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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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How can I calculate number of moles introduced into the ractor? [duplicate]

-''- From avarge reaction rate? For example I got avarge reaction rate equal to 0.0005 mol/dm^3*s and substrate concentraction equal to 0.8M
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1answer
11 views

Types of concentration units

I would like to ask about a concentration unit. What does it exactly mean when stock concentration of something is, for example, 5X? Thank you in advance!
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What is the concentration of H2 for the equation H2+I2=2HI if the equilibrium constant is 64 and the initial concentrations are both 1.9

So for this, I set up the equation = $$64= \frac{(x)^2}{(1.9-x)^2}$$ I took the sqrt of both sides and got $$8=\frac{x}{(1.9-x)}$$ So then I did $$8(1.9-x)=x$$ And simplified I got $$15.2=9x$$ ...
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0answers
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Help with my lab please! [on hold]

For my lab, I am changing the concentration of 1-hexene and hydrogenating it. The issue is, I was going to find rate of reaction, but I don't know how to monitor the time, so i don't think finding the ...
11
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1answer
479 views

Is there a name for this algorithm to calculate the concentration of a mixture of two solutions containing the same solute?

There is an algorithm called "Mischungskreuz" (German for "x of mixing") that is sometimes taught as a shortcut to figure out the following problem: You have two solutions that contain a solute at ...
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1answer
20 views

How do I make 100 milliliters of 100mM H2O2 using 3% H2O2? [on hold]

I need to make 100 milliliters of 100mM H2O2 using 3% H2O2. Do I: add X milliliters of distilled water to the 3% H2O2? How many ml? or add X milliliters of 3% H2O2 to the distilled water? How ...
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25 views

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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1answer
43 views

Is 99% Isopropyl Alcohol sold in stores really 99%?

My understanding is that an azeotropic mixture of isopropanol and water is 91%. This makes sense as to why there are so many brands of rubbing alcohol sold at 91%. There are also some sold as 99%, ...
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0answers
16 views

Calculating 'Air Dilution' Concentration to Estimate Final Odor Intensity [closed]

Air flows at a rate of 1 l/min into a closed 40ml flask containing 2ml of amyl acetate serially diluted to 0.000002143% v/v concentration. The air-gas mixture then has the opportunity to escape trough ...
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2answers
35 views

Help required for the calculation of moles [closed]

If 4.5ml of yeast prep + 0.5ml of 0.25 M glucose is separated into 2ml in 2 similar flasks. How many micromoles of glucose are there in one flask? Using M1V1=M2V2 (0.5ml/1000)*0.25M = M2 * 2ml = 0....
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1answer
44 views

how to calculate the initial concentration of NaOH in a mixture? [closed]

I have doubts about how to find the equation for the calculation of the initial concentration of $\ce{NaOH}$. I have the following information: in the kinetic study of a reaction, We measure $\ce{20....
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1answer
34 views

Direction of mass transfer in two film theory

In an extraction process compound A is transferred from one solvent to another solvent. The two solvent may be, for example, water and dichloromethane. These two solvents are immiscible and when ...
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1answer
68 views

Diffusion across a thin film

Given this concentration profile, I am to (1) determine at which side substance A will diffuse out of the membrane and (2) chose one of the following profiles below which represents the concentration ...
2
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1answer
44 views

Calculate pH of a buffer solution

Calculate the pH in a buffer prepared from $\pu{50 mL, 0.30 M}$ formic acid ($\ce{HCOOH}$) and $\pu{30 mL, 0.40 M}$ sodium formate ($\ce{HCOONa}$). My way of solving: $n_{\ce{HCOOH}} = 0.05 \times ...
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1answer
27 views

What are some ways to measure sugar concentration of fruits? [closed]

I've tried to do titrations using the quantitative Benedict's Solution and it was difficult to use as I do not have a way of keeping a constant temperature. I am currently using a Polarimeter to find ...
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2answers
826 views

Why proton concentration is divided by 10⁻⁷?

