# Tag Info

### 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, ...

### 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 ...
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### 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,...
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### 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-\...
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### 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,...
• 41
Accepted

### How and when do redox indicators work?

It is fully analogical to pH indicators and acid-base titrations. The potential of the equivalence point should lay within the potential range of indicator transition. The optimal case is when the ...
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### Role of MnSO4 in permanganometric titration

Both the oxidating ion $\ce{MnO4-}$ and reducing ion $\ce{C2O4^2-}$ are anions and therefore electrostatically repulsing each other, what makes their reaction slow. $\ce{Mn^2+}$ ions serve as catalyst,...
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### 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 ...
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### I need help for my chloride titration

The common titration methods are explained here https://en.wikipedia.org/wiki/Argentometry Check to see what is available in the lab [That might also give a hint to the method you are supposed to use....
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1 vote

### Determination of Calcium from a mixture of calcium and magnesium using Back Titration

The general reactions are described very well here: https://chem.libretexts.org/Ancillary_Materials/Laboratory_Experiments/Wet_Lab_Experiments/General_Chemistry_Labs/General_Chemistry_Labs/...
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1 vote

### How to determine the dynamic of progression of two simultaneous precipitation (double replacement) reactions?

Consider that solubility of $\ce{AgCl}$ is 1.9 mg/L and of $\ce{Ag2CrO4}$ is 22 mg/L, both at 25 °C. When just a little $\ce{AgNO3}$ has been added, the $\ce{Ag2CrO4}$ is not concentrated enough to ...
• 33.2k
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 ...
• 33.2k
1 vote

### I need help for my chloride titration

You could add an aliquot to your conical flask and add a few drops of acetic acid and dichlorofluorescein indicator along with some dextrin solution. You can then titrate against silver nitrate ...
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1 vote

### Does dilution of titrant gives a more accurate result?

The use of a burette in titration, once considered an art, has nearly disappeared from modern educational practice in schools and universities. This decline is due in part to the lack of expertise in ...
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1 vote

### How is indigo carmine used in Lowenthal-Permanganate titration as a redox indicator?

After the endpoint of this titration you have an excess of permanganate, so your indicator is going to be oxidized, not reduced. It is confusing because most everything you find about indigo carmine ...

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