Sodium hypochlorite 15%

Good afternoon chemists,

In our school, a year 12 student needs to use sodium hypochlorite (NaClO) to do an experiment of his.

The purpose of this experiment is to determine to what extent NaClO exposure damages a cotton thread. To do this, we will prepare five dilutions starting from a concentration of 15% (13%, 11%, 9%, 7% and 5%) and leave a cotton thread in each of them for a determined amount of time. Afterwards, we will test the strength of the cotton thread he left in each of the six NaClO solutions.

Since NaClO at 15% concentration is toxic, we plan to prepare the solutions for the experiment in a fume cupboard, in a well-ventilated room. Obviously, we will be wearing a lab coat and gloves. We also plan to wear a face mask to reduce exposure to NaClO. We will use the smallest possible volume of NaClO. Me, the technician, will prepare all but the weakest (5%) solution (that one will be made by the student). Of course, he won't be left alone under any circumstances.

My questions are: are we doing this right? Is it safe for a Y12 student to prepare a 5% NaClO solution? Do you have any suggestions as to how can we protect ourselves better from NaClO?

Thank you.
 
if this is for a yr 12 practical investigation (coursework) then I think the student should be making the dilutions.
 
It is however x3 times the strength of domestic thick bleach but yeah still not that scary. My clothes will attest to the damage done to cotton when not donning lab coat.
 
Hi,

Thank you all for your answers.

I just learned that our student is asthmatic... is that an issue if he prepares the NaClO dilutions in the fume cupboard? (I have just asked CLEAPSS but they haven't answered yet, and we need to know this for tomorrow...).
 
Agreed, sodium hypochlorite really isn't that scary. You'd let a 16 year old clean the toilet, NaClO is just bleach.
Agreed... they use it to clean swimming pools, and I don't think the staff there uses a fume cupboard nor any special equipment (aside from gloves) when manipulating it.
 

CovTech

Lvl 38 Alchemist
COMMITTEE
Hi,

Thank you all for your answers.

I just learned that our student is asthmatic... is that an issue if he prepares the NaClO dilutions in the fume cupboard? (I have just asked CLEAPSS but they haven't answered yet, and we need to know this for tomorrow...).
If it's an urgent request you can ring them to find out don't forget

I'd still be iffy about giving it out without CLEAPSS go ahead as the Hazcard just says for 5% and over but 15% is too far beyond of that for me to assume it's covered by the same permissions
 
If it's an urgent request you can ring them to find out don't forget

I'd still be iffy about giving it out without CLEAPSS go ahead as the Hazcard just says for 5% and over but 15% is too far beyond of that for me to assume it's covered by the same permissions
I asked them if it was fine to work with NaClO at 15% in a fume cupboard, using gloves, etc., and they said it was fine, but also asked if the student is asthmatic. I answered today he is... I guess this complicates everything.
 

CovTech

Lvl 38 Alchemist
COMMITTEE
I asked them if it was fine to work with NaClO at 15% in a fume cupboard, using gloves, etc., and they said it was fine, but also asked if the student is asthmatic. I answered today he is... I guess this complicates everything.
Yeah I'd ring them if you've not heard by 2pm today cos you won't hear back until Tuesday if you don't
 
I have called CLEAPSS them, and they told me he should be fine if he does everything inside the fume cupboard. Since we haven't tried this out before, I am not sure it's going to work...

Any feedback is welcomed.
 

CovTech

Lvl 38 Alchemist
COMMITTEE
In terms of the practical I have no idea with trialling

Does the Bleach affect the thread with enough difference at that spread of concentrations to be noticeable or does it need a broader range?
How's the student planning on testing the tensile strength of the thread after it's treated?
I'm not even sure if cotton is damaged by bleaching - isn't that how they make it white instead of the off-yellow it naturally is?
 
In terms of the practical I have no idea with trialling

Does the Bleach affect the thread with enough difference at that spread of concentrations to be noticeable or does it need a broader range?
How's the student planning on testing the tensile strength of the thread after it's treated?
I'm not even sure if cotton is damaged by bleaching - isn't that how they make it white instead of the off-yellow it naturally is?
If it's an KS5 investigation as part of the course then it's the students and the supervising teachers problem.
 
In terms of the practical I have no idea with trialling

Does the Bleach affect the thread with enough difference at that spread of concentrations to be noticeable or does it need a broader range?
How's the student planning on testing the tensile strength of the thread after it's treated?
I'm not even sure if cotton is damaged by bleaching - isn't that how they make it white instead of the off-yellow it naturally is?
I think he's going to use mass hangers and a weight of 15 lbs to test each cotton thread.

Yes, I have also read that bleach just whitens fabrics rather than damaging them.

The NaClO hasn't arrived yet, so maybe he won't be able to do his experiment tomorrow :(. We would have tried this out before Saturday had we had the NaClO or bleach.
 

clairelucas

COMMITTEE
Good for you
Some of us have trialling the experiments as part of our duties
Trialling class practicals I'm fine with, but this is a student proposing a method. Apart from making sure its safe for him to do, trialling and assessing possible errors is his job...
 

CovTech

Lvl 38 Alchemist
COMMITTEE
I'm not trialing 30+ individual student investigations, i'll advise them only.
I do it because it's in my job description
I don't mind it being there because teaching staff have literally zero time to do it and even if they did they have barely any ability to do it decently
What's the point of sending out a practical you know isn't going to work because you're making some point about making them do something they won't do properly anyway - that's a waste of our time setting it up and the students time doing it

Once it's planned out and a working practical I make them come and try it before teaching but I don't have the space in the preproom for a constant revolving door of people "planning" experiments

Trialling class practicals I'm fine with, but this is a student proposing a method. Apart from making sure its safe for him to do, trialling and assessing possible errors is his job...
What they plan and what they do in the lesson don't need to be the same thing ;)
With the "students plan their own experiment" we often let them get on with the planning and risk assessment and then the teachers marks what they planned but makes them do our version so they have one that works and is safe and they can get results/not kill themselves/not blow up half the building :laughing:
 
In terms of the practical I have no idea with trialling

Does the Bleach affect the thread with enough difference at that spread of concentrations to be noticeable or does it need a broader range?
How's the student planning on testing the tensile strength of the thread after it's treated?
I'm not even sure if cotton is damaged by bleaching - isn't that how they make it white instead of the off-yellow it naturally is?
Trust me bleach can easily damage cotton, based on recent experience & in my youth when dyeing clothes…had a pair of jeans basically disintegrate when left in domestic bleach for far too long.
 
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