Skip to main content
13 votes
Accepted

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

This is a very good question! I'm not sure why you received a downvote. What you are asking about is called a polarization current. Suppose we are electrolyzing a solution and suddenly we stop the ...
ACR's user avatar
  • 41.2k
11 votes

Best regression model for a sigmoidal pattern

It looks like your model is not complete. The current shape of your model makes the function go to zero for small values of $x$. There is nothing to indicate that the function should go to zero, ...
AccidentalTaylorExpansion's user avatar
10 votes

Best regression model for a sigmoidal pattern

Some of the examples on the page EdV's comment points to are programmatic (as in: knowledge of a scripting/programming language is beneficial/a requirement) in addition to statistics. If you are more ...
Buttonwood's user avatar
  • 30.1k
8 votes

Best regression model for a sigmoidal pattern

I am answering to the comment that you made to the @Buttonwood's great answer. Clearly the $y$ values are the $\text{pH}$ of the solution and the $x$ values the volume of base added. If you don't mind,...
Metal Storm's user avatar
  • 3,546
6 votes

Best regression model for a sigmoidal pattern

The best regression after (automatically) surveying your data is Pearson IV with five parameters (a, b, c, d, e). Thanks to Buttonwood for digitizing your data. $$ y=a \frac{\left[1+\frac{\left(x-\...
ACR's user avatar
  • 41.2k
5 votes

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

The amount concentration (molar concentration, molarity) is defined in IUPAC Gold book as: $$c_\mathrm{solute}=\frac{n_\mathrm{solute}}{V_\mathrm{solution}}$$ Practical procedure is: Add solvent to ...
Poutnik's user avatar
  • 42.4k
5 votes
Accepted

Deriving Nernst Equation for a hydrogen-oxygen Fuel cell

Rather than pointing whether the assumptions are correct or incorrect, I will show you a general method to obtain the Nernst's equation for any system. It is a more systematic and formal approach, ...
Metal Storm's user avatar
  • 3,546
5 votes

A silly doubt on the concept of volume percent and concentration

First of all it is a stupid problem. Volumes don't add. So 90.00 ml of ethanol and 10.00 ml of water doesn't yield 100.00 ml of solution. The problem messes up significant figures. 10 L and 93.3% ...
MaxW's user avatar
  • 22.3k
5 votes

Convection or Advection term in the Absolute flux of a chemical species

The term advection in transport phenomena is generally introduced in the definition of material derivative of a scalar magnitude $B$ is \begin{equation} \frac{\mathrm{D}B}{\mathrm{D}t} = \...
Metal Storm's user avatar
  • 3,546
4 votes

How to convert molar volume to volume?

If you have given the molar volume $V_\text{m}$ in $\pu{cm3 mol-1}$, the molar amount in $\pu{mol}$, you get the volume as $V = n \cdot V_\text{m}\ [\pu{cm3}] = 0.1 \cdot n \cdot V_\text{m}\ [\pu{J ...
Poutnik's user avatar
  • 42.4k
4 votes

Best regression model for a sigmoidal pattern

The generalised logistic function might be a good fit for your data. You will probably have to test the effects of each parameter to determine whether you need them to model your data. At first glance,...
aaueer's user avatar
  • 41
4 votes

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

@ Pono. Your two propositions are both wrong. You must introduce $11.76$ g solute in a volumetric flask having a volume of $400$ mL (which is not easy to find by the way). Then you add $300$ or $350$ ...
Maurice's user avatar
  • 28.9k
2 votes

Equilibrium Solubility of CO2 in Aqueous Solution and its Dependence on H3O+ Concentration

General solution of such systems is solving a set of $N$ nonlinear equations for $N$ variables. There are concenctrations of $\ce{H+}$, $\ce{OH-}$, $\ce{CO2(aq)}$, $\ce{H2CO3(aq)}$, $\ce{HCO3-(aq)}$, $...
Poutnik's user avatar
  • 42.4k
2 votes

Best regression model for a sigmoidal pattern

Use the R drc package which was created to solve your problem exactly: sigmoid regression; its acronym stands for Dose Response Curve. It is a well-established package backed up by scientific ...
Niels Holst's user avatar
2 votes
Accepted

Cesium Chloride Density Gradient Centrifugation and Isotopes

The ratio of masses of 135Cs to 137Cs is smaller, by a factor of 5, than the ratio of masses of 14N to 15N. While what you suggest is theoretically possible, the thermal motion of water, which must ...
DrMoishe Pippik's user avatar
2 votes

Different method of solving a question giving different answer

Your answer is correct, although a more direct calculation would be: $C_i=y_iC=\frac{x_i\require{cancel} \cancel{M}}{M_i}\frac{\rho}{\cancel{M}}=\frac{\left(0.69\right)\left(\pu{1410g/L}\right)}{\pu{...
Sam202's user avatar
  • 1,654
2 votes