I am reviewing the book Biochemistry Concepts and Connections by Appling, Cahill, and Mathews and I cannot understand why they divide by the hydrogen concentration by $10^{-7}$. Why not just leave it ...
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1answer
34 views

Measure the concentration of lactose in dairy products [closed]

I would like to measure the concentration of lactose in various dairy products : milk, cheese, yoghourt... How is it done in labs ? How can I do that using cheap equipments ? Thanks
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3answers
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An aqueous solution of NaCl has a mole fraction of 0.21. What is the mass of NaCl dissolved in 100.0 mL of solution? [closed]

Work mole fraction of NaCl = 0.21/0.21+0.79 If there is 1 mol of total solution, there will be 0.21 mol NaCl and 0.79 mol H2O 0.21 mol NaCl = 12.27 g 0.79 mol H2O = 14.23 g this would yield a ...
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1answer
33 views

What is the molecular weight of Tris(ethylenediamine)cobalt(III) iodide pentahydrate? [closed]

What is the molecular weight of Tris(ethylenediamine)cobalt(III) iodide pentahydrate ? The chem formula is: (Co(en)3(I)3*5(H2O) According to my calculation, it is: 928.77 g/mol. But I am ...
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3answers
81 views

Conversion from a PPB value to µg/m3 of Isobutylene

I have a quite simple problem, found a lot of information about it, but I am not sure anymore if I do my calculations right. I own a sensor, which reports measurements in isobutylene units as PPB. So ...
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2answers
56 views

final concentration

Cheers. I am doing a hands on lab for intro to Chemistry. I basically have to do something seemingly simple. I pour 8.0 grams sugar, weighed, into a volumetric flask that is volume of 25mL. I add 15mL ...
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1answer
34 views

How do I get a 20% ratio of sodium bisulfate with 1 gallon water? [closed]

How many lbs do I add to 1 gallon of water to get a 20% sodium bisulfate ratio? I am in the middle of anodizing some aluminum.... I just threw the whole 3 lbs in... hopefully it works... I ended up ...
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1answer
171 views

What does x mean in (1-x)A – xB composite materials, molar ratio, weight ratio or volume fraction?

I've been collecting data about ceramic materials and often I get to see composite materials are described as $(1-x)\ce{A} - x\ce{B}$. I am confused what this $x$ means. And I haven't seen any of the ...
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2answers
52 views

Molarity and equilibrium reactions Kc [closed]

Samples of $\ce{A}$ ($\pu{1.40 mol}$) and $\ce{B}$ ($\pu{0.80 mol}$) are placed in a $\pu{2.0 L}$ container and the following reaction takes place: $$\ce{2 A (g) + B (g) <=> C (g) + D (g)}$...
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1answer
81 views

What is the molar enthalpy of reaction

When 0.45 g of Zn is added to 50.0 ml of 0.95 M HCl solution, the solution inside the calorimeter heats up by 12 °C. What is the molar enthalpy of the reaction (in kJ/mol)? I know how to find the ...
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2answers
53 views

When making a calibration curve, do we have to use the wavelength at maximum absorbance?

If you are making a calibration curve for $\ce{CuSO4}$ where you plot absorbance against concentration, does the wavelength have to be exactly at the maximum of the peak? Or can it be somewhere else ...
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0answers
15 views

Does the starting concentration in a isochoric container depend on the pressure?

Given is the following reaction of carbonic acid and carbon dioxide: $$\ce{RCOOH (g) → RH (g) + CO2 (g)}$$ The reaction rate of this decarboxylation was measured in a container with constant volume ...
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1answer
22 views

Determining the concentration after half-life period

I was given the reaction In diluted solution and with neutral pH, the reaction reacts according to a reaction velocity law of pseudo-1. order: $$-\frac{dc_{DNPA}}{dt}=k_{obs},\quad k_{obs}=k\cdot c_{...
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1answer
23 views

Can I have a homogeneous 2 molal solution of copper(II) sulfate at 20 °C?

I'm doing a high school chem project where I am making a calibration curve of copper(II) sulfate for spectrophotometry in which I make solutions with five different concentrations. The most ...
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2answers
114 views

Finding mole fraction from molality

Calculate the mole fraction of ammonia in a $\pu{2.00 m}$ solution of $\ce{NH3}$ in water. What I know is that the formula for mole fraction is $$X = \frac{\text{no.-of-moles-of-solute}}{\text{(no.-...
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1answer
20 views

How to find concentration of three species from given molar absorptivities [closed]

If I am given the molar absorptivities of three species at a given wavelength, and I only have the concentration of one of those species, how can I determine the concentrations of each of the ...
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0answers
47 views

What is the maximum concentration of HNO3 (nitric acid) which may be handled outside of a hood?

Commercial stock solutions of HNO3 (nitric acid) are usually 70% w/w, and according to several MSDSs (e.g. here), it is dangerous to inhale it: Symptoms/effects after inhalation : Irritation ...
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1answer
43 views

Confusion between moles and molarity units

I am a total newbie in the field and i would like some kind of guidance. So, I have been recently given 2 datasets with measurements regarding several phospholipid fatty acids of plasma HDL. Both ...
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1answer
24 views

How does the concentration of a gas affect the entropy of a system in a chemical equilibrium?

