Questions tagged [concentration]

The concentration characterizes the composition of a mixture with respect to the volume of the mixture. There are mass, amount, number and volume concentrations. Related and within the scope of this tag are normality, molality, mole fraction/ratio, mass fraction/ratio.

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Should I round an experimentally determined reaction order to an integer?

For a lab experiment I did, I calculated the reaction order for one of the reactants using data from two trials, both rates, and the concentration of that reactant during each. $$ \frac{\text{Rate}_1}{...
Caesium-133's user avatar
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What does the equilibrium constant mean for reactions with very small concentrations?

When you calculate the equilibrium constant for a reaction with a higher concentration of reactants, the answer is fairly intuitive. For example, for the reaction: $$\ce{A + B <=> C}$$ when we ...
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What does “at%” mean and how it differs from “mol%”?

Sorry if my question is a bit obvious, but for some reason I'm getting confused with the percentages in this question: Concentration of $\ce{A}$ is $\pu{80 at\%}$ and concentration of $\ce{B}$ is $...
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Calculating volume ethanol in an fermented aqueous solution of sucrose, water, and ethanol

I've been working on a biology experiment where I calculate the fermentation yield of yeast under various light induced stress responses inhibiting the translation of various fermentation enzymes. My ...
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Does real-world gas phase chemistry use "concentration reaction quotients" (K_c)?

As a theoretical chemist, my entire exposure to reaction quotients and equilibrium constants ($Q$ and $K$) is through thermodynamics ($\Delta G^\ominus = - RT \ln K_{eq}$ and so on). So as I started ...
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What is the goopy substance that forms before CaCO3 precipitates?

I do a lab where we mix a solution of sodium carbonate with a solution of calcium nitrate. As expected, calcium carbonate (white solid) precipitates out. However, if the concentration is high enough, ...
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Diffusion of particles across a plane surface

A relatively viscous material is coated with a thin film consisting of gold nanoparticles that can diffuse into the material. We can assume that all particles have a diameter of $\pu{25 nm}.$ Coating ...
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A physical meaning of the Danckwerts boundary condition in terms of concentration profile (adsorption)

Can someone please explain to me in a simplified way, what exactly does a well-recognized Danckwerts boundary condition do to the concentration profile of adsorption phenomena? I just cannot find a ...
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Is the active mass of every solid and liquid taken to be unity?

I learnt from my textbook and the question/answer - Why is active mass of a pure solid or liquid always taken as unity? that active mass of a solid or liquid is taken to be unity as: $$[A]=\frac n V=\...
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Why does the electrical conductivity increase as the temperature decreases?

I am measuring the dependence of electrical conductivity of ( NaCl and $\ce{CH3COONa}$ solutions with concentration 9g/L) with temperature using conductivity meter. Theoretically the conductivity ...
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Common ion effect

Let $\ce{HA}$ ($x$ molar) be a strong electrolyte and $\ce{HB}$ ($c$ molar) — weak electrolyte. As $\ce{HA}$ is strong electrolyte, it dissociates completely: $$ \begin{array}{lcc} \ce{&HA &-&...
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Calculating total volume mixing NaCl and water

I'm (as a non chemist) trying to calculate the the volume of a NaCl solution. The problem is that I know the volume of water prior to mixing in NaCl, but I want to know the volume of the solution ...
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What's the actual difference between Formality and Molarity?

Today, I came across a question: "State the differences, in not less than 5 points, between Formality and Molarity". Using my knowledge, I wrote down 2 points, and stretched it to 3 somehow, but that'...
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Should residual sodium be considered in measuring sodium content of sweat?

I read an article, "Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis", which describes the design of a wearable band that detects various components in sweat in ...
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ppm as hexane/propane/methane etc

This question is primarily related to stack testing data. Whenever stack testing is being conducted and the parameter being measured is VOC concentration, it is often reported as ppm (as hexane) or ...
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What is the easiest way to concentrate a solution without causing it to hydrolyze?

I’ve been working with iron acetate solutions in dilute acetic acid (vinegar) and I’ve been running into a problem. Every time I try to boil off the solvent the solution hydrolyzes to form iron oxides....
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How are gravimetric analyses of particulate matter performed, in order to determine particulate matter concentration in air?

