Need help with easy chemistry :)

[jammon]

hey there... I was wondering if anyone could help me with 3 questions:

1) Without pH papers, is there a way to calculate the pH of a H2SO4 (sulfuric acid) solution knowing the concentration is 5% ?

2) If a non-polar solvent such as Hexane is miscible with Ethanol 96°, does that mean that they mix completely? If so, would the water traces from the alcohol stay at the bottom below the Hexane layer?

3) H202 (Hydrogen peroxide) is an oxidizing agent just like Permanganate. Is it possible to dilute or concentrate Peroxide in order to make it work like Permanganate?
Besides the potency of them, what else differs?

 

[23536]

Um, your third question is sort of synth discussion, isn't it?

#2 is a good question!

And oh yeah, the answer to #1 is yes.

 

[jammon]

You are a moderator? You belong to drugs-forum. There they're just like you. Pretty much useless
Love this site though, thanks a bunch anyways

 

[Hammilton]

three is a qualified yes. depends what you're trying to do. and beyond that, we're into synth territory.

 

[23536]

You are a moderator? You belong to drugs-forum. There they're just like you. Pretty much useless

Hey I answered your first question

edit ok fine, if 5% is by mass, then there's 50 grams sulfuric acid per liter. Molecular weight of H2SO4 98 g/mol, so 50/98 = 0.51 moles H2SO4 per liter solution. That's an H+ molarity of 0.51, so pH = -log[0.51] = 0.29

I think.

 

[jammon]

Lol. Thanks :D
Though I don't think it's 0.29. Too low,man. Should be around 5. I thought it'd be easy to calculate ph from the concentration :S
and I've asked on many forums. but thanks anyways
And yeah I guess I'm gonna have to look for Permanganate, since nobody seems to know how to replace it with Peroxide, either, :S

And yeah, they use permanganate to make those lovely drugs the DEA craves for, but I wish I could find some real and honest chemist online

 

[Roger&Me]

hey there... I was wondering if anyone could help me with 3 questions:

1) Without pH papers, is there a way to calculate the pH of a H2SO4 (sulfuric acid) solution knowing the concentration is 5%

Here's a post I made in a DMT extraction thread about calculating pH, you can work it out from this. Start by converting to molarity (mols/L of soln), calculate [H+] rather than [OH-] but the same logic applies. I loathe any type of numerical calculations, so I would personally just buy the stupid pH papers. :D

Essentially, first you work out the concentration of OH- in your solution. NaOH has a molar mass of roughly 40g/mol, so you can work out the molarity of your solution using that value. Molarity is number of moles of solute per liter of solution. You just have to know how many grams of NaOH you added to how many liters of solution, and using molar mass you can calculate the solution's molarity.

[X]="concentration of X", expressed here in mols/Lsoln

Since there's 1 OH- for every NaOH, its a 1:1 ratio, so [OH-] = [NaOH]

Let's assume for hypothetical purposes that your NaOH solution [OH-] turns out to be 2.9 x 10^-4 M. I just pulled this number out of my ass arbitrarily for example purposes, mind.

pOH = -log[OH-] = -log(2.9x10^-4) = 3.54

Since this is pOH, and we want pH, we need to consider that pH+pOH=14.00

pH + pOH = 14.00
pH = 14.00 - pOH
pH = 14.00 - 3.54 = 10.46

The final answer shows that the solution is basic (pH > 7), which is consistent with an NaOH solution. Always ask yourself, "does this answer sound reasonable?" In this case, it does.

Alternatively, you can use the ion-product constant of water, Kw=[H+][OH-]=1.0x10^14, to calculate [H+], and then you can calculate the pH from the [H+].

Some useful relationships regarding pH:

Kw=[H+][OH-]=1.0x10^-14

pH=-log[H+]

pOH=-log[OH-]

pH+pOH=14

[H+]=10^-pH

Also:

Hey I answered your first question

edit ok fine, if 5% is by mass, then there's 50 grams sulfuric acid per liter. Molecular weight of H2SO4 98 g/mol, so 50/98 = 0.51 moles H2SO4 per liter solution. That's an H+ molarity of 0.51

H2SO4 is a diprotic acid, so it can donate 2 protons per molecule. Concentration of H+ is 2x the concentration of H2SO4.

 

[23536]

H2SO4 is a diprotic acid, so it can donate 2 protons per molecule. Concentration of H+ is 2x the concentration of H2SO4.

Only the first ionization is complete with sulfuric acid.

 

[i are spectre]

you need pka values of both h2so4 and hso4 then add them up. you can assume its a strong acid though and youll get a close enough ph. gotta convert 5% h2so4 to molarity.

