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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 do I tell what the chemical composition of a rock is? [closed]

I love to look at rocks, they are so fascinating, but I always find myself wondering how many of each kind of atom are in this particular rock, or how many atoms in total. The only thing I can tell is ...
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1 answer
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Concentration of spectator ions halves?

I have a question below that I'm not too sure about. A precipitation reaction is caused by mixing 100mL of 0.25M $\ce{Na2Cr2O7}$ with 100 mL of 0.25M $\ce{Pb(NO3)2}$. The precipitate is filtered from ...
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5 answers
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Molarity into Mole Fraction

So, recently, I was solving a question wherein I had to find out an equation connecting mole fraction to molarity. We have to express the mole fraction of the solute ($x_2$) in terms of molarity (M), ...
1 vote
2 answers
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How would I find the molarity/concentration of a gas using pV = nRT?

The problem I'm working on is: At $\pu{1100 K}$ and a total pressure of $\pu{1 atm}$, $\ce{SO3}$ is $75.0\%$ dissociated. $$\ce{2SO3(g) <=> 2SO2(g) + O2(g)}$$ Assume $\pu{1.00 mol}$ of $\ce{SO3}...
3 votes
1 answer
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What happens during electromigration in low concentration electrolytes?

I'm not sure if my understanding is correct, please correct me if there is something wrong. Considering a 2 electrodes system with a constant voltage applied between both electrodes and with no ...
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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}{...
1 vote
2 answers
154 views

How does the concentration of H+ ions in HCl change as the pH changes? [closed]

I am helping my friend's 16 year old prepare for her GCSE chemistry exam. This question was on an AQA GCSE Chemistry past paper but I do not know the year and could not find a markscheme for it on the ...
8 votes
1 answer
710 views

What happens to an ongoing electrolysis when you turn off the battery?

Suppose you do an electrolysis experiment, where you have two carbon electrodes, a battery, and water in a which a strong electrolyte, like NaCl, is dissolved. The circuit is closed and the ...
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Calculating mass of a solution

I am trying to calculate the mass of a specific volume of glucose 5% solution. I calculated the values for the components of the solution and wanted to seperately calculate the mass of the solution ...
-5 votes
1 answer
75 views

Different method of solving a question giving different answer [closed]

Calculate the concentration of nitric acid in moles per litre in a sample which has a density, $\pu{1.41 gmL^–1}$ and the mass per cent of nitric acid in it being $69 %$. I attempted to consider a 1L ...
2 votes
1 answer
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Deriving Nernst Equation for a hydrogen-oxygen Fuel cell

Reading across electrochemistry books (particularly the fuel cells chapter of the book "Alternative energy systems and applications" by Hodge) I came across the following formulae: $$\Delta ...
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1 answer
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Determine reaction concentration at chemical equilibrium with multiple reactions

I have a problem understanding how to calculate the change/dependence of the concentrations at the chemical equilibrium using multiple reactions. The concentration of my reactants and products at ...
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Find the pH of a solution obtained by mixing 100 ml 0.1m Na3PO4 and 100 ml 0.1 M NaH2PO4. Given that H3PO4: [Κα₁ = 10^-4, Κα₂ = 10^-7, Каз = 10^-11] [closed]

So, my query is that since NaH2PO4 is a weak acid, and Na3PO4 is a basic salt, wouldn't they react? Another theory was that since NaH2PO4 is a weak acid and Na3PO4 is a salt of strong acid and NaH2PO4,...
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1 answer
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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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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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Acid base titration molar ratio [closed]

Consider the following neutralisation reaction: $$ \ce{2HNO3 + Ba(OH)2 -> Ba(NO3)2 + 2H2O} \tag{1} $$ I would be glad for help in how to solve this problem with $c_1V_1 = c_2 V_2$, because the ...
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1 answer
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Mass of gaseous ammonia required to prepare ammonia solution of a given pH

How many grams of gaseous ammonia do you need to make $\pu{200 mL}$ aqueous ammonia solution with $\mathrm{pH} = 11.34?$ As the mole ratio is the same for $\ce{H+}$ and $\ce{NH3},$ $$\ce{NH3 + H+ -&...
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1 answer
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How do I explain that voltage decreases when increasing the concentration of the cathode in a voltaic cell?

