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Chemistry / Can the colour change of litmus indicator be explained by conjugation?

« on: 30/10/2016 21:44:20 »

I have been trying to understand the colour change in litmus paper from a quantiative point of view. I have knowledge of the particle in a box model of quantum mechanics, and i would like to apply this to the conjugated system in the active indicator-component of litmus dye.
In other indicators I have looked at, you can clearly see that when the dye molecule dissociates or is protonated, there is change to the length of the conjugated system (number of alternating double bonds in a row), which explains the colour change. An example is given below for BTB (bromo thymol blue)
[Image 1]

However, i can't find any explanation like this as to why the indicator dye in litmus paper (7-hydroxyphenoxazone) changes colour when protonated/deprotonated. From what I can see, the length of the conjugated system is the same in both versions of the molecule.
[Image 2]


  [Image 1]: https://i.stack.imgur.com/Wtsb7.png
  [Image 22]: https://i.stack.imgur.com/gpZ8t.png

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Chemistry / Why is the colour of the aurora determined by Oxygen, rather than Nitrogen?

« on: 12/10/2016 11:32:18 »

Recently I moved to the north of Norway, so I've seen quite a few auroras. Because the colour is mainly green, I was sure this must be due to electron transitions in N2 (because the atmosphere is like 75% N2)
Looking into this, however, I found out that the colours of the aurora are mainly due to electron transitions in atomic oxygen gas. Why is it that the electron transitions of oxygen are most prevalent in the colours of the aurora, even though it is far less abundant than nitrogen?

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Chemistry / Re: How do indicators work in chemistry?

« on: 07/08/2016 22:00:22 »

Given the structural formula of the active substance in red cabbage indicator. Is it possible to determine what colours it will absorb and reemit from first principles? I am guessing if it did it would involve alot of quantum mechanics, but surely it is possible to use the shrodinger equation to figure out all the allowed electron energy states ?

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Chemistry / Can you make a galvanic cell work with no salt bridge?

« on: 01/04/2016 22:53:59 »

Hello.

This week i was playing around with a galvanic cell at school. I made several attempts to make it work without the salt bridge. It was a cell with a copper electrode  and a zink electrode. All my attempts failed.

The thought came to mind that i might be able to make it work if i somehow made the solution surrounding the zink rod concentrated with negative ions, and the solution surrounding the copper rod concentrated with positive ions.

The obvious problem with the idea is getting the solutions with heavily scewed charges. I can't think of any way to achieve this. Is there a way?

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Chemistry / Does fehling's solution oxidize alcohols? Why not?

« on: 23/02/2016 12:38:52 »

If not, how come it can oxidize aldehydes to carboxylic acids and not alcohols to aldehydes/ketones?

Does fehling's solution have any other use besides oxidizing and testing for aldehydes/reducing karbohydrates?

All input is appreciated

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General Science / Re: How should i remove stink from compost bin?

« on: 08/02/2016 12:33:36 »

Thanks for the input guys, i will try it out when i have time. I will make sure to let you know how it went when i eventually do it

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General Science / How should i remove stink from compost bin?

« on: 06/02/2016 17:31:27 »

Hello

I have been using a plastic beach cooler to store food scraps in my kitchen prior to composting. After much use it has started to smell even when empty. I have tried cleansing it with regular kitchen soap, but it has had little to no effect.

Does anyone have any smart ideas that might remove the smell? A Chemical explaination of the suggestion would also be appreciated, as i am a chemistry student.

All input is appreciated!

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Physics, Astronomy & Cosmology / Re: What is the solution to a particle sliding down a hemispherical surface?

« on: 01/02/2016 11:17:28 »

I have figured it out. Thanks for all the input.

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Physics, Astronomy & Cosmology / Re: What is the solution to a particle sliding down a hemispherical surface?

« on: 30/01/2016 23:19:28 »

I don't understnad. v_x is close to zero to start With, and then it accelerates as the particle moves Down the hemisphere due to the reaction force from the surface. I dont understand what this "initial velocity" you are talking about is.

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Physics, Astronomy & Cosmology / Re: What is the solution to a particle sliding down a hemispherical surface?

« on: 30/01/2016 22:11:26 »

I still do not understand. If you see exactly what i am missing, can you please explain in a more comprehensive way? Instead of just 1 liners which don't give me much understanding.

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Physics, Astronomy & Cosmology / Re: What is the solution to a particle sliding down a hemispherical surface?

« on: 30/01/2016 15:19:55 »

It already defines the initial velocity as v_x.

But the problem arises when they og further With the Equation. Because to form Equation 2 they use that the total horisontal velocity of the particle is v_x+V_x. This implies that the v_x is not allready the sum of the different horisontal Components.
See the Attached picture

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Physics, Astronomy & Cosmology / Re: What is the solution to a particle sliding down a hemispherical surface?

« on: 30/01/2016 10:03:35 »

Yes, isn't the horisontal momentum of the particle relative to rest equal to m (v_x-V_x)?

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Physics, Astronomy & Cosmology / What is the solution to a particle sliding down a hemispherical surface?

« on: 29/01/2016 20:45:17 »

The problem is displayed in the picture which is attached, as well as the start of the solution. I follow the solutions reasoning except for the very first equation which the rest is based on.

Why do they solve conservation of momentum as mv_x=MV_x instead of m(v_x-V_x)=MV_x?

My thought process is that the particles net velocity is the velocity of the particle horisontally Down the hemisphere, minus the hemispheres velocity to the left. Therefore the momentum of the particle is the velocity sum times the mass: m*(v_x-V_x).

