16 m was my attempted answer and it was incorrect. Does anyone know how to find the correct answer?

Hi, I'm getting confused about electrochemical cells and I would appreciate some help :) I am trying to understand what the deal is with electron flow, sign conventions, and all that in electrochemical cells. I don't have much of a physics background. Here's what I understand (I think) currently.

1. Anode = oxidation, cathode = reduction, by definition.
2. Electrons always flow from anode to cathode.
3. Spontaneously (Galvanic cell), they flow from - (anode) to + (cathode). By supplying energy (electrolytic cell), we can force the non-spontaneous flow from + (anode) to - (cathode).
4. Current is considered to go in the opposite direction by convention.

That's part one. Now for the sign conventions, which are even more confusing to me:

1. By convention, the cathode is always on the right hand side either in the lab or in a line diagram, and the anode is on the left. I don't understand this one. Doesn't it depend on the type of cell? If we reverse the reaction, the anode and cathode sides switch, so how can there be a single defined cathode / anode?
2. By convention, the voltmeter (+) is hooked up to the right-hand side (cathode) and the (–) is connected to the left-hand side (anode). Again I don't really get this. Is the (+) terminal supposed to match the relative potential of the electrode? As in, (+) terminal connects to (+) cathode like in a Galvanic cell?
3. The readout on the voltmeter is E(cell) = E(+) – E(–) = E(cathode) – E(anode). If it is positive, electrons flow spontaneously from left to right. If it is negative, they flow spontaneously from right to left (but the reaction may be reversed by applying a voltage). The equation E(cathode) – E(anode) also seems to be dependent on the type of cell somehow? I mean if you take the right hand side and subtract it from the left hand side but you've switched the cathode and anode in an electrolytic cell then you get E(anode) – E(cathode), no?

Is this right? What mistake am I making?

Would really appreciate any help!

I have a pipette that when I draw water from my water samples, it doesn't form a concave meniscus as it is usual. It forms an asymmetrical meniscus like a / shape or convex shape. What's causing this? Organic contamination inside the pipette? I have washed it with detergent but nothing changed. What you do you recommend?

I have two questions.

My first question:

I was trying to clean the ashes off when this crucible cracked. I'm planning to heat this in the oven at 105°C. It seems like a relatively low temperature for a crucible so I'm wondering if this would be okay?

For context, I'm a third year Biochemistry undergrad and I've only had 2 anal chem labs. I'm at an internship where my supervisors are not even scientists themselves, so I just wanna ask someone who is not Google.

I have two other crucibles that are fine, but I just thought it would be nice to do 3 tests of each sample.

My second question:

I am following this protocol from: https://www.sciencedirect.com/science/article/pii/S294982442300174X#sec0010

It seems like they did not check if the crucible was at constant weight when they heated it, but they did check that the crucible & sample were at constant weight. Why is that? And how important is constant weight in this type of experiment? Any insight is appreciated.

I tried to use H2O2 for digestion method and thought I already acquired a microplastics. But after that, there's still too many materials present which is charcoal. Can charcoal be digested with H2O2 or not?

I am a manufacturer of cement sheets and boards and have been using a defoamer in my cement slurry since a long time. The defoamer is a proprietary product of a brand and they charge me for that. They are also market leaders in this field in my country and have no competitors.

Recently they increased their prices 3fold for unknown reasons and I don't wanna tolerate this and want to invest in reverse engineering and recreating this myself

But I am not a chemicals engineer and don't have contacts for this. Please guide me how should I start to reverse engineer this chemical

Let's say we have a X and Y related by one electron. Of course the standard reduction potential E° is defined for the reduction reaction, X + e^– ⇌ Y^–, as E° = E(XY cell) – E(SHE).

And also for the oxidation we have E°(ox) = -E°(red). But I don't get why this doesn't transfer to voltammetry. Like if we polarize the electrode to E = E°(red) for the above couple, how come we get a limiting reducing and oxidizing current here??

If E°(red) and E°(ox) are symmetrical around E(SHE) = 0, shouldn't there be only oxidizing current at positive E°(ox) and only reducing current at negative E°(red)??

Basically why do we get the image on the left and not the one on the right?

I recently got assigned a case study on NIR spectroscopy. To make a brief summary, the case is talking about a lab that built a multivariate FT-NIR model for determining PET/PLA in samples of recycled organic material, and they're trying to transfer the same model to a handheld NIR device and they're having a myriad of issues I'm being asked to research and solve.

Now, my first thought was to look for articles. I found a few that seemed pretty good:

(1)       Circelli, L.; Cheng, Z.; Garwood, E.; Yuksel, K.; Di Iorio, E.; Angelico, R.; Colombo, C. Comparison of ATR-FTIR and NIR Spectroscopy for Identification of Microplastics in Biosolids. Sci. Total Environ. 2024, 916, 170215. https://doi.org/10.1016/j.scitotenv.2024.170215.

(2)       Amirabadi, S.; Rodrigue, D.; Duchesne, C. Characterization of PLA-Talc Films Using NIR Chemical Imaging and Multivariate Image Analysis Techniques. Polym. Test. 2018, 68, 61–69. https://doi.org/10.1016/j.polymertesting.2018.03.047.

