Harry_-

Sorry I don't have lots of time to write a reply at the moment I'm working on a lab. However if you can find the redox potentials for the cell you could use:

ΔG^o= nFE

n is the number of moles used in the balanced equation

F is faraday's constant of 96500 Cmol^-1

E is your cell potential under standard conditions (reduction - oxidation potentials)

If you need help ask or there are lots of good online videos on that equation.

Regards,

Harry

Thanks so much. I'm preparing a lab experiment and can't really reference that, are there any papers that I could use?

Also I notice that the yield for that experiment is 72% whereas without ammonium nitrate and with a lot more cupric acetate monohydrate the yields on the other paper are 90%. Why is this?

They say nitric acid can be used but nothing about ammonium nitrate

What about the ammonium Nitrate. I can't find any papers on it being used in this reaction

Does anyone know how this reaction proceeds with the following reactants?

Glacial acetic acid (i presume solvent)

Cupric acetate monohydrate 

Ammonium Nitrate

Hello,

I'm researching into the 2019 Nobel Prize for chemistry, and therefore lithium ion batteries. 

Wittingham's battery was a lithium anode, a titanium disulfide cathode and a lithium perchlorate in dioxolane electrolyte.

I have always thought that batteries rely on a displacement reaction split into two halves. However in animations that I have seen show the electrons at the cathode being picked up by the very lithium ions that released them and that have just moved from the anode to the cathode. This doesn't make sense to me as if the lithium is picking up the electrons it just gave away what was the cause for this reaction to take place? I would have expected the electrons to be picked up by the electrolyte. What is happening here? 

Any help would be greatly appreciated,

Harry

3 minutes ago, studiot said:

A thought about solutions occurs to me.

Did you take water of crystallisation into account in your weighing out of the chemicals?

http://www.docbrown.info/page01/AqueousChem/AqueousChem5.htm

They give 5 for copper sulphate and 7 for magnesium, which is the same as zinc.

Yes, I did take these into account, I can't remember what the exact values were for each compound but I used the value on the bottle. However if the bottles were contaminated/ not pure (very possible as I was using school chemicals which students in practicals can just scoop out what they need directly from the bottle using a spatula) wouldn't this cause my entire gradient to be off as in dilution I wouldn't be making the concentrations of the solutions I thought I was making. 

I also was only using a 2 d.p scale (only one I have) so I cannot expect each solution to be the exact same concentration.

5 minutes ago, studiot said:

V = IR

Since V was of the order of 1 volt, what value of current does that make I ?

I don't see any good reason why the equal concentration voltage was not 1.1 volts either.

But hey, never mind, you have learned a lot and had some fun.

This is also weird to me as if the electrometer was in parallel, I would expect a slightly lower value for standard emf (due to the lost volts not completely being cancelled out by the resistor) however if the electrometer was in series I would have expected a very precise value of E⁰.

What if the ZnSO₄ or my CuSO₄ wasn't perfectly pure therefore each of my subsequent solutions were slightly off so even my standard emf (if [reducing agent] was larger than [oxidising agent]) would be lower than expected. As I added water to my solutions to make them more dilute this could have changed the shape of my graph.

I'm also having a hard time believing I would put a voltmeter in series 😂

23 hours ago, studiot said:

Just spotted this, which may be the problem.

 

I don't know what your resistor(s) were in series with the electrometer but I think the input resistance to the meter might have been to high.

5x10¹³ Ohms is huge.

Can you repeat with something like 10 to 100 MΏ in parallel with the meter?

I assume you had selected voltmeter mode?

Unfortunately I do not have the equipment anymore. My circuit drawing is setup for measuring current and not voltage, It has been a while since I did this experiment so I'm not sure if I put the electrometer in series with the resistors or if I set it up the correct way. Its embarrassing I know. However, even if my electrometer was in series with the resistor (100M Ohm) the voltmeter's impedance is 5x10¹³. Compared with 100x10⁶ of my resistor in series, shouldn't this mean that my results should still be accurate to the degree that I have.

8 minutes ago, studiot said:

Thanks for the data so far, what were the concentrations you used?

I have been working through your figures.
No you have not made an arithmetical error.

But the slope of your graph is 0.026 and it should be 0.012

I haven't figured out why yet, but I'm working on it.
 

Meanwhile here is some data from someone (Petrucci - General Chemistry) who has done your experiment.

Note that he changes from naperian logs to base 10 logs and also has a much wide range of concentrations.
Also example 19.5 in the middle of the page is nothing to do with the rest of the page.

My concentrations that I wanted to use started at molarity 2 and were tested against the other electrolyte of molarity 1.5 and 1.

I had an issue with creating 2 molarity solutions and the solutions were saturated, so I doubled the volume to make molarity 1 solutions as a start.

I could be possible that I made up the solutions wrongly as I was working very fast

18 minutes ago, studiot said:

Maybe this answer was too simple, I was just hoping since you are looking for a factor of 2.

