[superglue_999]

Hi there,
Could you please help me with the following problem:

I would like to have a table for the following acids pH (or Ka acidity constant)
HX(cl,br,i,f), hno3, h2s, h2so4(2 values, also for hso4-), r-cooh in general, hcn, nh4, Ar-oh(fenols), R-oh (alcohols) , and water (which i think it is situated between alcohols and fenols)

besides this, i also have some questions, i hope you can help me:
1.
if we have a reaction betwenn sulfuric acid and water, it`s an exotermic one, why do we hace to cool it to improove the reaction, because if we have a higher temperature that means the molecules will hit harder and react more.
i know this is the oppesite of an endotermic reaction, that if we heat it than will reac better, giving energy for breaking the bonds, but i can`t figure it out for the exotermic one.

2.
do ionic compounds (such as salts) solvate in alcohols? (if not, why only in water)

3.
what happens with the co2 from mineral water if we cool it under 0 degrees celsius, regarding the solubility of co2 (rises, lowers, the same?)   

4.
a supersaturated solution means that in a solution we have more substance (e.g. NaCl) than the solution (e.g. H2O) can solvate

5.
could ytou please tell me where can I fiind some good articles about acids\bases OR about the solubility of substances and what ifluences it



thank you
please excuse my spelling errors

[Borek]

I would like to have a table for the following acids pH (or Ka acidity constant)

Check pKa values link on the left.

[shelanachium]

A few answers:

1.Adding sulfuric acid to water is exothermic. VERY exothermic. You cool the mixture to stop it blowing up in your face. It is not done to speed up the reaction, that's the last thing you want!

2. Ionic compounds in alcohols. Indeed some do dissolve, but usually not as easily as in water. Water dissolves many ionic compounds because it is itself highly polar, the bent H2O molecule has a positive end, the H atoms, which are attracted to the negative ions (anions), so the water molecules surround them with the H atoms next to the anion. The O end is negative, so the water molecules surround the positive ions (cations) with O facing them.

Alcohols contain a polar O-H bond like water, but only one rather than two. The C-O bond in alcohols is also polar, but the attached organic group such as C2H5 (in ethanol) is much larger than a hydrogen atom so the positive charge in it is less concentrated, and its attraction to negative ions much less.

So alcohols do not dissolve ionic compounds as effectively as does water.

3 CO2 in frozen mineral water. Gases in solution normally come out when the liquid is frozen. This is why you get bubbles in ice-cubes - they are the air that was dissolved in the water before it froze.

Gases come out on freezing because crystalline solids have regular structures into which alien molecules like those of dissolved gases will not fit.

In some cases gases CAN fit into ice-crystals, but then the ice assumes a different structure based on dodecahedra, which have cavities inside in which small gas molecules like CO2 and also methane CH4 will fit. Look up 'Gas Hydrates' on Google.

4 Supersaturation. Some solutions can indeed hold more of a compound than would normally dissolve. As most substances are more soluble in hot solvents than cold ones, supersaturated solutions can sometimes be obtained by cooling a hot solution. Best-known example is sodium thiosulfate Na2S2O3. Add a tiny piece of solid sodium thiosulfate to a supersaturated solution and it crystallises at once.

Why does this happen? Because in order to crystallise some molecules need to be 'taught' how to arrange themselves, by a piece of crystal already assembled or by a crystal of very similar structure. Until such a template comes along, the substance remains in solution.

[superglue_999]

thank you for the answers!