I've been surfing Google Scholar a bit and learned that a common and comparatively less expensive method of measuring particulate matter concentration in air was analysis through gravimetric methods. ...
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Molarity 1% ammonia solution?

I have a stock solution of 25% ammonia, with a density of 910 g/L. I used this to make a 1% ammonia solution by mixing 20 mL 25% ammonia into 480 mL distilled water with 5.84 g NaCl (0.2 M), density ~...
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Will ethanol precipitate lipid-saccharide compounds?

I have a cell-free solution of culture broth. It contains a wide range of compounds ranging from salts (marine broth), lipids, and proteins to polysaccharides. My goal is to extract all type of ...
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Salt extraction from water without affecting mercury concentration

I am looking to theoretically bio-analyze a water sample regarding its mercury concentration from both sea and lake water using a biosensor with an enzyme biorecognition element. However, a big issue ...
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How would I find what specific wavelength I need to measure for a specific chemical in spectrophotometry (calcium perchlorate)?

I am currently doing a research project, and for it, I would like to use a photospectrometer to find the concentration of Calcium Perchlorate in my sample solutions. My current method of data ...
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Plotting second order reaction with different reactants

In a laser flash photolysis experiment, $\ce{C6H5NH2}$ $(C_0 = \pu{60 \mu M})$ is oxidize to its corresponding radical cations. There are three possible reaction pathways for the formation of the ...
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Why does the molar conductivity plot behave this way?

On the left image.. we see that specific conductivity is increasing at a decreasing rate, eventually plateauing as it reaches a maximum. I am unable to reconcile this with the molar conductivity graph ...
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Is 18:82 a valid ratio for aqua regia?

Here it writes that nitrohydrochloric acid (possibly Aqua Regia) is of the ratio of $18:82$, which is $1:4.56$ in a simpler form. On Wikipedia and every other source i found the ratio $1:3$. So what's ...
Lord Commander's user avatar
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Activity of a chemical species and compound

While reading a book on Instrumental analysis by Skoog, in appendix part they explain activity of a species. The relationship between activity of a species and it's molar concentration $[X]$ is given ...
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The pH of a drop of water containing ammonia

Presented with the following equations: What would the $\mathrm{pH}$ of a drop of water be, while in equilibrium with $\ce{NH3(g)}$ at a concentration of $\pu{150 ppb}$? $$\ce{NH3_{(g)} + H2O_{(l)} &...
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Calculation of resultant pH

A solution with $\mathrm{pH}=4$ is mixed with a solution with $\mathrm{pH}=10$ in equal volumes. Calculate resultant $\mathrm{pH}$. Please note both solution consists of strong acids and/or bases i....
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Given Kd find equilibrium concentrations of the reactants

$$\ce{Biotin + Avidin → Complex}$$ Biotin is a vitamin derivative that binds extremely tightly to avidin (a protein found in egg white) with a $K_\mathrm{d}$ of $\pu{1e-15 M}$. If you make a $\pu{2 mL}...
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Emergence of Lognormal distribution for the concentration of chemical compounds

I'm currently reviewing the literature about lognormal distributions describing/approximating the variability of a given chemical compound across different cells/ samples etc etc. The main argument ...
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Calculate concentrations in a system made up of molecules in order to calculate ionic strength

I understand how to calculate ionic strength where there are concentration data in molality or molarity units available and where the system is made up of only two components. However, I have been ...
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How to convert from ppm to ug/m3 in case of PMx?

For $\text{PM}_{10}$, $\text{PM}_{2.5}$ sensors, sensitivity, minimum and maximum recordable concentrations are generally expressed in $\pu{ppm}$ (parts per million) while legislation uses $\pu{\mu g /...
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NIOSH 7300 - ICP OES calculation

need some help with NIOSH 7300 method https://www.cdc.gov/niosh/docs/2003-154/pdfs/7300.pdf I have two 37mm cellulose filter paper, one is my filter blank while other is sample. The sample has 80L of ...
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Should the concentrations in weight % of the components of a solution always add up to 100%?

There's a paper with this statement of a alkaline solution: Nanostructured CuO films were formed by immersing the cleaned tabs into a hot $(\pu{96 \pm 3 ^\circ C})$ alkaline solution composed of $\...
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Is 70% ethanol hygroscopic?

