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Hi all

I have been working slowly through my new GHS labelling and have found a slight discrepancy with methyl orange indicator. In our Labbie Bible ie "the Laboratory" the recipe adds 1g methyl orange to 200ml ethanol and 800ml water. This has a colour range of pH2.8-4.6. However on Chemwatch all the SDS's for the indicator do not use ethanol and the colour range is pH3.1-4.4 and also has Nil hazard (except the screened version which is different).
My question is: should I make it up the way in the book and therefore will need some kind of hazard grading or should I just use water?
Does anyone have any idea??

Thanks in advance
Kathryn

I've only ever used distilled water - pH 2.8 to 4.6

sorry to add to the confusion, but I follow the book.

I've found that as well. I have found that there is a supplier MSDS /label that has it made up in 20% ethanol, so that is what I have used . I have a few litres of the stuff in stock and dropper bottles, so I don't really want to throw it all out. I would also like to hear other's ideas.

Only ever used the distilled water.

I have used 20% alcohol pH about 3-4.5.
Don't throw it out, Curie

Hmmm interesting. My old "Handbook of Laboratory Solutions" is 200ml ethanol up to 1 litre as well, but the Methyl Orange/Bromocresol green ind is just water? so I don't get it. Maybe the alcohol dissolves it better or alternatively preserves it longer??? I make mine up with ethanol and water through habit though.

My labels for methyl orange indicator carry the flammable warning. I have always used ethanol in preparing this indicator.

Jumping into a very old thread here... But I have a request for methyl orange indicator for a titration. It's CaCo3 and HCl. Should I be recommending a different indicator? This one only does from pH 3.2-4.4 according to google, but the bottle (screened methyl orange) says Alkaline green, acid magenta with transition grey at pH 3.8. I don't see how that's going to give an accurate result! I've always used phenolphthalein in the past from memory. The teacher is just going by what the textbook says.

My initial understanding of the titration prac is for the students to titrate a base into an acid until a basic/neutral solution is reached. If this is the case for your situation, i'd agree that their results wont be very accurate as Methyl Orange's 'transition colour' occurs at pH 3.0-to-pH 4.8 and 'neutral' pH is reached at a reading of pH 7. However, if they arent necessarily trying to get a basic/neutral solution, rather just practicing their titration technique by ensuring a solution reads a certain pH, I dont see there being a problem. The teachers here have always asked for multiple types of indicators (i.e. phenolphthalein, methyl orange, bromothymol blue, etc) when doing this prac.
Furthermore, i could be wrong so please dont take my word for gospel xD

They are trying to calculate the concentration of acid.

Im of no help but for Titration we have always used Phenolphthalein.