Identifying if Liquid on Table is Water

[darkar]

I assume that all of us drink water everyday. But now, i found a cup of liquid on my table. I wonder if it is really water or not. So, what should i do to identify this is water if:
a) i want to drink it if i find it is water.
b) only identify it.

 

[Crumbles]

I assume that all of us drink water everyday. But now, i found a cup of liquid on my table. I wonder if it is really water or not. So, what should i do to identify this is water if:
a) i want to drink it if i find it is water.
b) only identify it.

This is only my guess at how you can find out! Don't hold me responsible if you end up drinking anything other than water!

(a) Take a sample and see if it boils at 100C when at a pressure of 1atm. If it boils at exactly at 100C, it is pure water! If it boils at a slightly higher temp it could still be water but with impurities. You can also monitor the melting point of the liquid. If the melting point is exactly 0C, you can conclude it is water, and if it melts at a temperature slightly lower than 0C, it could still be water but with impurities.

(b) Put in some dehydrated Copper Sulphate crystals and if the crystals turn blue, you've got water in the cup. But mind, this could also mean that you have water + other things. This test only says that the liquid consists of water.

You could also do a fractional distillation of the liquid and separate all the constituents if it does have many constituents.

 

[kuenmao]

If you only want to identify it, use dry cobalt(II) chloride. It'll change from blue to pink. But same as using copper(II) sulphate, you only know that you've got water in the cup. If you want to find out whether it is pure, you better use the "melting point and boiling point" test.
If you want to drink it...just use a dropper or something to take a small sample while leaving the rest untouched.

 

[Gonzolo]

(a) Take a sample and see if it boils at 100C when at a pressure of 1atm. If it boils at exactly at 100C, it is pure water!

Collect the vapor while you do this, wait for it to cool, and drink!

Gonzolo is not responsible for sickness or death if this doesn't work for some reason.

 

[arildno]

Just a question here:
Is it actually proven that there cannot exist another liquid than water which has the same melting/boiling temperatures?

 

[russ_watters]

Just a question here:
Is it actually proven that there cannot exist another liquid than water which has the same melting/boiling temperatures?

Certainly there can exist another liquid with the same melting or boiling point (both at the same time would be unlikely, but still possible).

 

[arildno]

So, you cannot conclude from these experiments that what you have in front of you is water..

 

[pervect]

I assume that all of us drink water everyday. But now, i found a cup of liquid on my table. I wonder if it is really water or not. So, what should i do to identify this is water if:
a) i want to drink it if i find it is water.
b) only identify it.

Well, if you put it through a mass spectrometer, and only get O & H, and an IR spectrometer, an only see the absorption frequencies associated with water (and not those associated with hydrogen peroxide), you can probably be pretty sure it's water.

To be extra safe, give some of it to a lab animal first, and wait for a few weeks to make sure it stays healthy.

 

[russ_watters]

So, you cannot conclude from these experiments that what you have in front of you is water..

In science, you can never conclude anything with absolute certainty.

 

[arildno]

Well, we always have the "if it walks like a duck, quacks like a duck, it's probably a duck and not some limpwristed TRex"-argument at our disposal.
I'll guess we have to be satisfied with that.

 

[Nenad]

water doesn't boil at 100 degrees. Its a little less.

 

[Crumbles]

water doesn't boil at 100 degrees. Its a little less.

What makes you say this?? In fact the exact temperature at which water boils depends on what the atmospheric pressure is. And this is something that varies from day to day and is different at various altitudes. So what are you basing yourself on when saying water boils below 100C?

http://www.fetco.com/boilingpoint.htm

 

[pallidin]

Vodka looks an aweful lot like water. If you suspect it as such, send it my way and I will personally examine the issue, though sample return is not gaurenteed :)

In all reality, without the use of chemistry/physics devices I suppose your issue is unsolvable. But IN reality, most animals have the ability to detect water through the senses available(first odor, then taste). After all, water is necessary for most animal life, thus you have been given the ability to discern it. Your brain works out the details.

 

[Nenad]

What makes you say this?? In fact the exact temperature at which water boils depends on what the atmospheric pressure is. And this is something that varies from day to day and is different at various altitudes. So what are you basing yourself on when saying water boils below 100C?

http://www.fetco.com/boilingpoint.htm

you just said it yourself, water boils at different temperatires at different pressures. At STP, water boils at something like 99.7 degrees.

 

[Integral]

you just said it yourself, water boils at different temperatires at different pressures. At STP, water boils at something like 99.7 degrees.

Please post a reference? According to my 53rd edition of the CRC handbook of Chemistry and Physics water boils at 100C at 1atm (760mm Hg). Since this is the definition of the boiling point of water I do not see how it could be anything else. A boiling point of 99.7C corresponds to a pressure of 751.9 mmHg

 

[Crumbles]

you just said it yourself, water boils at different temperatires at different pressures. At STP, water boils at something like 99.7 degrees.

Hmm, can you please tell us where you got this figure from? And if you are speaking in terms of the Celsius Temperature Scale, that surely can't be right because of the way the scale is defined/calibrated itself.

"The zero point of the Celsius scale is set to the temperature at which water freezes. The number 100 is set to the temperature at which water boils. Celsius set 100 equal divisions (degrees) between the freezing and boiling points."

http://www.windows.ucar.edu/earth/Atmosphere/temperature/celsius.html