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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30
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2answers
132k views

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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1answer
2k views

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 ...
14
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1answer
343 views

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 ...
13
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4answers
70k views

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. ...
13
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1answer
589 views

What was the lithium concentration in 1940's 7-Up?

I just came across this article in the New York Times, where lithium (or more correctly, lithium salts), a known anti-depressant had been added to beverages in the 1940's. They also mention that a ...
12
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2answers
2k views

What is the point of using molality when we have molarity?

Molality and molarity are both concentration terms. Given molarity's popularity molality seems rather antiquated. Why is molality still discused in modern chemistry classes?
12
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3answers
14k views

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 ...
11
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1answer
644 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 ...
11
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2answers
2k views

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 ...
11
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1answer
157 views

Etymology of “normality”

Why the concentration of a solution expressed in gram equivalent weights of solute per litre of solution is termed as "normality" ? Does it have anything to do with the word "normal" ?
10
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21k views

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 ...
10
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1answer
35k views

How do I calculate the concentration of sulphuric acid by a titration experiment with sodium hydroxide?

In my latest chem lab the objective was to create a primary standard of $\ce{NaOH}$ and use it to determine the concentration of sulfuric acid. The first part of the lab was determine the molarity of ...
10
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4answers
6k views

Why do solutions become saturated?

Why can a solvent dissolve only a particular amount of solute? If we add more solute to the solution, the number of solute particles in contact with water increases. So rate of dissolution should ...
9
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3answers
510 views

Why is the equilibrium constant defined that way intuitively?

Suppose we have chemical equation: $$\ce{ aA + bB <=> cC + dD }$$ then equilibrium constant is defined: $$K=\frac{[C]^c[D]^d}{[A]^a[B]^b}$$ but why don't we define it as: $$K=\frac{cd[C][D]...
8
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2answers
1k views

What is the difference between chemical equilibrium and dynamic equilibrium?

Is chemical equilibrium and dynamic equilibrium the same thing? Both point to the reversible reactions and no net changes in the concentrations of product and reactant. Dynamic equilibrium from ...
8
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2answers
857 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 ...
8
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2answers
3k views

Why is hydrochloric acid often sold as 33% concentration?

What is the historical perspective for the choice of 33% concentration that is often found in commercial sales of Hydrochloric acid? Is this the same reason we find sulfuric acid sold at 37% and ...
8
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1answer
51k views

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: ...
8
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2answers
1k views

How to find the mass of the solute given a concentration as a mass fraction?

Formalin is a $37\%~\mathrm{W/W}$ solution of methanal in water. What mass of water must be added to $250~\mathrm{g}$ of methanal to make formalin. Here's what I've done so far. It's wrong though. ...
8
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1answer
207 views

How should I modify my molecular dynamics simulation so that known chemical reactions can be modelled?

I have written some molecular dynamics code that I want to use to model known chemical reactions. By known I mean that it has been observed in a lab that $\ce{A +B->C}$. I am not interested in ...
7
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508 views

Relation between moles, molar mass and mass

You are asked to prepare a 0.8500 M solution of aluminum nitrate. You find that you have only 50.00 g of the solid. What is the maximum volume of solution that you can prepare? I'm confusing my ...
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2answers
3k views

Alkaline glycine buffer molarity

Having never prepared a buffer solution before, I am hoping for a little help in understanding the process. This method I plan to use calls for a $\pu{0.1M}$ glycine buffer at pH $10.6$. Some ...
6
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4answers
421 views

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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3answers
357 views

Why is the ionic product of water not divided by the concentration of water?

I know the ionic product of water is $[\ce{H+}][\ce{OH-}]$, by following the equation: $$\ce{H2O <=> H+ + OH-}$$ But actually it's just another way of writing: $$\ce{2H2O <=> H3O+ + OH-}...
6
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1answer
535 views

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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3answers
2k views

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 ...
5
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3answers
6k views

Why is Ka constant when volume is increased?

The following graph shows $\ce{Ka}$ vs ${V}$ (Volume) at constant temperature, as ethanoic acid is diluted: However, I thought it would instead produce the following graph (see below). $\ce{Ka=[...
5
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3answers
19k views

Temperature dependence of molarity and molality

My textbook informs me that Molarity is dependent on temperature, whereas molality is not. I'm aware of the definitions of both molarity and molality, but consider this scenario: A solution of $\...
5
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1answer
244 views

Calculating the mass of acceptable carbon monoxide in a room

The acceptable concentration of $\ce{CO}$ in the air is $10\:\mathrm{mg/m}^3$. In a room that is $19\:\mathrm{m\times4.0\:m\times25\:m}$, what is the acceptable mass in kilograms of $\ce{CO}$? ...
5
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2answers
12k views

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 ...
5
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2answers
680 views

How to convert P2O5 concentration to H3PO4 concentration?

