i was given water samples to test for a chemistry assessment and i didnt find any anions or cations!! i did all the tests how we had done in class. did i do something wrong? its not possible that creek and tap and fresh water have none, is it?? also i now have to write this up as a prac and i cant find any pointers on the internet on how to do it correctly. any help would be much appreciated!!! thanks...
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Water testing (1 Viewer)
- Thread starter gunshop
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It depends a bit on what anions you were testing for, but there shouldn't be that much in the way of easily detected ions in fresh (creek or tap) water that is unpoluuted, except that chloride should be detectable in tap water. If it isn't, add a bit more silver(I) nitrate solution, but I'd be surprised if tap water didn't have detectable chloride. PS: If you are looking for chloride, get two equal samples in test tubes of the same size, and add the silver(I) nitrate. Then, look directly down the test tubes through the solution onto a black surface. This is the easiest way to spot the cloudiness caused by a small amount of silver(I) chloride formation.
thanks. i figured chlorine would be there. maybe i just wasnt looking hard enough!! but what about cations? the thing is i dont know what theyre looking for in the prac. other than the obvious.
like, how do i say that i got no cations, why? shouldnt i be able to justify it? i dont know much about it as we havent finished most of the topic yet. but if the creek water had a bitter smell and was full of sticks until it was filtered, then shouldnt it have cations or anions?? so do i say my tests werent reliable or whatever becuase i didnt find anything or do i say there shoudlnt have been anything because of whatever reasons...
like, how do i say that i got no cations, why? shouldnt i be able to justify it? i dont know much about it as we havent finished most of the topic yet. but if the creek water had a bitter smell and was full of sticks until it was filtered, then shouldnt it have cations or anions?? so do i say my tests werent reliable or whatever becuase i didnt find anything or do i say there shoudlnt have been anything because of whatever reasons...
Firstly, be careful with your terminology - it's the chloride ion, Cl<sup>-</sup>, not chlorine, which implies the substance Cl<sub>2</sub>.
Secondly, if there are anioins present, then there must be cations to balance the charge. There could be a number present that are below the detection levels of the techniques that you are using. Alternately, there could be cations present that you are not testing for - like the sodim ion, Na<sup>+</sup>. With tap water, you could look at what Sydney Water adds to tap water, and what it removes, to give you some more evidence to discuss. Certainly, there should be fluoride present.
Did you test the pH? That would give you evidence of levels of hydroxide / hydronium. I would guess the samples would be slightly acidic, due to dissolved CO<sub>2</sub>, which means you could also discuss the formation of the hydrogencarbonate ion.
A test with sulfide would tell you whether there were detctable heavy metals present, too.
Note that a negative result does not necessarily imply a problem with accuracy or reliability. The test for phosphate (say) may accurately and reliably provide no evidence for the presence of phosphate. This does not mean that there are no anions present, nor does it even mean that there is no phosphate present. It does mean that there is no detectable phosphate present, and thus the amount that is present must be below the detection limit of the technique - this includes the possibility that there is none, but you can only say with any certainty that any amount present is less than can be detected.
Secondly, if there are anioins present, then there must be cations to balance the charge. There could be a number present that are below the detection levels of the techniques that you are using. Alternately, there could be cations present that you are not testing for - like the sodim ion, Na<sup>+</sup>. With tap water, you could look at what Sydney Water adds to tap water, and what it removes, to give you some more evidence to discuss. Certainly, there should be fluoride present.
Did you test the pH? That would give you evidence of levels of hydroxide / hydronium. I would guess the samples would be slightly acidic, due to dissolved CO<sub>2</sub>, which means you could also discuss the formation of the hydrogencarbonate ion.
A test with sulfide would tell you whether there were detctable heavy metals present, too.
Note that a negative result does not necessarily imply a problem with accuracy or reliability. The test for phosphate (say) may accurately and reliably provide no evidence for the presence of phosphate. This does not mean that there are no anions present, nor does it even mean that there is no phosphate present. It does mean that there is no detectable phosphate present, and thus the amount that is present must be below the detection limit of the technique - this includes the possibility that there is none, but you can only say with any certainty that any amount present is less than can be detected.