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Topic: How to delay change of color of a reaction?  (Read 2102 times)

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Offline Illusionist

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How to delay change of color of a reaction?
« on: September 25, 2022, 03:56:28 PM »
Hello, i am not a chemist, so sorry for the noob question.

If i mix Iron(III) chloride and potassium thiocyanate, the reaction should produce immediately a red liquid, correct?

How can i do to retard the change of color (for example after 60 seconds of mixing them)?
« Last Edit: September 25, 2022, 04:59:37 PM by Illusionist »

Offline Borek

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Re: How to delay change of color of a reaction?
« Reply #1 on: September 25, 2022, 07:06:58 PM »
You were already told there are no simple tricks that can do that, if you hope to get a different answer you are out of luck. Chemistry won't change just because you will ask again.
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Offline Illusionist

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Re: How to delay change of color of a reaction?
« Reply #2 on: September 26, 2022, 09:33:50 AM »
My question is different from the other (the ingredients are completely different), and by the way, some kind of clock reactions CAN be delayed (the coloration), by simply adding distilled water.

This is why it's called "Clock reaction". Am i correct?

I am asking if, with this reaction too, is possible to do the same, in some way.

Have a nice day

Offline Borek

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Re: How to delay change of color of a reaction?
« Reply #3 on: September 26, 2022, 03:35:55 PM »
My question is different from the other (the ingredients are completely different), and by the way, some kind of clock reactions CAN be delayed (the coloration), by simply adding distilled water.

It is not that simple. If you add water in some cases you can slow the reaction, but you will also end with a weaker color. Or no color at all. There is plenty of fine prints here.

Quote
This is why it's called "Clock reaction". Am i correct?

Nobody uses these reactions to measure time, this is a rather lousy and catchy name that doesn't mean much.

Quote
I am asking if, with this reaction too, is possible to do the same, in some way.

No.

Technically there is nothing that makes process that will produce effect you need impossible, but I am not aware of any reasonably simple reaction that can be done with reasonably cheap and available reagents. Apparently others don't know such reactions too.
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Offline Illusionist

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Re: How to delay change of color of a reaction?
« Reply #4 on: September 27, 2022, 08:39:13 AM »
Thanks for the reply.

Offline Enthalpy

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Re: How to delay change of color of a reaction?
« Reply #5 on: October 10, 2022, 06:15:13 PM »
If this shall serve a scene effect, I feel easier to have a lamp that gives the colour change, and switch it on after a delay, possibly with a slow intensity increase. The lamp itself could have the right colour, or it could be ultraviolet and the liquid be fluorescent.

Alternately, invisible light could produce a reaction that changes a colour.

Only from mixing chemicals, the effect won't be perfect. For instance the dissolution of a powder takes time, as is known from sugar in coffee. For instance phenolphthalein would be colourless in an acidic solution, you could add and mix a basic powder, and as the powder dissolves it makes the solution basic and the phenolphthalein pink. An effervescent powder would dissolve without much mixing. But the solution will turn pink at some places sooner, for instance at the bottom if the powder sinks. A fine powder can sink ("sediment") very slowly in a viscous liquid, hence stay uniformly dispersed. The initial acidity tunes the delay. Other combinations of compounds may give nicer colours: potassium ferro/ferricyanide, etc.

A clearer onset: use chemical that change colour quickly but in a geometrical arrangement that delays their mixing. Have the colour-producing compound at the bottom of a pot, topped by some compound that disappears slowly in the solution. Or the colour-producing compound could take time to percolate through a powder.

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