chlorine water preperation - displacment of halogens

There is some chlorine water prepared by the former lab technician that looks transparent. I guess it has expired, because it has to look pale yellow-green (in fact, it is advised to prepare it just before the practical).

Any advice will be highly appreciated. :)
Cautiously smell it. If you can still smell chlorine it should work, but if it's been hanging around a while it won't have an odour and won't work.
 
There is some chlorine water prepared by the former lab technician that looks transparent. I guess it has expired, because it has to look pale yellow-green (in fact, it is advised to prepare it just before the practical).

They say that, but actually to be visibly yellow-green it needs to be ridiculously concentrated. It works for the practicals at far lower concentrations.
 
I always used to make the chlorine using the Pot permang and conc HCl method and then bubble that through water but since finding out about the half a milton tablet in water method, I don't use anything else now. Perfect for displacement reactions and a piece of p...., cake, to set up. :D
 
Hi there,

I need to prepare chlorine water for the displacement of halogens practical. I have read that there are several ways of preparing it. Provided that we neither have sodium chlorate nor chlorine gas, I will follow Michael Clee's recipe. I need about 200 ml (1 bottle of 50 ml x 4 tables) so I will first put 40 ml of bleach, top the bottle up with tap water, then add a few drops of 1M HCl until it turns greenish. I will do this in a fume cupboard, although students will manipulate it in the classroom.

There is some chlorine water prepared by the former lab technician that looks transparent. I guess it has expired, because it has to look pale yellow-green (in fact, it is advised to prepare it just before the practical).

Any advice will be highly appreciated. :)
I made fresh chlorine water and kept diluting it until it was still doable for a halogens test and it was completely clear by the time it as diluted and while I stored it in a screw top bottle it is still lasting me three weeks so far
 
I put 10ml of cheap bleach in a reagent bottle then top the bottle up with tap water. I then slowly pour in some 1M HCl until it starts to turn green. It works a treat for the displacement of halogens experiment. When it starts to go off i just pipette in a bit of bleach/acid until it turns back green. Do this inside a fume cupboard for obvious reasons.
how do you know the stregnth of this method?
 

CovTech

Lvl 38 Alchemist
COMMITTEE
You don't but then again if it works do you really need to?
Yes we do

CLEAPSS give a strength which is appropriate for use in halogen displacement and other lower school activities (50% saturated)
If we don't use that strength, say because we don't know what strength we've made we cannot be said to have followed their advice should anything go wrong during a lesson

Cue the HSE investigation and the a**e kicking
 
Yes we do

CLEAPSS give a strength which is appropriate for use in halogen displacement and other lower school activities (50% saturated)
If we don't use that strength, say because we don't know what strength we've made we cannot be said to have followed their advice should anything go wrong during a lesson

Cue the HSE investigation and the a**e kicking
The recipes from CLEAPSS don't tell you how to get a known concentration though, so I don't see how they can expect you to know what you're giving out
 

CovTech

Lvl 38 Alchemist
COMMITTEE
The recipes from CLEAPSS don't tell you how to get a known concentration though, so I don't see how they can expect you to know what you're giving out
Yes it does
Recipe book says it's 0.6% w/v - as it also says that 0.6g in 100ml is the solubility therefore anything we make as per the recipe book is a saturated solution

So we make what the recipe book says - any of the 3 methods would be the same saturated solution then do a 50:50 dilution in water before it's handed out as per the Hazcard recommended strength
 
Yes it does
Recipe book says it's 0.6% w/v - as it also says that 0.6g in 100ml is the solubility therefore anything we make as per the recipe book is a saturated solution

So we make what the recipe book says - any of the 3 methods would be the same saturated solution then do a 50:50 dilution in water before it's handed out as per the Hazcard recommended strength
When I first read the CLEAPSS recipe I found it a bit confusing at first. Only because I glanced over the sentence about it making 0.6% w/v chlorine water at the top of the page... Might just be because of the caffeine hitting before making it :laughing:
 
Yes it does
Recipe book says it's 0.6% w/v - as it also says that 0.6g in 100ml is the solubility therefore anything we make as per the recipe book is a saturated solution

So we make what the recipe book says - any of the 3 methods would be the same saturated solution then do a 50:50 dilution in water before it's handed out as per the Hazcard recommended strength
It says a saturated solution is 0.6%, it doesn't say the methods make a saturated solution.

