Australia's Science Forum

Wondering if anyone has an online .... screened methyl orange colour chart?
I have just made a fresh batch for titrations, and its turning all the colurs under the sun, EXCEPT the grey end point that I wa s looking for. What colour is the end point supposed to be?
Link please??!!

Am I on the wrong track here?
Page 132 of "The Laboratory" says that Methyl Orange is red at pH 2.8 and yellow at pH 4.6
Is that what you are after?

Ian

Hi All,

Dissolve 1g. of methyl orange and 1.4g. of xylene cyanol FF in 200ml. water and make up to 500 ml. vol. with ethanol. The purpose of a screened or mixed indicator is to produce a more pronounced colour change at the end point. These types of indicators consist of either a mixture of two indicators or a mixture of an indicator and an inert dye. It changes colour at pH 3.8 -- 4.1 from Violet/Grey to Green.

Keep in mind that there will be very little or no colour charts relating to Screened Methyl Orange due to the fact (As I describeed above) that Methyl Orange is Doped with an Inert dye which just makes the endpoint more prominent.

I have prepared in the past in Industry the very same solution with perfect results every time.

Just have a look at the pH of your Screeded Methyl Orange and let me know what it is. Maybe the solution begins at the wrong pH unit.

((Ian).... I have left a Private Message for you...)

Hope this has cleared some frustration....

Cheers,

Robb.....

Robb

I arrived this morning, accessed the Chemtalk for help & info.Thanks guys
OK...so I set up some OH and H to test the colours. Tested the pH of the indicator 6.8
Preparing to do battle! Since the indicator was acting more like Universal indicator... with no discernable "end point" (ie no grey!)
I thought that the pH may not make so much of a difference... 6.8 not too bad, and only a few drops are going into the titration anyway.

Anyhoo.....There has been an amazing transformation in the 24 hrs since I made it up!
Yesterday it was changing from indigo-> dark blue->aqua->green->purple->orange->red!Every colour EXCEPT grey!
Phew!
So here am I gearing up to retest this again this morning, to find its working beautifully.
red->grey->green. Then green->grey->red. And with a tight little end point...(sweet)
The only thing that I can think of is that it needed to "rest" for 24 hrs?
Anyone heard of that before?
.PS Robb..... I didn't recieve a private message from you

Hi All,

Rainbow Sky, I can safely say that the 24 hour settling period may have come from the Xylene Cylanol FF solution. This could be from an old solution. As the Xylene Cylanol FF is susceptible to CO₂ from the atmosphere (very sensitive) it looks like it has taken some time to adjust to its correct pH hence colour, consider this also, the time delay is also helped as there is a slight Buffering effect within the solution..

I hope this has cleared things up for you, and to add a little confidence to your prep..


Cheers,

Robb.....

Thanks Robb
I will remember that next time

Barb,
I have a recipe for screened methyl orange that we use regularly.

Methyl orange - 1.0g
Indigo carmine - 2.5g

Dissolve powders in 1L distilled water. Filter before use.
pH range 2.9 (purple) - 4.6 (dark green).
The colour change is much clearer than normal methyl orange, though the shelf life is shorter.

Hope this is of some use
Judy

Just thought that I'd let youz all know... my screened methyl orange lasted for 24 hrs at "normal", before reverting back to the "rainbow" form. Frustrating. I heaved the lot, and am going back to my good old tried and true , plain old Methyl Orange! Pointless doing a titration if no-one has a clue re the end point!
Thanks Judy for that recipe. I will give that one a spin!

Dear All - Just discovered "Screened" Methyl Orange indicator!!!! I have always battled trying to decide the "end Point" when using regular Methyl Orange for acid/base titrations - can never decide exactly when the orange goes to yellow or vice versa, very "iffy", always been a bit of a lottery. However was reading an old Science book which mentioned the screened methy orange indicator and I found a recipe in the "the Labatory" (The one with the Xylene Cyanol - the colours go from purple to green with the end point a muddy greyish colour) mixed it up and did a test run and I found it much easier to see the colour change from the geen to grey and purple to grey. So I'm very happy about that and thought I would share this with everyone, or am I telling you something you know already and I've just been a little slow!! Judy

Please help! Our chem students are doing titrations using screened methyl orange.. but the colours are mutating as we speak!

I am wondering if regular Methyl Orange has the same pH end point as the Screened Methyl Orange?

Just googled it and found this
http://www.chemistry-react.org/go/Faq/Faq_3745.html
Hope it helps!!

Hi Rainbow-Sky,
I am not an expert, but have just read a paragraph from Nuffield Chem website

http://www.chemistry-react.org/go/Faq/Faq_3745.html

It would suggest that the Screened Methyl Orange is just ordinary Methyl Orange with a dye added to make the colour changes easier to see between yellow and orange. That would suggest to me that the end points and range would be the same, only the colour is different. Why not give it a go and see if you get better results. We call it "Learning through experiment".

Just read the Wikipeadia article. It suggests that MO ranges between 3.1 (red) and 4.4 (yellow), where SMO ranges between 3.2 (purple) and 4.2 (green)

Cheers
Ian

Not much difference really between the two then Ian.

Whoever said that screened methyl orange is easier to use than the regualr MO, are telling porkie pies! (just my opinion!)

Thanks Rae.. yes, it all helped

Hi All,

I hae completely forgot to tell you... So sorry. My private message to rainbowsky should have been that the end point for Screened Methyl Orange is Steel grey... (Faint Steel grey).

This is the correct endpoint for the solution. It is a considerable change to what Methyl orange has. But for the required endpoint screened methyl orange can only achieve this.

Also just FYI, Screened indicators are great to bring out better contrasting colours but you need to know what you are doing.

Cheers,

Robb.....

Hi
I think the methyl orange end point is hard to see so a mixed indicator is worth a try. Who supplies Xylene Cylanol?I cant find it in Q stores or Serrata catalogues.
Debbie

Hi All,

This is a specialty chemical and will need to be specifically ordered in from a ruputable chemical supplier.

Expensive too...

Cheers,

Robb.....