Sciencemadness Discussion Board

Two unrelated questions: Water hardness and NaOH

Thomas Winwood - 19-11-2005 at 18:28

I live in a hard-water area and as such we have a water filter. Would the water which comes out of this be suitable for performing reactions with, or is there something else which I need to do? Should I construct a still?

Additionally, is it worth my while to buy large quantities of sodium chloride, dissolve it in water and electrolyse it to obtain the hydroxide in bulk?

Darkblade48 - 19-11-2005 at 18:38

I also have hard water in the area where I live, and have a water softener. These things work by exchanging the cations (Ca+2, Mg+2) in the water and replace them with Na+ cations (obviously 2 Na+ for each Ca+2 or Mg+2).

The ions should not interfere with your reactions, unless you really need to have nothing in your water. Then you could always just purchase some distilled water.

In my experience, I've never had the extra sodium cations in my tap water affect my reactions in any way.

Douchermann - 20-11-2005 at 12:23

Yeah, tap water with a water softener would be fine, there is such a small ammount of the Ions in there anyway. For those of you wondering, the salt that goes in the water softener does not actually mix with the water, it washes little beads called zeolite IIRC, these beads transfer the sodium ions into the water and replace the calcium,magnesium and any other ions in there. Every once in a while, the system will wash the beads to remove the other ions and replace them with fresh sodium ions and the cycle repeats.

Twospoons - 20-11-2005 at 13:32

You could also just put a bucket outside when it rains - why pay for distilled water when it falls out of the sky for nothing?

Thomas Winwood - 20-11-2005 at 13:37

Rainwater is slightly acidic (pH 5-6, if memory serves me correctly) and contains sulphate and nitrate ions from careless people emitting sulphur and nitrogen oxides into the air. Not good for chemistry.

Darkblade48 - 20-11-2005 at 14:34

Quote:
Originally posted by Thomas Winwood
Rainwater is slightly acidic (pH 5-6, if memory serves me correctly) and contains sulphate and nitrate ions from careless people emitting sulphur and nitrogen oxides into the air. Not good for chemistry.


Generally true, you especially don't want to collect rain water if you live in major cities where pollution is abundant.

In general, I'd find that the sulfate ions would be more problematic (i.e. form precipitates when you don't want them) rather than the nitrates, as most (I think it's actually all) metal nitrates are soluble.

Twospoons - 20-11-2005 at 18:04

Then again the chlorides in tap water can be problematic too. For me its the Ca and Mg in our incredibly hard tap water that are trouble, especially when making soap.

neutrino - 20-11-2005 at 19:19

Do these ion exchange resins also work for anions?

I, too am cursed with incredibly hard tap water. A single drop of AgNO<sub>3</sub> will make liters of this stuff very cloudy.

evil_lurker - 20-11-2005 at 21:51

Use a reverse osmosis unit with a deionization stage...

I have one and the total dissolved solids is like almost nothing when the water comes out... maybe like 2-3 ppm.