I've been looking for this for over two hours. If anyone can spot the mistake in my reasoning it would be greatly appreciated.

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Chemistry / Re: Why does a rough surface encourage water to form droplets?

« on: 25/01/2016 21:47:28 »

Within a given boundary, a rough surface will have a greater area of exposed material than a smooth surface.

Hydrophilic and hydrophobic behaviors are surface interactions.

More area = more interaction.

I dont see how that explains the lotus effect, where the droplets barely touch the surface. They kind of float along on the air bubbles inbetween the microstructures.

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Chemistry / Re: Why does a rough surface encourage water to form droplets?

« on: 25/01/2016 16:09:02 »

The following may be involved:  The more synclastically curved a surface is, the lesser area of it is required to accumulate a given force per unit length of periphery because the lay of the surface deviates from flatness over a shorter distance. Therefore, if a sphere of liquid encounters a hydrophobic surface that is flat, that deforms the surface the same as does placing a basketball on the floor, resulting in tighter curvature in certain areas that repels it from the floor enough to stabilize it there. However, if you take the same basketball and place it on a surface having irregularities that are substantial but smaller than the diameter of the ball, and try to force the ball into the same amount of contact that it had with the flat surface, it will resist more vigorously because the curvature required to make it  conform to the surface is greater.  That suggests that hydrophobic liquids will tend to have less contact with a rough surface than a smooth one at any given pressure, because the surface tension resists deforming so as to match the roughness.

As for hydrophilic surfaces: Because they tend to attract the liquid, the liquid will tend to cover the surface. It is energetically favorable for the liquid to contact the entire surface rather than just the high points of it, which it will try to do. But there is also the issue of the surface tension on the exposed side of the liquid. The liquid will try to keep that surface flat.   The volume of the available region is determined by the thickness of the region of roughness. If the amount of liquid is less than this volume, it will not be able to assume a fully flat surface on the outside, and will develop a negative pressure (relative to the environment) because of the conflict, and if additional liquid  becomes available, it will be pulled into the system as the system tries to flatten its outside surface. Thus, the rough surface will tend to adsorb liquid until its roughness is filled.  On a flat (smooth) hydrophilic surface, of course there is no roughness and therefore no roughness volume, so there is no energy advantage for a thin layer of liquid more than several molecules thick to become thicker.

I like the basketball analogy, thinking of the basketball shell as the surface tension holding in the liquid. Quite intuitive

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Chemistry / Why does a rough surface encourage water to form droplets?

« on: 24/01/2016 22:21:24 »

Lately I have been reading about this topic and one of the things I found out is that if you have a rough, textured, surface, this will make a hydrophobic interaction more hydrophobic and a hydrophilic interaction more hydrophilic.

I have found many equations describing different types of wetting, but they seem to be relating the contact angle, roughness and amount of surface contact. What I dont understand is WHY does making a surface rough make it water form into a sphere (in the case of a hydrophobic coating) but make it spread out more (in the case of a hydrophilic coating)?. How is it different from simply a flat polar or non-polar surface?

Im sure I have read an explaination but totally missed it because I dont understand a lot of the terminology used. Can someone explain in a way I understand?

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Chemistry / Re: Stereoisomers - Unsaturated compound with chiral centre

« on: 21/01/2016 21:09:33 »

That is correct.        R1      R2          \      /The      C=C     structures can only lead to different isomers if R1 ≠ R3 AND R2 ≠ R4.          /      \        R3      R4Additionally, if R1 and R2 (or R3 and R4) are connected in a ring that contains fewer than 8 consecutive bonds, there is only one  stereoisomer that is physically possible (R1 and R4 cannot be connected in a small ring).

Thank for you for broadening my understanding. Is the number 8 a set limit, or is it just a rule of thumb? I guess the limit has to do with the stereochemistry of the different bonds, lenghts and angles ?

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Chemistry / Re: Stereoisomers - Unsaturated compound with chiral centre

« on: 17/01/2016 10:22:25 »

Ah, i understand it now.
Correct me if my understanding is wrong.

The bond i marked has a carbon with two methyl groups, so it can't occur as stereoisomers.
The double bonds in the cyclic structures can only occur in that one configuration for the loop to be complete.

Therefore the only two isomers of the compound come from the chiral centre.

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Chemistry / Why does this shikonin molecule have only 2 stereoisomers?

« on: 17/01/2016 01:34:03 »

Hello.
Can someone explain to me why this compound only has two stereoisomers? It follows Le Bel-van't Hoff rule, but I dont understand why the double bond marked on the picture doesn't give 2 more stereoisomers.

What about the double bonds in the cyclic structures?

I can't find any information online about stereoisomers in compounds with both double or tripple C-C bonds as well as chiral centra

Thanks in advance!  []
 [ Invalid Attachment ]

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Chemistry / Re: Saturation point understanding, salts in water

« on: 16/01/2015 17:47:24 »

The real issue is the equilibrium between ionic solid and solvated ions--the ions have opposite charges, so they are attracted to one another. We have to account for the attraction of the ions to each other versus their attraction to the water. If it were just about having enough water molecules to surround the ions, how could you explain the difference in solubility between NaCl and AgCl?

As you increase the concentration of ions in solution, you are also decreasing the average distance between the ions, thereby increasing the effect they have on one another.

Aha. Good explaination, really cleared up all my questions, I allready know about K_sp, it was just my understanding of what a Saturated solution actually meant that got me confused. Many thanks!