The question asks about factors that increase the entropy of the system. The mark-scheme states that "decreasing the concentration of a gas without changing the volume of the container" is the answer. ...
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1answer
36 views

What is PPM in terms of air concentration?

When they say the $\ce{CO2}$ concentration is $\pu{350 ppm}$ what does this actually mean? Does this mean that if we took a sample of air say $\pu{1 m3}$ then $\pu{350 mg}$ of that cubic meter would ...
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1answer
86 views

Does molarity change if you decrease volume?

For example if the solute of the solution contains $\pu{0.5 mol}$ and the total volume is $\pu{0.5 L}$, the molarity would be $\pu{1M}$. But if I take a portion of that solution, let's say $\pu{0.1 L}$...
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1answer
72 views

How to derive rate law expression for inversion of sucrose with changing pH?

I came across a question worded as follows- "The inversion of cane sugar proceeds with half life of 50 minutes at pH=5 at any concentration of sugar. However, if the pH=6, the half life changes to 500 ...
3
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1answer
36 views

Homemade spectrophotometer to exemplify Beer-Lamberts law

I have built a 12-band spectrophotometer, and i'm currently keen on proving Beer-Lamberts law through a small practical example. The solution that I'm going to test with my spectrophotometer, is ...
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1answer
53 views

Diluting topical cream (10%)

I need to dilute a face cream with 10 % active ingredient to 2.5 % and 5 % but I am confused as to how. I looked into the $$c_1V_1=c_2V_2$$ and $$\text{concentration of a solution}=(\text{amount of ...
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1answer
681 views

Acetic Acid % in vinegar? Given average molarity of acetic acid

Question: The stockroom claims the percent acetic acid in vinegar to be $2.0\%$. The density of vinegar is $\pu{1.106 g {mL}-1}$. Using average molarity given ($\pu{0.2844M}$) calculate the mass ...
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1answer
57 views

How to determine the volume of water necessary to produce a solution with 4.9 g/l sulfuric acid?

The molar mass of sulfuric acid is $M(\ce{H2SO4}) = \pu{98.1 g/mol}$. We have $\pu{100 mL}$ of a $0.1$ molar solution of sulfuric acid. What volume $V$ in $\mathrm{mL}$ of water, $\ce{H2O}$, do we ...
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2answers
195 views

Is the mole fraction equal to the weight fraction?

Whenever there is a reaction is excess of air it is customary to assume mole ratio of $\ce{N2}$ to $\ce{O2}$ as $79/21$. However, in another reaction which states that it will contain $\pu{1 wt\%}$ of ...
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1answer
85 views

How to determine the proton concentration in the following solution in mol/L? [closed]

A $\pu{0.8L}$ solution contains $\pu{0.60 g }\ce{ NaOH}$ in water. Then the above question follows. It's been a long time that I made some chemistry exercises. Now I'm stuck with a couple of ...
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1answer
123 views

should charge balance be based on activities?

We have a fluid with $\pu{0.01 M}~\ce{HCl}$ and $\pu{0.02 M}~\ce{K2HPO4}$, so if we assume activity coefficients are $1$ throughout we can find pH as $6.800012$ and confirm that at that pH there is ...
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1answer
77 views

Maximum Concentration of Benzene possible

A question for my PhysOrg course states: Assume you are performing a reaction in which benzene is a reagent. What is the maximum concentration of benzene possible? Hint: what facts do you need to ...
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1answer
30 views

How many samples would be worth when following a desorption? How to relate with limit of detection?

I am following the desorption of a compound from a polymer. Let's imagine that it occurs at a certain rate and most of the compound is desorbed after 5 days (as in the figure). Then, I could use many ...
2
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1answer
57 views

Why does water diffuse from a lower solute concentration to a higher one?

I'm studying biology and this came up in the context of passive transport. I understand why, in general a gas moves down a concentration gradient (the random movement of gas particles and probability)....
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1answer
903 views

When using a “dilute hydrochloric acid” solution, how diluted should it be?

Quite often when reading through some instructions or documentation or an outline that I've found online (EG: acid-base extractions), theres a step that involves using a "dilute hydrochloric acid ...
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1answer
159 views

Calculate mass concentration of Ca(OH)2 solution

Can anyone help me calculate the mass concentration of $\ce{Ca(OH)2}$ solution with molar mass $\pu{74.1 g/mol}$ at the $\pu{pH of 12.8}$. My work so far: From the pH I get the molar concentration ...
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1answer
51 views

Amount concentration versus number concentration

The IUPAC Gold Book defines Amount concentration Amount of a constituent divided by the volume of the mixture. Also called amount-of-substance concentration, substance concentration (in ...