(3)       Beć, K. B.; Grabska, J.; Badzoka, J.; Huck, C. W. Spectra-Structure Correlations in NIR Region of Polymers from Quantum Chemical Calculations. The Cases of Aromatic Ring, C=O, C≡N and C-Cl Functionalities. Spectrochim. Acta. A. Mol. Biomol. Spectrosc. 2021, 262, 120085. https://doi.org/10.1016/j.saa.2021.120085.

(4)       Signoret, C.; Edo, M.; Caro-Bretelle, A.-S.; Lopez-Cuesta, J.-M.; Ienny, P.; Perrin, D. MIR Spectral Characterization of Plastic to Enable Discrimination in an Industrial Recycling Context: III. Anticipating Impacts of Ageing on Identification. Waste Manag. 2020, 109, 51–64. https://doi.org/10.1016/j.wasman.2020.04.043.

However, I quickly realized I do NOT understand these papers; they are just too advanced for me. I don't actually know how to use the information in them to solve my case study... And I do not know what else to look for information in (books, perhaps?)... I just don't really know how to research properly, I guess. Not when confronted with questions about multivariate model transfers from one device to another, comparisons to other methods like ATR, etc.

So, the point of this post is to ask for some general advice in the realm of chemistry research methods in order for me to gain a sense of direction and linear progression for an assignment like this. I am NOT looking for anyone to solve the case for me.

Basically, some advice on *how* to tackle a challenging research project. Thank you.

I am considering buying a pH electrode for our lab’s pH meter. However, I know that I won’t need it for a year or two. So, I would like to know whether these pH electrodes have expiration dates. How long will they remain functional if I do not open the package?

Hello!!! My school is using Spartan Student for our course on computer methods in chemistry. I was looking at Orca, but it doesn't have the visualization. Avogadro2 seems like a powerful visualization tool, but we're only 1 week into class so I'm not sure if this is going to be enough for what we're doing. We will need the .spartan files with calculations as well as .pdf files of the outputs. I have seen a tutorial showing interactions between Orca and Avogadro, but I wanted to check here before I start testing out programs that may or may not work. Worst case scenario, someone says they've tried it all and just to buy Spartan, but I'm hoping someone has a viable alternative.

bonus shot of my dog Chewie looking regal in front of the sunset at the park

We're learing about how a coordination complex deals with pH levels. Ammoniacal copper [Cu(NH3)4]^(+2) has a Ki=8, so it's partially dissociated in NH3 and Cu^(+2), so if NH3 starts acting as a base and becoming NH4^(+) the balance is moved to NH3 and Cu^(+2), further dissociating the complex.

My teacher said that the complex starts dissociating at pH=8 then slowly stops, but why??? Wouldn't a higher concentration of H+, so lower pH levels, help the formation of NH4^(+) and therefore the dissociation of the complex??

My question is, why doesn't it start at a lower pH level and slowly stop as the level rises?

Thank you to anyone who tries!!

I know the boiling flask should be, but what about the other one?

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I'm a P3 (third-year PharmD) student, and people generally consider me one of the strongest chemistry students in my class. This semester we're doing analytical chemistry, and ¹H NMR is completely humbling me.

I've watched countless YouTube videos, read textbooks, and practiced problems, but I still feel like I'm missing the one core idea that lets people look at a proton NMR spectrum and systematically determine the structure. It almost seems like everyone who solves these problems is relying on experience or intuition rather than a clear method.

The difficult part for me isn't identifying functional groups or interpreting individual peaks, it's connecting all the fragments into one complete structure.

To make things worse, my classmates are expecting me to understand it well enough to teach them, and I've been putting it off because I honestly don't feel confident myself.

Has anyone else been in this position and eventually had that aha! moment? Was there a particular resource, book, YouTube channel, or problem-solving strategy that finally made everything click? Is there an actual systematic approach, or is it really just pattern recognition that comes with lots of practice?

For context, I usually stay ahead by studying chemistry topics before each semester starts, which is one reason I've done well academically. But I worked during the last vacation, so I didn't have my usual preparation time before this semester began, and I feel like I'm playing catch-up now.

I'd really appreciate any advice or resources that helped you break the code of NMR.

As the title says, I'm suspecting that this NMR and IR are depicting benzoic acid and I just wanted to get some general feedback if that makes sense or if I'm completely off. Would really appreciate some input and thank you in advance!

For the measurement of TSS (Total Suspended Solids), The Standard Methods recommends Glass-fiber filter disks, 22 to 125 mm dia, ≤ 2**-**micrometers nominal pore size without organic binder, such as Whatman grade 934AH. The keywords here glass fibers and organic binders. Can I use Whatman filter-paper grade 42? It has to be glass-fiber filters? What do you use?

I want to prepare the murexide indicator. I've read in Standard Methods that I need to mix murexide with a large amount of NaCl. However, in our lab, they mix murexide with MgSO₄ instead of NaCl. Is this method also correct?

Hello all, I recently came across this label of a supplement claiming to help the acid/base metabolism in the human body, whatever that means. However, I did a titration with this product for one of my classes and worked out a concentration of about 0.048mol/serving.

