chemistry: collecting gases

anpanman SG

can someone suggest to me an experiment on how you can remove traces of hydrogen chloride from an oxygen supply? i think we can dissolve the gas since hydrogen chloride is soluble in wawter while O2 is slightly soluble before heating it and collect it using the downward delivery method. does anyone of you have a better way of retrieving hydrogen chloride gas? if yes, do enlighten me. Many thanks. :)

Garrick_3658 SG

HCl is an acidic gas, so why not use an alkali to remove it to achieve neutralisation?

anpanman SG

HCl is an acidic gas, so why not use an alkali to remove it to achieve neutralisation?

but the thing is how do you collect it without it being made impure?

Garrick_3658 SG

Bubble both gases into an alkali for example, NaOH. The HCl gas will react with NaOH (or the other way round if you like) while oxygen, a neutral oxide, will not react with NaOH.

Or you can dissolve it in water if you like.

UltimaOnline SG

If the objective is only to remove HCl(g) from O2(g) (ie. you don't care what happens to HCl(g), this is NOT a separation question in which you have to obtain pure samples of BOTH HCl(g) and O2(g)), then bubbling this gas mixture into water will suffice. HCl will dissociate to ionize in water forming H+(aq) and Cl-(aq), aka hydrochloric acid, leaving the largely insoluble oxygen gas to be collected.

If the question specified dry oxygen gas, then you would bubble the wet oxygen gas (ie. wet because you first bubbled the gas mixture into water to get rid of the HCl(g)) into concentrated sulfuric acid, before collecting the dried oxygen gas in a gas syringe.

anpanman SG

Ok, understood. So that means no heating is required and all? You simply collect the oxygen gas to separate it from the hydrogen chloride gas? I always thought when it says REMOVE HCl(g) from O2 means you have to take out the hydrogen chloride gas, leaving behind the O2 gas. May I know whether it works both ways? Thank You.

I have a question to pose for everyone here.

Let's say an aqueous solution contains a mixture of the salts potassium chloride and copper(II) sulphate. to test for presence of Cl- ions, you add HNO3 followed by Ag(NO)3, resulting in the formation of a white precipitate(silver chloride in this case). how do you write the equation for this reaction?

i wrote something like:

HNO3 + Cl- -> HCl + NO3-

HCl + AgNO3 -> AgCl + HNO3

A little confused by this, simply because I do not understand whether I should include the NO3- ion in the first equation since I do not know the cation of the salt. What is the purpose of adding acid, may I ask.

Please do advise.

Cheers!

UltimaOnline SG

I have a question to pose for everyone here.

i wrote something like:

HNO3 + Cl- -> HCl + NO3-

HCl + AgNO3 -> AgCl + HNO3

Please do advise.

Cheers!

>>> I always thought when it says REMOVE HCl(g) from O2 means you have to take out the hydrogen chloride gas, leaving behind the O2 gas. <<<

That's what I said.

(HCl + O2) - HCl = O2

And to remove HCl, bubble the mixture (of HCl + O2) into water. Then what's left (in gaseous state), is simply O2.

Why would heating need to be involved?

>>> Let's say an aqueous solution contains a mixture of the salts potassium chloride and copper(II) sulphate. to test for presence of Cl- ions, you add HNO3 followed by Ag(NO)3, resulting in the formation of a white precipitate(silver chloride in this case). how do you write the equation for this reaction? <<<

Ag+(aq) + Cl-(aq) --> AgCl(s)

>>> What is the purpose of adding acid, may I ask. <<<

I've written this question and the solution here on my "Collection of Chem Qns" thread below.

Find (control-F) "acidify silver nitrate"

http://www.sgforums.com/forums/2297/topics/320107

Garrick_3658 SG

You don't have to include the acid in the ionic equation.

You add the acid to remove carbonate impurities so that no carbonate precipitates will be formed.

anpanman SG

thanks everyone!

davidche SG

add acid to remove possiblity of hydroxide, carbonate.