Why are some elements such as phosphorus reported as $\ce{P2O5}$ concentrations when the materials have no $\ce{P2O5}$ in them. I would like an explanation of how the conversion is done between real ...
5
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1answer
2k views

What's the relation between molarity and molality?

I am trying to derive the relation between the molarity and molality of a solution Mole concept $\displaystyle n = \frac{M'}{M''}$ Here, ($n$) stands for number of moles $\ce{(M^{'})}$ stands for ...
5
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1answer
119 views

Optical techniques for kinetics studies

What optical methods can be used to measure the concentration of reacting gases in a reactor during an exothermic and fast reaction? I need to monitor and measure the local concentration of my gases (...
5
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1answer
739 views

Estimate the concentration of HCl and volume of 6 M HCl required to complete precipitate each of the given salts

In our chemistry lab we performed the following experiment below. Given that $K_\mathrm{sp}(\ce{AgCl}) = 8.2 \times 10^{-11}$ and $K_{\mathrm{sp}}(\ce{PbCl_{2}}) = 1.7 \times 10^{-5}$ ...
5
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1answer
12k views

What is a complete reaction?

For a lab assignment, I combined $\pu{10 mL}$ of $\pu{1 M}$ sodium sulfate solution with $\pu{10 mL}$ of $\pu{1 M}$ calcium chloride solution. The ionic equation I came up with is: $$\begin{multline} ...
5
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1answer
1k views

Is the density of the solution significantly different from the density of the solvent?

I am working on a mathematical model for the dissolution of coffee in water. I need to know some precise details about the effects of dissolution on the density of the mixture of the substances (that ...
5
votes
1answer
4k views

How to calculate the concentration based on dilution of a stock solution?

One of my exam questions is about lipstick and calculating the amount of lithium in the lipstick by AAS. The determination took place by making standard solutions with known concentrations of lithium. ...
4
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2answers
6k views

How to increase the concentration of HCl

Today I have purchased some $\ce{HCl(aq)}$ on my local market with a concentration of 23%. However, I need to obtain a concentration of 37% in order to perform an experiment. Can I use distillation ...
4
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1answer
3k views

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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2answers
14k views

CuCl2 dissolved in water

We dissolve $10\ \mathrm{g}$ of $\ce{CuCl2}$ in $0.1\ \mathrm{L}$ of water. Given that: $M(\ce{Cl})=35.5\ \mathrm{g/mol}$ $M(\ce{Cu})=63.5\ \mathrm{g/mol}$ How can one calculate the molar ...
4
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2answers
490 views

How to determine if two calibration curves are parallel, within 5%

I have complex matrices and I need to make sure the matrix does not affect the measurement of my analyte. To do that, I need to prepare samples of my analyte in a solvent and of the matrix reinforced ...
4
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1answer
4k views

What is the lethal dose ( LD50 ) of coffee?

Of course, there are many types of coffee, so I would like a range of lethal dose amounts for the average human, from the mildest of lattes to the most hardcore of espressos. Pure caffeine's lethal ...
4
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1answer
88 views

Finding ppm getting too big of numbers

I have a question that is to find the concentration of magnesium ion in ppm for a $0.025\ \%$ solution of $\ce{MgCl2}$. I can use this formula: $$\text{concentration in ppm} = \frac{\text{mass solute}...
4
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1answer
3k views

How to interpret the instruction of the dilution of hydrogen peroxide?

I am required to prepare $\pu{120cm3}$ of hydrogen peroxide to each of one of my students tomorrow. Some material is given to me on the method of preparing the solutions. Within the method of ...
4
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2answers
1k views

Percentage purity of Ba(MnO4)2 sample that completely reacts with given H2O2?

$\pu{40 g}$ $\ce{Ba(MnO4)2}$ (mol. wt. = 375) sample containing some inert impurities in acidic medium is completely reacted with $\pu{125 mL}$ of $\pu{3 M}$ $\ce{H2O2}$. What is the percentage purity ...
4
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1answer
293 views

Why does the conductivity of a LiOH solution decrease when boric acid is added?

If I start with pure water and add $\ce{LiOH}$ the conductivity of solution increases. However, if I then dissolve boric acid in the same solution the conductivity falls. I would have thought adding ...
4
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2answers
266 views

NaClO Concentration

In my previous occupation the usage of bleach--$NaClO$--I found was quite staggering, and based off of the health issues that I and other coworkers were having, I wanted to see how close we were ...
4
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1answer
191 views

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 ...
4
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1answer
447 views

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 ...
4
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1answer
123 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 ...