I'm currently doing some DNA extractions and I realized that in some protocols, they are saying that ethanol is hygroscopic. In this source, they are saying: 85% ethanol made with nuclease free ...
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How to determine concentration limits of a buffer that's limited by solubility?

I need to maintain a certain range of % of ionisation from a buffer. For e.g. Histidine buffer. When making high concentration of this buffer at (say) pH 7.2, 25'C, [concentration] is limited to 75mM ...
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le chateliers principle

One of le chateliers principle is effect of concentration change : When the concentration of any of the reactants or products in a reaction at equilibrium is changed , the composition of ...
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What is the difference between concentration and effective concentration?

What exactly is effective concentration in simple terms? From what I can understand it is the 'real' concentration taking part in the reaction instead of the concentration of the solute. Also, if I am ...
geo's user avatar
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What concentration (M) of citric acid should I use in a titration with 0.02M LiOH?

I am using an automatic titrator that records the amount of acid/base added and the pH of the solution in the form of a graph. I am trying to titrate citric acid to capture all 3 pKas in this graph. I ...
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What are the methods used to measure the concentrations of these anions?

Chromate and dichromate anions has the following equilibrium in acidic solution: $$\ce{2CrO4^2- + 2H3O+ <=> Cr2O7^2- + 3H2O}$$ How can one experimentally measure the concentration of each ion ...
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pH, conc vs activity

After studying a somewhat overview of "gamma" activity coefficient (it is not actually in our course but may come in exam as a part of unknown paragraph in ionic equilibrium) I can understand most ...
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Absorbance vs titrant added in acid-base titration

I was working on this question: Nitrophenol is a colorless weak monoprotic acid ($\mathrm{p}K_\mathrm{a} = 7.2$) whose conjugate base is bright yellow. To $2.00\ \mathrm{mL}$ of a solution of $...
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Method for increasing concentration of extracts

I am using reagent grade propylene glycol (99.9% pure) and vegetable glycerin (99.7% pure) separately as solvents to extract certain active essential oils/molecules of various plant flowers. The ...
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Coffee and orange juice concentrations with a twist

This question dates back to a time where I used to watch something called The Curiosity Show... Kinda like Bill Nye the Science Guy's show. I just can't recall the answer to this so I'm hoping that ...
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Preparing CdSe electrodeposition bath

What is the best way of preparing an aqueous solution containing 5 mM $\ce{CdSO4}$, 1 mM $\ce{SeO2}$, 0.5 M $\ce{Na2SO4}$ and adjusting pH to 3 by adding 0.5 M $\ce{H2SO4}$? What is the ...
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What is the correct method for converting a concentration given in ppm to molarity?

I need to convert a concentration of dissolved boric acid $(\ce{H_3BO_3})$ in water (at high temperature and pressure) from ppm to mol/L. Concentration of boric acid: $c_{ppm}=1500\ \ce{ppm}$ Molar ...
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How to calculate the pH of a mixture of an acid with a buffered solution?

Being a physicist by training, having worked in software development for the last 10 years. Having heard my last chemistry lecture 15 years a go I am a bit lost in regards to how one can calculate the ...
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"Is there any library in Python or software for analyzing raw chromatography data?"

I have taken the data directly from the FID sensor using a DAQ, so I have the chromatography data in this format: (2 data colummns in a txt file) (18000 rows) Time (s) Intensity (V) 0.00367___0.0008 ...
user138375's user avatar
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Buffer solution of NaH2PO4 and Na2HPO4

We have this exercise without solutions From a 0.2 M $\ce{NaH2PO4}$ solution and a 0.2 M $\ce{Na2HPO4}$ solution, a buffer solution with pH = 6.8 is to be prepared. The total concentration of $\ce{...
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Can you use more concentrated hydrogen peroxide solution for obtaining iodine from PVP-I?

In NileRed — Making iodine video Nigel Braun extracts iodine from the medical povidone-iodine. He says that the quantities of hydrogen peroxide needed is $\pu{500 ml}$ of $3\,\%$ hydrogen peroxide. I ...
Itamar Cohen's user avatar
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Is the wavelength of light generated through a chemical reaction independent?

The chemical reaction in question is the reaction between Luminol and hydrogen peroxide. Is the wavelength of light generated through this reaction dependent on the concentration of either reactant? I ...
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