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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34 views

Which conductivity law should I use to calculate the conductivity of a solution with high/low concentration?

I have a set of NaCl solutions with concentrations ranging from 0.05 M to 0.1 M. I have been trying to calculate the conductivity of these solutions and compare the obtained values with the ...
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57 views

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 ...
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1answer
54 views

Adjustment of calcium, magnesium and alkalinity in drinking water?

It's been a long time since I did any molar chemistry in school and despite doing a lot of reading on the subject this week, I am making a mess of some basic calculations. I hope that someone who ...
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1answer
313 views

Volume of 0.5 M HCl needed to make a 10 % 500 ml solution

What volume of $0.5\ \mathrm M$ HCl solution is needed to prepare a $500\ \mathrm{ml}$ $10\ \%$ concentration solution, whose density is $1.05\ \mathrm{g/cm^3}$. I've started off with finding the ...
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50 views

Molar flux through membrane

Consider a liquid of pure $\ce{A}$ covered by a composite membrane through which the vapor of $\ce{A}$ is diffusing. The membrane consists of two layers of thickness $l_1$ and $l_2$. The diffusion ...
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2answers
197 views

Molarity Numerical on Mixing Solutions

If 3 L of 1 M NaOH solution is prepared by mixing properties of stock solutions of $x$ L of 2.5 M NaOH and $y$ L of 0.4 M NaOH and no water is to be used, find $x : y$. My attempt: $$3 = 2.5x + 0.4y$...
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1answer
114 views

How do I calculate the hydronium ion concentration if I know the strontium hydroxide concentration?

This is my first question so I would appreciate feedback on how to ask better questions. Forgive me if I don't know how to properly format math/chem. The guide is confusing. I was taking a practice ...
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1answer
125 views

IUPAC Recommendations for Concentration Units (ppb, ppm)

In a recent interesting post, (Is 1 ppb equal to 1 μg/kg?) it was pointed out that IUPAC advises to abandon parts per million, parts per billion quantities and instead it suggests to employ micromole/ ...
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Is 1 ppb equal to 1 μg/kg?

In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I ...
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34 views

Preparation of Copper (II) Sulfate Pentahydrate Solution

how would you make a solution of Copper (II) Sulfate Pentahydrate to achieve 150, 200, 250 and 300 mgL−1 concentration of copper? I do not have the anhydrous version of the solute. Also, when I ...
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1answer
56 views

Changes over time in sodium hydroxide concentration in a hot water bath used for pretzel manufacture

I make soft pretzels using a hot (190 °F) and dilute (2-4% w/v) sodium hydroxide solution. The bath is kept hot in a open-top stainless steel vessel like a stockpot. I make my pretzel dough and dip ...
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95 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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653 views

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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622 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
139 views

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

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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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
155 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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2answers
41 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
71 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
61 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
114 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 ...
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1answer
409 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
182 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
850 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
80 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
515 views

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
52 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
459 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
170 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
78 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
236 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
128 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
633 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
451 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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20 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
30 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
26 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
4k 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
25 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
287 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
55 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
95 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
578 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
2k 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
263 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 ...
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1answer
58 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
288 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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3k 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
68 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
541 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 ...