 

I highlighted where is says the EMF of the complete cell is the algebraic sum of the two electrodes. But one is positive and one negative so the difference between them is twice their magnitude.

How did you connect your measuring apparatus ?

And what is measured along the bottom scale (x axis) on your graph - it is obscured on your attachment.

Standard Electrode potentials:

Zinc= -0.76

copper= 0.34

(both of these should account for the reaction using/ taking 2 moles of electrons)

0.34--0.74=1.1v

It is weird that I am pretty much exactly a factor of 2 off, which is why it makes me believe that iit is a calculation error rather than a practical one. For example, if I was only using 1 mole of electrons in the balanced ionic equation my value for F would be perfect.

Here is the electrometer I used's manual: http://physics-astronomy-manuals.wwu.edu/Keithley 614 Electrometer Manual.pdf

Here is a diagram of the apparatus setup, the electrometer being in series shouldn't be a problem should it? I assumed it had internal parallel circuits to record voltage as it also records current.

Finally, my x-axis was ln([Oxidising Agent] / [Reducing Agent])

1 hour ago, studiot said:

Since you have the factor of 2 (electrons transferred) in your calculations I wonder how you measured the voltage, ie what was your zero point since the cell voltage is double the calculated Nernst EMF, as described in the attachments.

I'm not sure what you mean by 'zero point' please could you expand. I used my electrometer to measure the voltage, it was zero-checked before the experiment and then connected to my circuit. What do you believe to be off in the recorded voltages? From my calculations the standard emf should be 1.1v, the value I got experimentally was 1.06 (mainly due to insufficient resistance in the circuit to negate internal lost volts).

Thanks  

@studiot

Hi,

I know it has been a while, so much has been going on. I have just been writing up my results from this experiment and have come across some trouble with my calculated value for Faraday's constant. It is almost perfecty half what it should be, one of two problems could have occured:

1) In my stupidity I created the wrong concentrations of solution (not very probable as all sorts of anomalous points would be created when I then made my more diluted/concentrated solutions)

2) Something is wrong in my calculations

Could any off you check these calculations to see if there are any problems. I used a Zinc anode and Copper cathode so my value for number of electrons transferred in the balanced ionic equation should be 2. If you require any more info, just say :).

Hope you are all well.

Harry

17 minutes ago, studiot said:

Here are a few states recognised by Chemists.

The crystalline state
The gaseous state
The metallic state
The amorphous state (charcoal, elastic, rubber etc)
The vitreous state (glass, supercooled boron trioxide)
The liquid state
The dissolved state
The disperse state (colloids)
The ionic state
The interfacial state
 

I'm glad you found phase diagrams because that was on my list of 12 little pieces ( not yet finished but here are some more)

(3) Binary mixtures , phase diagrams, eutectics, the phase rule.

(4) pH, pOH and p(X)

(5) Chemical applications of polarised light.

(6) The Boltzman distribution

(7) Metallic bonding and Fermi levels

(8) Electronegativity v electron affinity

Thanks so much for your continued help, I will look into all of these in the coming weeks. Your questions are also very helpful, I have upcoming interviews where they will be asking me questions similar to as you have just posed. I don't think my answer to Q2 was quite satisfactory and this is mainly as I don't think I understand the question, could you clarify the question further?

On 9/22/2019 at 5:37 PM, studiot said:

1) Chemistry recognises more states of matter than Physics, which recognises only 4 (solid, liquid gas ans plasma). Can you think of any?

Ok so this question took me longer than expected but I think I have an answer. I looked into the phase diagrams of water and found that at high pressures/ low temperatures , the liquid and gas state merge into something in between. I looked into it just a little and its called a super critical fluid, that's as far as I have got.

On 9/22/2019 at 5:37 PM, studiot said:

2) A large part of Physical Chemistry is about the combined action of large collections of particles which obey many common equations, for example the bulk of free electrons in a semiconductor have been called an 'electron gas' because they obey similar laws to the gas laws. So the 'particles' are not always molecules or even atoms.
Can you identify any more? Hint some are called colligative properties.

As for this question, I have just read 'A brief introduction to superconductivity' in which it explains that superconductivity is a quantum phenomena. I'll be honest, a lot of the quantum mechanics were too complicated for me however I learnt that in this superconducting state electrons work as pairs to flow through a superconductor. Is this an example of particles not acting as molecules/ atoms?

These are all good points. I have maths and physics A-level. Ok so random number won't work, has anyone got a topic which will be enjoyable? I have the 11th edition.

Hi,

I am a student in high school, wanting to study Chemistry at university. I am doing a challenge to read into a new chemical topic every week. I have here an Atkins Physical Chemistry textbook and would love it for whoever is reading to give me a random number between 10 and 850, this will be a page number and I will research that topic for that week. This forum will be an account of my progress and a place to get help on the topic.

Thanks

6 hours ago, studiot said:

Thanks for the vote.

One thing that confuses many people is the question of which is the anode and which the cathode, which is positive and which negative and which way does the current flow.

Understanding this leads to many exam questions.

