of solutions..

Generally Glass Electrodes are not preferred for reading the pH of solution greater 9.0 because it results in Alkaline Error .

Explanation:

⇒Alkaline error occurs when glass electrodes are used to measure pH solution above 9. 

⇒Due to High pH value, the activity of H⁺ ions will be less  and Sodium ions will replace hydrogen ions at outer gel layer of glass electrode and a low pH value is measured.

Answer 2

This is because in case of glass electrodes, above pH of 9 alkalineerror occurs. Alkaline error is a systematic error which occurs when glass electrodes are utilized to read the pH of an highly alkaline solution whose pH is above 9, the electrode starts responding to sodium ions and as a resultgives a pH reading that is consistently very low.