-log[M] = pH, where M is molarity.

*edit yup its 0.29

 

[jammon]

so? whats the pH of 5% sulfuric acid? It's not 0.29, that would kill these precious gems I'm about to extract
Come on man, all I need is some chemist to tell me the pH, and then I get the pH paper and make diluted solutions dropwise until the pH is...
And I wonder... since 5% is pretty much around pH 3 or 5, 10% should be close to 0 and 1% would be like almost neutral pH, I suppose.
thx for the input

 

[shishigami]

Not even calculating anything I can certainly say it's less than ph 1. Even though it's diprotic the Ka of HSO4- is too low to make a significant difference in the pH.

For the second question I would assume that the H2O would not drop out form another layer with the EtOH/Hexane solution.

Oxidizers have different uses depending on the situation being used. I doubt that H2O2 would be an adequate substitute for what ever reaction you have that calls for MnO4-.

 

[Coolwhip]

And I wonder... since 5% is pretty much around pH 3 or 5, 10% should be close to 0 and 1% would be like almost neutral pH, I suppose.
thx for the input

Don't forget that pH is logarithmic, and don't you need to be calculating it at equilibrium since only the first dissociation is mostly completed, so Ka(2) = [SO4^2-]*[H+]/[HSO4^-] or HSO4- + H2O <--> H+ + SO2 for something like H2SO4 + H2O --> H+ + HSO4- + H20 <--> SO4^2-

And I'm no chemist but .29 does seem low...I mean battery acid is what ~0.5 pH? And surely it's got a heck of a lot more sulfuric acid in it than 5%.

edit: or is it -0.5? and that we just can't easily measure pH that low and have to rely on the calcs?

 

[Pomzazed]

5% sulfuric acid in water is pH 0.29

 

[23536]

And yeah I guess I'm gonna have to look for Permanganate, since nobody seems to know how to replace it with Peroxide, either, :S

And yeah, they use permanganate to make those lovely drugs the DEA craves for, but I wish I could find some real and honest chemist online

I think the H2O2 question is really interesting and would love to hear an explanation; but regarding its utility in organic synthesis, you can't discuss it on Bluelight.

 

[Indole]

so? whats the pH of 5% sulfuric acid? It's not 0.29, that would kill these precious gems I'm about to extract
Come on man, all I need is some chemist to tell me the pH, and then I get the pH paper and make diluted solutions dropwise until the pH is...
And I wonder... since 5% is pretty much around pH 3 or 5, 10% should be close to 0 and 1% would be like almost neutral pH, I suppose.
thx for the input

The pH has been calculated 3 times for you so far. If .29 is not the pH you are looking for, then you need to make changes to your solution to adjust the pH. And frankly, if you can't calculate a pH value from concentration and pKa, you shouldn't be doing anything chemistry related.

 

[jammon]

first of all ,that last post saying ' you shouldn't be doing anything chemistry related.'
you can shove that up your %#".
And the one before saying 'but regarding its utility in organic synthesis, you can't discuss it on Bluelight.'
that is just plain hypocrisy. This is a drug forum, man. You do drugs, and I bet some of them are synthesized, probably LSD, meth and E.
What the fuck?
Nevertheless, I aint synthesizing something right now, just getting some precious alkaloids out of some tea, no big deal.
Anyways, the pH I'm looking for is 5.
thank u all

 

[shishigami]

Synthesis can't be discussed because it could get the forum as a whole into legal trouble. Synthetic drugs can be discussed.

If you want a pH of 5 dilute your 5% H2SO4 by about 50,000 times.

 

[jammon]

Talking about Sulfuric Acid doesn't necessarily suggest I'm synthesizing drugs, 8).
Dunno if it's 5% what I've got. Guess I'm gonna make solutions dropwise till pH 5.
And what about question 2? That one I find interesting... plain curiosity

 

[Pomzazed]

#0 People said that, due the the Bluelight rule prohibit talking about synthesis-related things, dont be so rude to them. Its just a friendly notification of forum guideline.
#1 pH=0.29 as stated
#2 If there is only trace of water then it wont appear anywhere. water in organic solvents from tiny droplets (emulsion) dispersed throuhout the solution, the more water, the more the solution change from clear to 'turbid' look. Unless there are enough water contamination then it comes out as visible droplet. That is why organic chemists use drying agents like anhydrous Na2SO4 or MgSO4 or CaCl2 or molecular sieve to dry their solvent.
#3 Cannot be directly compared, as it goes via different mechanism.

 

[jammon]

thank you very much
It's very weird that the text I read calls for a solution with pH 0.29, it would destroy the alkaloid.
thanks a lot