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

What is the concentration of H+ ions in a solution of hydrochloric acid with pH 2.5? Using the definition of pH $= -\log(\frac{[\ce{H+}]}{\pu{1 mol L-1}})$, you can easily calculate this as long as ...
Karsten's user avatar
  • 40.8k
2 votes

Molarity into Mole Fraction

Just for completeness - there are multiple equivalent ways how to reach the desired result. One is Starting with the defining equation for the target quantity Continuing by substitutions using ...
Poutnik's user avatar
  • 42.4k
1 vote
Accepted

Molarity into Mole Fraction

I think your path to the final answer is wrong in some aspects of your thinking process (e.g., look Poutnik's comment). Since you have put enough effort to solve this problem yourself, I'll try to ...
Mathew Mahindaratne's user avatar
1 vote

Molarity into Mole Fraction

Let: A = Solute B = Solvent $$X_A=\frac{C_A}{C}=\frac{C_A\;M}{\rho}=\frac{C_A\;\left[M_A\;X_A+M_B(1-X_A)\right]}{\rho}=\frac{C_A\;M_A\;X_A+C_A\;M_B-C_A\;M_B\;X_A}{\rho}$$ $$X_A\left(\rho+C_A\;M_B-C_A\;...
Sam202's user avatar
  • 1,654
1 vote

Molarity into Mole Fraction

$M = n_2/V$ $x_2 = \frac{n_2}{n_2 + n_1}$ Mass of solution: $M_1n_1 + M_2n_2$ Volume: $M_1n_1 + M_2n_2/ \rho$ Let moles of solution be 1, i.e., $n_1 + n_2 = 1$. $M = \frac{x_2\rho} {M_1(1-x_2) + ...
entropy's user avatar
  • 99
1 vote
Accepted

What happens during electromigration in low concentration electrolytes?

If we consider no Faradaic reactions happening on either electrode then all you will have is a capacitor. Imagine you have some mobile ions in solution, then these ions will feel an electric field and ...
Noah's user avatar
  • 352
1 vote

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

This question changes a simple definition of: [pH = the negative logarithm of the hydrogen ion activity in M/L], into a puzzle or possibly an IQ test. Knowing nothing about pH the relationship between ...
jimchmst's user avatar
  • 2,223
1 vote

Determination of the chloride concentration by the modified Volhardt method

Ok, your formula for calculating the chloride concentration: $$[\ce{Cl^-}] = \sqrt{\frac{K_\text{sp}}{[\ce{Pb^2+}]}}$$ is fine as far as it goes. The equation can give a ballpark estimate of the ...
MaxW's user avatar
  • 22.3k
1 vote
Accepted

Determining the concentration of ammonium nitrate by chemical means

As long as the solution is pure, your idea of making standardized $\ce{NH4NO3}$ solutions and comparing conductance should work. Caveat: This works as long as conductivity vs. concentration is a ...
DrMoishe Pippik's user avatar
1 vote

Iodine solution concentration

$\ce{I2}$ has a molar mass of $254$ g/mol. $\ce{KI}$ has a molar mass of $39 + 127 = 166$ g/mol. Then $1.3$ g $\ce{I2}$ is $\frac{1.3}{254} = 5.12$ millimole $\ce{I2}$. Also $2$ g $\ce{KI}$ is $\frac{...
Maurice's user avatar
  • 28.9k
1 vote

How would I find the molarity/concentration of a gas using pV = nRT?

I'm only reviving this old question because I got significantly different results compared to the proposed answer. Let: A = $\ce{SO3}$ C = $\ce{SO2}$ D = $\ce{O2}$ The change in moles for this ...
Sam202's user avatar
  • 1,654
1 vote

Molar Absorptivity of Copper(II) Sulfate

TL;DR: the values that you may find online will most likely only be accurate up to a few percents. I would strongly encourage the use of a reference solution of known concentration that you can ...
mranvick's user avatar
  • 536
1 vote

Are all salts completely dissociated in solution when put in smaller amounts than their molar solubility?

We should not expect salts with multiply charged ions to be completely dissociated in aqueous solution except, perhaps, at very low concentrations. The comments refer to magnesium sulfate, a technical ...
Oscar Lanzi's user avatar
  • 59.1k
1 vote
Accepted

Scrubbing methanol and ethanol from a gaseous mixture

Try a trap filled with a high boiling point liquid, such as glycerol or propylene glycol, which would absorb the organic gases... but would require periodic replacement or heating to drive off vapors. ...
DrMoishe Pippik's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible