# Questions tagged [ph]

pH (or the potential of hydrogen) is a scale used to measure how acidic or basic an aqueous solution is.

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### Fitting multiple pKa's

I have three histidine residues that are next to each other in a protein. When I compute the fraction of un-protonated states for each individual histidine as a function of pH my titration curve has a ...
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### How to calculate the number of protons in a sphere given the volume and the pH?

The spherical radius of a nano-droplet of a solution ($\mathrm{pH}$ of which is $6$) is given as $\pu{20nm}$. I can find the molar concentration of $\ce{H+}$ and subsequently the number of $\ce{H+}$ ...
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### How to calculate the composition of a borate buffer with a defined pH using the Henderson-Hasselbalch equation?

I am struggling with what appears to be an extremely easy pH problem that uses the Henderson-Hasselbalch equation. The problem and answer provided by the book is given below. I understand where the ...
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### Why does adding salt to water reduce the pH?

I recently heard someone claim that adding table salt to vinegar caused HCl to form which helped them clean coins - clearly not the case - however I thought I'd disprove it by doing an experiment. So ...
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### Hydronium ion concentration to compare pH values

I'm having a bit of trouble with this question: Which has a higher $\mathrm{pH}$ value, $\pu{0.001 M}$ $\ce{HCl}$ or $\pu{0.1 M}$ $\ce{CH3COOH}$ $(K_\mathrm{a} = \pu{1.8E-5})?$ I have calculated ...
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### How to calculate Revelle factor using only pH, DIC and TAlk for seawater?

I have the temperature, salinity, $\mathrm{pH},$ dissolved inorganic carbon (DIC) and total alkalinity (TAlk) values for an estuarine water sample. I want to calculate the Revelle factor. The Revelle ...
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### How to find the ionization constant of an unknown weak acid?

A $\pu{0.45 M}$ solution of a weak acid, $\ce{HX}$, has a $\pu{pH}$ of $4.5$. What is the ionization constant, $K_a$, of the acid? $\ce{[HX]}$ is already given as $\pu{0.45 M}$. $\ce{[H+]}$ is given ...
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### Impossible pH For Aqueous Weak Acid Solution

An aqueous solution of $\ce{HCl}$ has a $\mathrm{pH}$ of $0.00$ if $[\ce{H+}] = 1.00 \; \mathrm{M}$. I tried to see if an aqueous solution of acetic acid could have a $\mathrm{pH}$ of $0.00$, given ...
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### Confusion regarding calculating the pH of a salt of weak acid and weak base

I need to calculate the $\mathrm{pH}$ of a salt of weak acid and weak base in an aqueous solution. Method I used for calculation For a salt of weak acid and weak base (assuming complete dissociation ...
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### Finding pH of acid in water [closed]

How would you find the pH of an acid dissolved in water? Would you need to take the fact that the pH of water is already 7 into account and go on from there? Say, for example, that you add 0.0500 mL ...
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### Acidic and alkaline salt solutions: why do some salt form acid/bases while others don't [closed]

I have a question regarding salts and their solutions. How come some salts, like sodium carbonate and ammonium chloride, produce acids/bases when dissolved in water? Moreover, how can you predict ...
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### Why is the pH level of carbonation loss decreasing then increases afterwards?

We have done an experiment of the titration of unsealed sprite soda to find the amount of carbonic acid being loss on various duration (0 to 1 hour), due to decrease pressure. The calculation was to ...
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### Why amino acids (Zwitterion) become either negative or positive at low and high pH solutions?

The amino acids are Zwitterions. In neutral pH, an Amino acid's amino group has a postive charge and Carboxyl group has negative charge. They cancel each others charge thanks to the $Hydrogen$ that's ...
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### Peptide at pH=1

In the following peptide: I want to know the net charge of the peptide at pH=1. According to me the as the solution is acidic so every nitrogen will get protonated. Hence the number of charge = ...
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### Calculating charge of amino acids (am I doing it right?)