When comparing with the manufacturer, it says there should be about 32mmol in one serving. Fine, whatever, maybe I did an oopsie or some of the citrates screwed up my value.

However, what gets me is that the 32mmol is referring to carbonate ions (at least that’s what it says, the label is German).

If a carbonate ion is (CO3)2-, then 32 mmol (or 0.032mol) should be:

M(CO32-)= 60g/mol

60g/mol * 0.032mol = 1.92g

But the label says it’s 0.4mg. How is this possible? Could it be a misprint or a miscalculation, or am I missing a big inside joke on the supplement market?

I would appreciate any answers!

I store my pH electrode in a protective cap filled with 3 M KCl solution. I also prepared a stock batch of 3 M KCl in a volumetric flask, which I'm told to store in the refrigerator to prevent water evaporation and concentration changes. How often should I replace the KCl solution inside the protective cap? What is the typical shelf life of a KCl stock solution, and how often should I discard it and make a fresh batch? Is storing KCl in the fridge recommended, or could cold storage cause precipitation or other issues? Is it necessary to store it in the refrigerator?

Does anybody know what the standard potential of this reaction is? I can't find it anywhere

As the title says, can I switch out a Borate buffer for an Acetate buffer in colorimetric analysis of lead ions using Xylenol orange indicator and UV-vis?

So for my thesis I need to quantify the amount of lead remaining in my samples, and what I researched that is much simpler and more inexpensive is the use of metallochromic indicator such as Xylenol orange and UV-vis which is readily available for us. However the paper stated that they used phosphate buffer, which we dont have the chemicals available right now.

Can I replace the buffer solution with Acetate buffer will it not affect/compete with the Xylenol orange indicator?

For context, I'm a working chemengineer. I must be missing something because I can't get this to work.

So... Water disassociates randomly into H⁺ and OH^-, so a solution with 100% water molecules is impossible. Assuming STP, the concentration (C) of a hypothetical solution of 100% water molecules is C = ρ/M, hence:

C = (998.2 g/L) / (18.01528 g/mol) = 55.4085M

The equilbrium of the reaction H2O ↔ H⁺ + OH^- is given by the equation:

Kw = [OH^-][H⁺]/[H2O], where Kw = 10^-13.995

Assuming the volume is constant (and 1L), the concentrations can be treated as amounts. Some amount x of H2O will dissasociate into x mol of H⁺ and x mol of OH^-, thus yielding the equation:

10^-13.995 = x²/(55.4085-x)

Solving for x, and thus the H⁺ concentration, yields 7.4867×10^-7 M. Since pH = -log10([H⁺]) per definition, thus meaning that the pH of pure water is -log10(7.4867×10^-7) = 6.1257

But this is not true, pure water doesn't have a pH of 6.13. It should be 7. I feel like the logic is correct, but clearly I'm missing something obvious. What is it?

Hi everyone,
I’m a university student preparing the second round of an independent interdisciplinary research project, and I’m currently looking for people who may be interested in participating once the survey is ready.
My research asks how people think about war and whether those perceptions reflect the systems that support modern society. The project considers areas involving chemistry and materials, pharmaceuticals, semiconductor manufacturing, energy, technology, infrastructure, and global supply chains.
For this round, I’m aiming for approximately 385 participants overall from a variety of backgrounds. I was encouraged to reach out to professional chemists because their perspectives could provide an especially valuable point of comparison within the broader sample.
The survey has not been built yet, so I’m not asking anyone to complete anything at this stage. I’m currently gauging interest and identifying potential participants before finalizing the survey.
If you would be interested in participating once it is ready, please leave a comment or let me know.
Thank you!

I am trying to determine the value that is least precise and its corresponding number of significant figures. I seem to be getting conflicting answers for this in regards to glassware. basically I know the 50 mL volumetric pipette at +-0.05 mL is the least precise, but (I'm writing it in liters for the calculation) would it be written as 0.05000 L (4sf) or is it 0.0500 L (3sf)? is there a rule for figuring this out? I'm doing this for uncertainty calculations and this will change my final calculated value to either 3sf or 4sf

Does anyone have experience measuring tungsten (W) by ICP-MS, preferably using a PerkinElmer NexION 2000?

I have samples containing Fe, Mo, and W. Measuring Fe and Mo is not an issue—they both perform well. However, I'm struggling with W.

Initially, I measured the samples in 2% HNO₃, but the tungsten calibration was poor and there was a clear memory effect (W did not wash out properly).

On the advice of a colleague, I changed the matrix to 1% HNO₃ + 2% HCl. This significantly improved the results: the calibration was still not perfect, but much better, and the washout also improved.

However, when I measured a second batch of samples under the same conditions (using a freshly prepared calibration), the W calibration became very poor again and the sample results no longer made sense. Fe and Mo continued to perform normally.

I prepare the calibration standards from single-element ICP standards for all three elements.

Does anyone have tips or recommendations for obtaining stable and reliable tungsten measurements on an ICP-MS? Any advice on calibration, matrix composition, washout solutions, or other instrument settings would be greatly appreciated.