I just finished a lab experiment in which I built a voltaic cell with copper (II) sulphate and zinc sulphate. My experiment was to identify the correlation between the concentration of copper (II) ...
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How to calculate theoretical value of mass output using electrolysis with different electrolyte concentrations?

I am writing a research paper on a zinc-copper electrolysis experiment observing the mass output of Zinc on a copper cathode, in which I am changing the concentration of the zincsulfate electrolytic ...
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1 answer
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Cesium Chloride Density Gradient Centrifugation and Isotopes

In Cesium Chloride Density Gradient Centrifugation, as used by Meselson and Stahl, Cesium ions can be seen as strongly affected by centrifugation, so much so that they can overcome their ionic bonds ...
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Will increasing the initial concentration of a reactant result in more time for the reaction to go to completion?

I understand that increasing the concentration of a reactant increases its instantaneous reaction rate, but shouldn’t the amount of time for the overall reaction to go to completion increase? For ...
1 vote
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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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1 answer
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Determining the concentration of ammonium nitrate by chemical means

I have several litres of ammonium nitrate solution that I do not know the concentration of, but is approximately 0.6M. I don't have precise enough instruments to determine it via its density. I ...
1 vote
1 answer
163 views

Iodine solution concentration

I am planning to make 1L of 0.005M iodine solution from KI and I2. I have found instructions that say to use 2 g of KI and 1.3 g of I2 but no explanation why exactly this particular amount. I also ...
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1 answer
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How to convert molar volume to volume?

This seems like a simple question that people must have asked already, but I can't find an answer online. I'm not a chemist, but need to use a code that deals with thermodynamics. I am trying to use ...
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1 answer
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Convert daltons (Da) to molar mass (g/mol) [duplicate]

This is probably a stupid question... In converting Da to molar mass (g/mol), Since 1 Da = 1 g/mol, is it logical that 64,776 Da = 64,776 g/mol or am I missing an intermediate calculation? Thank you!
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Units of Activation Energy

Consider the reaction $$\ce{aA + bB -> cC + dD}$$ whose reactants are given by A and B and the products are C and D. Say the activation energy of this reaction is some $x$ joules/mole, But moles of ...
4 votes
3 answers
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Molar Absorptivity of Copper(II) Sulfate

What is the molar absorptivity of copper sulfate? I am trying to find the molarity of copper sulfate solution by absorption in a spectrophotometer with a cuvette. However, I can't find $\varepsilon$, ...
1 vote
1 answer
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Creating 1L of 1000 ppb stock solution of Pb2+

I’m testing on samples that require a concentration of 1000 ppb (or 1 mg/L) of Pb 2+. My first thought was to simply dissolve 1 mg of Lead nitrate in 1 L of deionized distilled water to create 1 L of ...
1 vote
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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 ...
3 votes
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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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Concentration term PPM [duplicate]

What volume do we assume when the concentration is written as mass by volume ppm? I mean when mass by volume percentage is say 20%, we can say that 20g solute is present in 100 ml solution. So if it ...
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Determining whether precipitation will occur or not and finding the concentration of a specific ion in a solution

The Ksp value of AY2 = 9.148 x 10^-2. I am having problem with calculating the concentration of ions. And without the correct concentration I can't find the Qsp/Kip so I'm stuck without them I can't ...
7 votes
6 answers
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Best regression model for a sigmoidal pattern

Students submit the data for an acid–base titration to my app. The abscissa axis corresponds to the volume. Along the ordinate axis are the pH values. The curve I’m looking for must work automatically ...
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1 answer
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Determination of the chloride concentration by the modified Volhardt method

Would someone help me solve a task: The concentration of chloride ions in aqueous solutions can be determined by the Volhardt method. An excess of silver nitrate is added to the sample containing the ...
3 votes
8 answers
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Why is the specific gravity of 0.9 % saline 1.0046?