'bubble chlorine gas into water until the solution turns light green' and 'dilute to a suitable volume with water' are both completely subjective

It also says at the top of the page 'It is difficult to make up solutions of known concentration, trial prepared solutions before use to check that they produce the desired result'
 
Last edited:
I honestly just bubble chlorine gas through water for about 5 minutes-ish. Works fine. You don't need to get hung up on exact concentrations unless you're doing quantitative work. If it gives a good enough colour change it's fine...

I also just use smell to see if it's strong enough. Don't tell CLEAPSS.
 
Yes it does
Recipe book says it's 0.6% w/v - as it also says that 0.6g in 100ml is the solubility therefore anything we make as per the recipe book is a saturated solution

So we make what the recipe book says - any of the 3 methods would be the same saturated solution then do a 50:50 dilution in water before it's handed out as per the Hazcard recommended strength
a working conc of 0.3% w/v then?...I just have vague suggestions on mix stuff up and add some water :p
 

CovTech

Lvl 38 Alchemist
COMMITTEE
It says a saturated solution is 0.6%, it doesn't say the methods make a saturated solution.

'bubble chlorine gas into water until the solution turns light green' and 'dilute to a suitable volume with water' are both completely subjective

It also says at the top of the page 'It is difficult to make up solutions of known concentration, trial prepared solutions before use to check that they produce the desired result'
Fair enough then, that's not how I interpret that
If we're not making saturated solutions all that information in italics is entirely extraneous

Plus what's left in the beaker matches the physical description of a saturated solution from the Hazcard
 
If we're not making saturated solutions all that information in italics is entirely extraneous
Figured I'd do a morning coffee-ridden calculation; If you follow the sodium chlorate (I) recipe (which is how I my chlorine water), you take 10ml 10-14% w/v available chlorine and add 80ml water + 10ml HCl. Ignoring the HCl for a sec you'd get a 11-fold dilution which means 0.91 - 1.28% w/v available chlorine in solution, above the 0.6% w/v on the recipe.

NaOCl + 2HCl -> NaCl + H₂O + Cl₂ means that you put in 0.01 moles HCl (1M * 0.010L), therefore 0.05 moles of Cl₂ made for a complete reaction.
0.05 moles / 0.1 L = 0.5M of Cl₂. This is well above the saturated 0.085M solution...

From how I see it (given I've done it right); it has to make a saturated solution no?

Edit: I'm stupid is 10-fold, it mean's you get 1 - 1.4% w/v available chlorine, point still stands.
 
Figured I'd do a morning coffee-ridden calculation; If you follow the sodium chlorate (I) recipe (which is how I my chlorine water), you take 10ml 10-14% w/v available chlorine and add 80ml water + 10ml HCl. Ignoring the HCl for a sec you'd get a 11-fold dilution which means 0.91 - 1.28% w/v available chlorine in solution, above the 0.6% w/v on the recipe.

NaOCl + 2HCl -> NaCl + H₂O + Cl₂ means that you put in 0.01 moles HCl (1M * 0.010L), therefore 0.05 moles of Cl₂ made for a complete reaction.
0.05 moles / 0.1 L = 0.5M of Cl₂. This is well above the saturated 0.085M solution...

From how I see it (given I've done it right); it has to make a saturated solution no?

Edit: I'm stupid is 10-fold, it mean's you get 1 - 1.4% w/v available chlorine, point still stands.
so you're making excess then randomly diluting to a "suitable volume"....:heart: science :p
 
so you're making excess then randomly diluting to a "suitable volume"....:heart: science :p
I mean sorta :laughing: In reality there's a few issues with the calculation that isn't addressed. First is bleach doesn't keep it's 1% chlorine availability for long so probably overdoing it means you get more consistent solutions. Also any excess chlorine just fumes away once it's made so. Essentially you'd end up getting that 0.6% solution or close to it so I just assume a 0.6% and dilute from there.

I think the wording CLEAPSS uses is to make technicians think more about is the solution suitable or not and avoiding giving direct information due to the inconsistency of the process itself.
 
Top