why a solution showing ph value 7 need not necessarily be water?
Answers
Answered by
1
Are all aqueous solutions with pH=7 called water?
As others have mentioned, there are innumerable aqueous solutions which could have pH=7.0 at 25C, none of which you could reasonably call 'water'.
Of those liquids we would reasonably call 'water', only pure H2O at 25C will have a pH of 7.0 For this to occur, the water must be ultra pure and free from dissolved solids, liquids or gases. Which means that most of what we call 'water' on (and within) the planet does not have a pH of 7.0 at 25C.
Rainwater is naturally slightly acidic (pH of ~5.5 at 25C )... due to dissolved CO2 and the formation of H+ and HCO3- ions. (Just 0.22 ppm CO2 dissolved in pure water will cause the pH to go from 7.0 to 5.0)
Seawater on the other is slightly basic, having a pH of 7.5 to 8.4 at 25C)... due mainly to dissolved carbonate / bicarbonate ions which originate primarily from calcite-rich marine sediments.
River water and ground water generally range from a pH of 6.5 to 8.5 at 25C, depending on the type of dissolved salts they contain, which are due largely to the type of soil and minerals in its catchment as well as the minerals in the rock through which the river cuts.
Freshly distilled water is not even at pH 7.0 because, just like rain water, it absorbs CO2 from the atmosphere as soon as it condenses and runs into its storage container. Freshly distilled water usually has a pH of about 6.0 at 25C, unless vacuum distilled and stored in airtight containers. Even then the composition of the container may eventually change the pH as small amounts of contaminants dissolve in the water. Bacterial contamination can also slowly change the pH.
Pure water with a pH of exactly 7.0 is therefore not easy to produce, nor is that pH easy to maintain
is right, of course, although it's not uncommon in a lab to hear something like, "Don't worry, that's non-haz. I titrated it, so it's just saltwater now."
Obviously this isn't always the case, some salts are hazardous, but it's a fairly common refrain nonetheless. So informally, yes, but technically no, a pH 7 solution of (for example) ammonium sulfate would not be referred to as "water."
Log of Hydrogen Ion concentration in Water.
So, if there is no water , then there will be no pH. That is why 100% acids doesnt show any pH. I have tried it with Oleum (Fuming sulfuric acid), Fuming Red Nitric acid and 100% pure Triflouoroacetic acid. the pH meter shows -2 pH, which is not possible.
(if it helps please mark BRAINLIEST
As others have mentioned, there are innumerable aqueous solutions which could have pH=7.0 at 25C, none of which you could reasonably call 'water'.
Of those liquids we would reasonably call 'water', only pure H2O at 25C will have a pH of 7.0 For this to occur, the water must be ultra pure and free from dissolved solids, liquids or gases. Which means that most of what we call 'water' on (and within) the planet does not have a pH of 7.0 at 25C.
Rainwater is naturally slightly acidic (pH of ~5.5 at 25C )... due to dissolved CO2 and the formation of H+ and HCO3- ions. (Just 0.22 ppm CO2 dissolved in pure water will cause the pH to go from 7.0 to 5.0)
Seawater on the other is slightly basic, having a pH of 7.5 to 8.4 at 25C)... due mainly to dissolved carbonate / bicarbonate ions which originate primarily from calcite-rich marine sediments.
River water and ground water generally range from a pH of 6.5 to 8.5 at 25C, depending on the type of dissolved salts they contain, which are due largely to the type of soil and minerals in its catchment as well as the minerals in the rock through which the river cuts.
Freshly distilled water is not even at pH 7.0 because, just like rain water, it absorbs CO2 from the atmosphere as soon as it condenses and runs into its storage container. Freshly distilled water usually has a pH of about 6.0 at 25C, unless vacuum distilled and stored in airtight containers. Even then the composition of the container may eventually change the pH as small amounts of contaminants dissolve in the water. Bacterial contamination can also slowly change the pH.
Pure water with a pH of exactly 7.0 is therefore not easy to produce, nor is that pH easy to maintain
is right, of course, although it's not uncommon in a lab to hear something like, "Don't worry, that's non-haz. I titrated it, so it's just saltwater now."
Obviously this isn't always the case, some salts are hazardous, but it's a fairly common refrain nonetheless. So informally, yes, but technically no, a pH 7 solution of (for example) ammonium sulfate would not be referred to as "water."
Log of Hydrogen Ion concentration in Water.
So, if there is no water , then there will be no pH. That is why 100% acids doesnt show any pH. I have tried it with Oleum (Fuming sulfuric acid), Fuming Red Nitric acid and 100% pure Triflouoroacetic acid. the pH meter shows -2 pH, which is not possible.
(if it helps please mark BRAINLIEST
Shruti033:
thanks a lot...
Similar questions