Discussion of this this would be off topic here, so if you want more on that subject, start a new thread.

Thank you for your advice. I have two university interviews coming up for chemistry and your expertise is greatly appreciated. I will probably make a post looking for tips or interview questions which I could have a go at in my own time.

As for anode/cathode. I know that for a galvanic cell,  reduction happens at the cathode. Therefore electrons flow to the cathode and is consequently positively charged. In an electrolytic cell i believe it is the other way round.

I was wondering, why do batteries slowly run out over time? I presume in electronics such as a torch that the circuit is broken when unused so why does this occur?

Also I was wanting to let each student do this mini kids version. Here, yeast is the catalyst, does anyone know the exact decomposition reaction which is happening here? https://www.thoughtco.com/kid-friendly-elephant-toothpaste-demo-604164

1 hour ago, studiot said:

I've never heard of elephant's toothpaste, though I suppose they must have some arrangement.

Have you got a link?

 

% concentration could be w/w, v/v or w/v.

Since one phase is gas I would assume v/v.

Attached is my practical proposal. It has a link at the bottom that should explain things. Also here is a youtube link : 

Elephants Toothpaste Experiment.docx

1 hour ago, Strange said:

There are loads of articles on this online.They seem to suggest between around 50 and 100ml of hydrogen peroxide. (And recommend safety equipment.)

Ok so I have seen these but my plan is to scale it down so each student can have a mini experiment. Also I need to work out the volume I will create as if I make mess my teacher will kille me

Hi,

I am in secondary school studying chemistry. I chair the school's STEM society and am wanting to give a talk and practical on the elephants toothpaste that you may have seen online.

Elephants toothpaste is large amounts of oxygen trapped in soap. To make a plume of this, you use hydrogen peroxide  and a catalyst that releases the oxygen at an increased rate such as potassium Iodide (iodide ions are our catalyst).

I am wanting to give this demonstration to other students and need to work out the volume of 'bubbles' that will be made so that I do not make too much.

I will be using 100 volumes H2o2

Also I understand volume as a measurement of concentration in this case, however a lot of online sources use percentage. Do I take this as percentage by mass or by volume.

Thanks

5 hours ago, studiot said:

 

I am pleased that you will now be able to concentrate on the physical chemistry rather than the electronics.

So it is now appropriate to consider the challenges in what you are attempting.

Firstly the Nernst equation depends upon temperature.
The chemical action involved will change that.
This is separate from any electrical heating due to the curent drawn, which you will minimise by restricting the current using a high value resistor.
How will you measure the temperature and what accuracy will you require to obtain millivolt precision in your calculation?

Then there is the question of the value of the temperature.
Nernst assumes that the whole of the body of both solutions is at the same temperature and guaranteeing that, to one millivolt is no small order.

Then there is also the question of the accuracy of your concentrations.
Because of the difficulty in obtaining accuracy with small quantities when weighing out and transferring etc pharmacists, for instance, often make up far too much by a factor 10, 100 or even 1000 and dilute the solution by these factors.
This reduces the errors.
 

These are the chemical difficulties I can think of.

But there are also physical ones in measuring at or below the millivolt level.

One is contact potentials between connections and sections of the wiring.
Another is surface leakage when measuring at high resistance.
Another might be random radio pickup or noise from your 10% resistors.

The use of electrometers in physical chemistry is often accompanied by 'guard rings'.

https://www.google.co.uk/search?ei=bR16XaelEdSdgQbt26HABg&q=electrometer+guard+ring+measurements&oq=electrometer+guard+ring+measurements&gs_l=psy-ab.3...50948.56296..56690...0.2..0.132.906.8j2......0....1..gws-wiz.......0i71.Wx98sJBUdEM&ved=0ahUKEwjnj5OcicvkAhXUTsAKHe1tCGgQ4dUDCAs&uact=5

If you go on to do much electrochemistry these considerations will become commonplace for you (as will electrometers).

Go well and let us know how you get on.

 

 

I am also happy to get away from the electronics :)

As for temperature, my maximum resolution is 0.1 kelvin due to equipment av available. Obviously this isn't ideal with my level of precision of voltage but without that precision I wouldn't see any change in voltage and therefore would have no results to show.

As for concentration I believe the school's are 5% error, which again isn't great but it will have to do. Unfortunately waste will not be accepted by my teachers and they don't want several dm(3) of solution lying around. I will try and make as large quantities as they will allow (probably 250cm(3) for each electrolyte), using a volumetric flask.

Your physical problems are very interesting and I have never come across any of them before. I theorise with random radio pickup I may have fluctuating values of milivolts and therefore I should take an average of these. As for the other two, I do not believe there is much I can do to minimise these with the equipment I have (and with the level of accuracy I have will these matter?). Nevertheless you have given me many topics which sound fascinating and I will look into contact potentials especially. 

As for results, I cannot hope to get completely theoretical values due to systematic errors such as concentration and resistance. However as they are systematic, although my graph my have a slightly incorrect gradient and y-intercept, I should find a trend similar to that of the nernst equation.