Dear Mamta,

Yes, pH can be less than zero and more than 14. You can see some elaboration on this in Wikipedia.

Best regards,

Orlando

That is really too much to explain here. Try Wikipedia

It is common that the pH scale is argued to range from 0-14 or perhaps 1-14, but neither is correct. The pH range does not have an upper nor lower bound, since as defined above, the pH is an indication of concentration of H+. For example, at a pH of zero the hydronium ion concentration is one molar, while at pH 14 the hydroxide ion concentration is one molar. Typically the concentrations of H+ in water in most solutions fall between a range of 1 M (pH=0) and 10-14 M (pH=14). Hence a range of 0 to 14 provides sensible (but not absolute) "bookends" for the scale. One can go somewhat below zero and somewhat above 14 in water, because the concentrations of hydronium ions or hydroxide ions can exceed one molar.

Thanks yamini.

It can apparently be negative. See Article Negative pH Does Exist

Dear Mamta,

Yes, pH can be less than zero and more than 14. You can see some elaboration on this in Wikipedia.

Best regards,

Orlando

Yes

Can you explain a bit further. What negative pH actually means.@Alan F Rawle

If you understand the definition of pH then everything follows from that. Take a look at: https://www.thoughtco.com/is-a-negative-ph-possible-603653

Dear Michal Kordač, your comment about the limits of pH (0 and 14) and how theses would vary if the temperature and the solvent are changed, is something that I have reflected on other occasions: What would be the situation of the pH measurements with another solvent? Should we adjust the concepts we know on the subject?

The pH is a concept that is closely linked to the autoionization of water (2H2O H3O+ + OH-), as you point out elsewhere in your comment. Suppose, that the water is replaced by pure methanol (one of the hydrogens in the water is replaced by a -CH3 group), the autoionization of methanol would be

CH3OH + CH3OH CH3OH2+ + CH3O-

In what extension does this process occur? Is the constant of this equilibrium higher or lower than that of water at the same temperature? Would conventional glass electrodes for measuring pH respond appropriately to the species CH3OH2+?

By the way, pH measurements close to 14 or above this value, face a practical problem: the alkaline error. A limitation experienced by special glass membranes containing pH electrodes leads to lower false pH measurements. This is mainly due to the fact that these membranes are sensitive to other cations (Na+ or K+, for example) at high alkalinity.

At high alkaline pH (> 12) then soda lime glass will slowly dissolve.

The pH electrodes also experience the acid error, in this case the readings are falsely higher (it could happen that a negative value measured experimentally is actually more negative). However this problem appears in the vicinity of readings of 1. On the contrary, the alkaline error appears faster, in some type of glass membranes could occur from 10. When buying glass electrodes is a variable that should be considered. Electrodes with alkaline and acid errors lower may be more expensive.

Dear Alan F Rawle , a limitation more associated with the measurement of extreme pH and a reason to reprimand careless students who leave the electrode sleeping in very alkaline solutions.

Titration as a measure of OH- may be more appropriate in highly alkaline media.

Will electrode manufacturers not be making innovations with new materials to overcome these disadvantages of glass?

Yes-yes, dut it dépense of the environment7

@ Mamta Thakur

Yes. Please have a look at the following useful links.

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1488&context=usgsstaffpub

https://www.sciencefocus.com/science/could-a-ph-greater-than-14-exist/

https://www.quora.com/Can-pH-be-negative-or-higher-than-14

Thanks!