Medical Normal Saline (0.9% Saline) contains 9 g of salt dissolved in 1000ml of water. Hence a litre of NS should weigh 1.009 kg. Hence its specific gravity should be 1.009, but it’s only 1.0046. (I'...
1 vote
1 answer
110 views

A silly doubt on the concept of volume percent and concentration

I am trying to solve the following elementary problem of volume percent, however, I am not quite sure where my mistake is: Ethanol has a volume-by-volume concentration of 93.3%. Calculate the volume ...
3 votes
1 answer
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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 ...
2 votes
1 answer
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Equilibrium Solubility of CO2 in Aqueous Solution and its Dependence on H3O+ Concentration

The equilibrium solubility of $\ce{CO2}$ in an aqueous solution is given by three chemical reactions: $$ \begin{align} \ce{CO2(g) &<=> CO2(aq)}\label{rxn:R1}\tag{R1}\\ \ce{CO2(aq) + H2O &...
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1 answer
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Are all salts completely dissociated in solution when put in smaller amounts than their molar solubility?

From what I understand, the solubility is given in terms of molar solubility (or $\pu{K_{sp}}$), from which it can be easily calculated). Indeed, the saturation point represents the maximum amount of ...
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Is it a convention to divide rate of reaction by stoichiometric coefficient?

If we consider a reaction $$ \ce{A + B -> 3 C} $$ The rate of reaction is given by $$ R= -\dfrac{\Delta[A]}{\Delta t} = -\dfrac{\Delta[B]}{\Delta t} = \frac13\dfrac{\Delta[C]}{\Delta t} $$ I know ...
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1 answer
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Relationship of acids and bases with pH. (Proportional Relationship) [duplicate]

Can someone please clarify the relationship between acidic-basic strength and pH? I have come across conflicting information and am unsure about the correct understanding. Some people including my ...
1 vote
1 answer
102 views

Scrubbing methanol and ethanol from a gaseous mixture

I have a gaseous mixture (air) at a temperature of approximately 30 degrees Celsius in which the following gases are present: Oxygen 0 - 25% Carbon Dioxide 0 - 20% Methanol 0 - 100 ppm? Ethanol 0 - ...
17 votes
1 answer
7k views

How to interpret parts-per notations? 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 ...
1 vote
2 answers
507 views

How to prepare solution of liquid reagent of the given molar concentration?

I have a liquid reagent with molecular mass $M = \pu{294.08 g mol^-1}.$ I'd like to prepare $V = \pu{400 ml}$ of solution of that reagent with a concentration $c = \pu{100 mM}.$ Does it mean I have to ...
1 vote
2 answers
13k views

Titration with Ca(OH)2

In the laboratory, $20.0$ milliliters of an aqueous solution of calcium hydroxide, $\ce{Ca(OH)2}$, was used in a titration. A drop of phenolphthalein was added to it to indicate the end point. The ...
-4 votes
1 answer
191 views

Dilution formula for NH3 solution [closed]

I need this for an experiment: ca. 3 mL concentrated (15 M) aqueous ammonia solution, NH3 (from a dropping bottle.) I have the NH4OH pictured below. How can I dilute it to get what I need? What is the ...
-2 votes
3 answers
731 views

Why do we have to prevent the hydrolysis of iron(III) nitrate?

I want to make particular concentration of ferric ions from $\ce{Fe(NO3)3.9H2O}$, and then I found this video It says that we have to add nitric acid to prevent iron from hydrolysis, what does it mean?...
-2 votes
1 answer
179 views

How does an equilibrium move when increasing the concentration of water?

I have the following equilibrium given: $$\ce{[Co(H2O)6]^2+(aq) + 4 Cl-(aq) <=> [CoCl4]^2-(aq) + 6 H2O(l)}$$ (I imagine the (l) for water is wrong, as the water is a part of the solution) The $\...
4 votes
1 answer
124 views

Chemical species equations in a kinetic mechanism of combustion

In combustion, for a kinetic mechanism involving $m$ reactions and $n$ chemical species, of the form \begin{align} \begin{cases} \nu_{11}' \mathcal{S}_1 + \nu_{12}' \mathcal{S}_2 + \dots + ...

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