[Twigg]

This is not a textbook question. I dissolved 0.34g copper sulfate pentahydrate and 1.61g calcium chloride (not sure of the hydrate formula, obtained it as road salt but it had been left out) in 10mL of water in a plastic test tube hoping to isolate (more or less) CuCl2 so I could determine it's color at a given concentration. I got some yellow/green solid trapped under the excess solids and white precipitate (CaSO4, I expect), and a milky blue solution. However, I also got a bunch of clear gas bubbling out. This was in a closed test tube, and the reaction was endothermic (I felt it got colder, initial temp was 24.5*C), so Henry's Law might explain it in terms of a decrease in the air pressure inside the test tube. That's the most elegant and convenient solution I can come up with. I also took the pH of the resulting solution with a piece of litmus paper. I don't really trust a litmus paper pH test, but it indicated a pH of 5. Also, when I mixed up the contents, the greenish solid settled beneath the blue, so I expect it had a density greater than copper sulfate.

To reduce the problem a bit, I can fill in as much as I know about the chemical reaction in pieces:

1. CuSO₄_5H₂O (s) <-> Cu²⁺ (aq) + SO₄^2- (aq)
2. CaCl₂_?H₂O (s) -> Ca²⁺ (aq) + 2Cl^- (aq)
3. Ca²⁺ (aq) + SO₄^2- (aq) (<)-> CaSO₄ (s)
4. Cu²⁺ (aq) + 2Cl^- (aq) (<)-> CuCl₂ (s)
5. (unknown reactants) (<)-> ? (gas)

To reduce it even further, here's the complete break-down:

Chemical Species and Total Amounts Before Reaction:
Ca²⁺ (aq), >7.33E(-3) mol
Cl^- (aq), >1.47E(-2) mol
Cu²⁺ (aq), <1.38E(-3) mol
SO₄^2-, <1.38E(-3) mol
H₂O (l), ~0.555 mol
H⁺ (aq), 10^-7 mol
OH^- (aq), 10^-11 mol

Any ideas? What gases can you hypothetically get from that?

[vmelkon]

I had tested my road salt, Windsor brand, by adding NaHCO3. If there was CaCl2, it would have given

2 NaHCO3(aq) + CaCl2(aq) => 2 NaCl(aq) + CaCO3(s) + H2O(l) + CO2(g)

but nothing happened. This is probably el-cheapo sea salt.

I know some of the more expensive brands can have CaCl2 or MgCl2 or urea or uric acid and blue specs.
Test your gas with a Ca(OH)2 solution.

[Twigg]

@vmelkon, thanks for the suggestions!

I'm pretty confident the road salt is CaCl2 based on the crystal shape (described in the CRC as white hexagonal crystals, which is exactly what I have). More importantly, I just did the test you mentioned for the road salt with positive results. The mixture immediately starting fizzing and bubbling and turned cloudy and milky white. It's almost definitely CaCl2. Litmus test says the final solution was pH neutral too. I can get the mass of the precipitate later to figure out the hydrate formula if needed.

I've never tested for carbon dioxide with limewater before. I only have a few grams of the solid. What's a good concentration and volume to use? I probably have less than two grams, and I'll only make some up from sodium hydroxide as a last resort. One other question, I'm stuck with tap water for my solutions. Is the dissolved carbon dioxide going to mess up the test?

Also, I just took another look at the contents of that tube (it's been sitting for several hours now), and the mixture of solids at the bottom of the tube has changed. Now there's no green, only copper sulfate blue and a thin layer of aqua or something (looks more like wet copper carbonate, but not as distinctly greenish). I'm not great at describing the colors, but I have clear pictures of the reaction mixture now and from before if you need them.

[4js]

Not able to help So complicated

[vmelkon]

Ca(OH)2 doesn't dissolve much in water. Just put some water in a test tube and a small spatula of Ca(OH)2 and shake. Wait for any solids to settle. Then bubble the gas through it. It should turn milky quickly since CaCO3 solubility is lower than Ca(OH)2.