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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What is an equivalent?

I want to know what is an equivalent and how is it different from equivalent mass. How to calculate and why is it used in chemistry for knowing concentration?
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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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Why is active mass of a pure solid or liquid always taken as unity?

Active mass is defined as the molar concentration ie. number of Gram-moles per litre. My book then wrote Active mass of pure solid/liquid is always 1 . The book reasoned that Molar ...
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What is active mass?

I'm aware of the fact that active mass is defined as the molarity of a substance, but my textbook states that "Active masses are dimensionless quantities but for our purposes we generally take them ...
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11 votes
1 answer
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Does concentration of salt increase or decrease rate of rusting?

I want to know whether increasing the concentration of salt, specifically $\ce{NaCl}$, increases or decreases the rate of rusting. There are conflicting theories that explain opposite outcomes: ...
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Why is the concentration of pure water is 55.5 mol/L?

Whilst reading about pH, it is given that concentration of water is $\pu{55.5 M}$. Let water be of $\pu{1 mol}$ at $\pu{297 K}$ and $\pu{1 atm}$ pressure. Then the concentration is $$c =\frac{n}{v} = ...
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4 compounds in equilibrium with one another - determine their equilibrium concentrations

I know that if I have two compounds in equilibrium and I know $\mathrm{\Delta G}$, then I can use $$\mathrm{\Delta G=-RTlnK}$$ to determine the concentrations of the two components at equilibrium. I ...
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What do the different grades of chemicals mean?

When purchasing chemicals from Sigma, Fisher, or wherever, there are often -grade's attached to their description like reagent-grade, technical-grade, analytical-grade, or more niche-sounding biotech-...
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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 ...
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Raoult's Law and Mole Fraction

Raoult's Law states that the partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its mole fraction in the mixture....
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What does the unit M stand for? [closed]

What does $\mathrm{M}$ signify in this pH calculation? To me, it just seems to be a random variable. For example: $\ce{[H+]} = 1.0\times10^{-7}~\mathrm{M}$ I am not sure what the $\mathrm{M}$ is ...
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What is the difference between molarity and concentration?

I learned these two words in school but still I don't understand what the difference is between them. From my understanding, molarity and concentration means the number of moles in a certain solution. ...
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What do curly brackets {} mean?

I learned that square brackets ex: $[\ce{H2O}]$ can be used to denote the concentration of water molecules in a fluid. The notation used much in equilibrium problems and such. However, sometimes I ...
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Representing woody biomass concentration for kinetic reactions

Woody biomass is composed of cellulose, hemicellulose, and lignin components. The following diagram provides representative formulas for each component: Biomass can be represented by it's density, ...
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How can a substance be diluted to nothing?

If I start with a small amount of a substance, and I dilute that substance with billions of gallons of water, what is the scientific explanation for there being no (actually zero) remaining molecules ...
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Calculating the molar mass of a solute from freezing point

A $\pu{4.305 g}$ sample of a nonelectrolyte is dissolved in $\pu{105 g}$ of water. The solution freezes at $\pu{-1.23^\circ C}$. Calculate the molar mass of the solute. $k_f$ for water is $\pu{1.86 C/...
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How to calculate molar concentration from equilibrium equations with no initial concentration given?

I have the equations: \begin{align} \ce{CO2(g) + H2O(l) &<=> H2CO3(aq)} &\quad K_1 &= 10^{-1.47} \tag{1}\\ \ce{H2CO3(aq) &<=> H+(aq) + HCO3-(aq)} &\quad K_2 &= 10^{-...
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Does the initial rate in the reaction of magnesium powder with nitric acid depend on the volume or the concentration of the acid?

For the question regarding the initial reaction rate, I don't quite understand why the answer is D. If I calculated the number of moles from the volume and conc, I would get A=0.4 moles; B=0.2 moles;...
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Whose concentration is more 1 molar or 1 molal?

I was reading about concentration terms like molarity, molality, etc. and then I came across a question: which concentration is more: 1M(molar) of solute x dissolved in water vs. 1m(molal) of solute ...
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Molar concentration calculation with absolute uncertainty

A solution of $\ce{F-}$ is prepared by dissolving $(0.0933\pm0.0004)\ \mathrm g$ of $\ce{NaF}$ $(M= (41.989\pm0.001)\ \mathrm {g/mol})$ in $156.00\pm\ \mathrm{mL}$ of water. Calculate the ...
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Why do some solutions eventually stop boiling and start "popping" as they get more concentrated?

A very long time ago I performed an experiment in my kitchen, part of which was to remove all water from a solution. Unfortunately I don't remember what was in it, but the point is that as the ...
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8 votes
2 answers
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Quantifying soapiness; there's pH, pKa and pO2, is there a p_soap or p_surfactance?

Yes, $\mathrm{pH}$ is a concentration, $\mathrm{p}K_\mathrm{a}$ is a dissociation constant, and $\mathrm{pO_2}$ is a partial pressure. These are (roughly speaking) ways to indicate how much of a key ...
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How is sulfuric acid with a concentration of 12 M also 72% w/w?

According to LabChem, $12~\mathrm{M}$ of $\ce{H2SO4}$ is $72~\mathrm{w/w\%}$. When I try to convert $12~\mathrm{M}$ of $\ce{H2SO4}$ to $\mathrm{w/w\%}$ I get $117\%$ which is obviously wrong. $$\...
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How can I calculate the molar conductivity of a solution with multiple solutes?

I'm running an experiment mixing 2 different solutions, $\pu{5 mL}$ of $\pu{0.1 M}$ $\ce{NaCl}$ with $\pu{5 mL}$ of $\pu{0.1 M}$ $\ce{KCl}$. I am measuring the conductivity of the total solution in $\...
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2 votes
3 answers
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How to convert from w/w% to molarity?

After reading a number of explanations about it after googling, I'm a bit confused on this. Some explanations are doing it using a solution density, others aren't, though most are. On one site it's ...
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Why does mercury(II) nitrate form only when using concentrated nitric acid?

In the reaction between mercury and nitric acid, mercury(II) nitrate only forms when concentrated nitric acid is heated up and added to it, if the acid is dilute, mercury(I) nitrate forms. I ...
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Solubility product of HgS

The reported solubility product of $\ce{HgS}$ is $4 \times 10^{-54}$. How is this possible? The minimum concentration that is possible is 1/avogadro's constant which shall be about $10^{-23}\ \mathrm{...
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6 votes
4 answers
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How do I create a concentrated solution of singlet oxygen (in the dark)?

Without appealing to reactions that require photons / light, how do chemists achieve a very high concentration of continually produced, though quite short lived, singlet oxygen in aqueous solution (i....
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Do I use the Nernst equation when the concentrations of electrolyte in both half cells are equal?

I'm doing a chemistry report, and for my experiment I investigated the amount of voltage produced by different half cells in a voltaic cell. However, I tested them under nonstandard conditions as ...
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How to convert ppm to g/m3?

I'm not very comfortable with chemistry and I need to convert $\ce{CH4}$ concentration values in $\pu{ppm}$ to $\pu{g/m3}$. Is that possible? I've already researched a bit and realised that for water ...
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4 votes
2 answers
803 views

Relationship between molar mass and density in solids

In ideal gases, it's pretty clear that 1 mole of gas occupies 22.4 L at STP. By knowing this, it's easy to calculate density given molar mass. However, this isn't true for solids. If I know molar mass ...
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How to determine the iron content in spinach with a spectrometer?

I used a spectrometer to find the absorbency of 5 solutions with different iron concentrations. \begin{array}{rrrrr} \ce{Fe (III)} / \pu{mol L-1} & \text{Absorbance} & V(\ce{HCl}) &...
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Molarity vs Normality in labeling sulfuric acid

Molarity (M) is defined as moles of solute per liter of solution while Normality (N) is defined as moles of reacting units per liter of solution. Most texts use sulfuric acid as an example to ...
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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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2 votes
1 answer
440 views

The effect of dilution on the rate of a system in equilibrium

I'm attempting to answer a question from my textbook, however the answer that the textbook provides doesn't make sense to me. The question: Laura, a VCE chemistry student, loves graphs and wanted to ...
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2 votes
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Up to which dilution can one assume that 1 mg/l = 1 ppm?

For aqueous solutions it is often assumed that 1 milligram per liter equals 1 ppm. Are there any guidelines up to which concentration this shortcut is admissible? Are there any formulas which ...
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2 votes
2 answers
43k views

Finding new pH after NaOH added to buffer solution

I have a buffer containing 0.2 M of the acid $\ce{HA}$, and 0.15 M of its conjugate base $\ce{A-}$, with a pH of 3.35. I need to find the pH after 0.0015 mol of $\ce{NaOH}$ is added to 0.5 L of the ...
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2 votes
0 answers
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why do solids and pure liquids have no effect on yield and equilibrium? [duplicate]

There are three parts to my question. Part one: Let's assume we have a reversible reaction at equilibrium as follows : Calcium carbonate (solid) goes into calcium oxide(solid) and carbon dioxide(...
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Can water volume reduce with introduction of another chemical [duplicate]

Can a chemical be introduced to a volume of water which can actually reduce the volume of water in that container?
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1 vote
1 answer
104 views

How to calculate concentration of a protein based on known concentration and mw of other protein

I have a Peptide A (mw = 5074Da), the table below showed measured concentration by Qubit from 5uM up to 80uM solution. All under 20uL solution. Below is the standard plot for Peptide A (not sure if ...
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1 vote
1 answer
771 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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How would one calculate the Heat Capacity Ratio for a multiple compound Gas?

So I'm attempting to calculate the heat capacity ratio (known also as adiabatic index) of a gas with several concentrations of different compounds such as N2, H2O, CO2, CH4 etc. And while I have an ...
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Confused on normallity

So normality is 'equivalents' over liters solution right? I'm having a hard time understanding exactly what an equivalent is. At first from one thing I read i thought it was just the H released from ...
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0 votes
1 answer
251 views

How to distinguish mass concentration and density?

I am writing a proof where I have to mention both with density and of a material and mass concentration (mass/volume) of a material. I am using the letter $\rho$ to represent density, and I didn't ...
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Density and concentration of hydroiodic acid [closed]

I weighted my hydroiodic acid sample: 25 ml weight 34.1 g, so the density is about 1.364 g/ml. I want to know its concentration based on density. Does anyone have the corresponding density chart?
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Rate and order of a reaction

The rate of reaction can be measured from a concentration vs time graph of a particular reactant in a reaction. But, if in your reaction you have different reactants of different orders surely they ...
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How can I convert the number of particles per liter to gram per liter

How can I convert the number of particles per liter to gram per liter? I know the size of these particle and so, I calculated the volume and then by the density I calculate the mass. After that I don'...
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Can I determine the rate law order from stoichiometric coefficients?

I've read in two books, and seen in three separate videos courses, that you cannot determine the rate law order from stoichiometric coefficients. Then, I have seen homework and "practice" problems ...
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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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