Please consider this picture of a peptide chain: I've done some examining on the different amino acids and concluded that the chain is as follows: Lys-Leu-Gly-Ser-Citrullin (variant of arginine). I ...
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### pKa values for amino acid

To calculate the pI value, we take the average of the pKa values from the 2 groups that result in a net charge of 0. For that to happen, the pKa values should be at the midpoint of titration where ...
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### Calculating pH of a saturated weak acid/base solution [closed]

How can you calculate the $\mathrm{pH}$ if you know for example the $\mathrm{p}K_\mathrm{a}$ or $\mathrm{p}K_\mathrm{b}$ value of a weak acid/base and how much acid/base can dilute in water. Let's ...
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### Is black tea a pH indicator?

Today, I made a cup of lemon tea in a different way than usual. Instead of pouring hot water in to a mug containing lemon juice and black tea (my normal routine), I let the tea steep for a little ...
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A $\pu{1.0 L}$ buffer solution of $\mathrm{pH}~4.43$ is made up of $\pu{0.30 M}$ sodium ethanoate and $\pu{0.20 M}$ $\ce{HCl}$ solutions. Calculate the volume of sodium ethanoate and $\pu{0.20 M}$ $\... 0answers 54 views ### Is pH in a charged hydrogel and its supernatant solution constant? Let us assume we deal with ideal systems without interactions. The gel phase and the supernatant solution phase are in thermodynamic equilibrium. The supernatant solution shall consist of different ... 0answers 76 views ### Can a universal indicator turn colorless? I learned that litmus paper could be bleached by chlorine to turn colorless. I’m wondering if any chemical substances can react with all the components of a universal indicator such that it turns ... 1answer 77 views ### Ratio of uncharged to charged side chains [closed] The$\mathrm{p}K_\mathrm{a}$of the side chain imidazole group of histidine is$6.0.$What is the ratio of uncharged to charged side chains at$\mathrm{pH}~7?$Here's my attempt to the solution: $$7 ... 1answer 65 views ### pH After Titration 50mL \ce{SO2} titrated with 0.1M of \ce{KBrO4} with reaction:$$\ce{KBrO4 + 4SO2 + H2O -> 4H2SO4 + KBr}$$The equivalent point is reached when the volume of \ce{KBrO4} is used as much 50mL. ... 3answers 22k views ### How to determine the pH of a mixture of two weak acids? We’ve two solutions: Solution 1 \ce{HCOOH} its concentration is c_1=10^{-2}\ \mathrm{mol/l} and its volume is V_1 = 50\ \mathrm{ml} and its \mathrm{pH}_1 = 2.9. Solution 2 \ce{CH_3COOH} ... 2answers 964 views ### Applying Henderson–Hasselbalch equation to amino acids: which pKa to use to calculate Z-/HZ ratio? I was wondering which \mathrm{p}K_\mathrm{a} to use when calculating the ratio of \ce{HZ} to \ce{Z-} of amino acids, the Henderson–Hasselbalch formula used:$$\mathrm{pH} = \mathrm{p}K_\text{a} ... 0answers 39 views ### How do I find pH of a mixture of weak acids? [duplicate] Suppose that we are given two weak bases$\ce{HA_1}$and$\ce{HA_2}$. We are also given the$K_\ce{HA_1}$and$K_\ce{HA_2}$. How can we calculate the$\mathrm{pH}$of the mixture? 1answer 294 views ### How do I calculate the ensemble-average net charge of an amino acid at given pH? I am given an amino acid with an ionizable side chain at a certain pH. How do I determine the net charge of that amino acid when there are mixed protonation states of one or more of the groups at that ... 1answer 174 views ### Why is maximum buffer capacity for some diprotic buffers not when pH = pKa? According to Rajkovic et al. : $$β = \frac{[\ce{H+}]}{K_\mathrm{w}} + 2.303\cdot\frac{[\ce{H+}]\cdot K_\mathrm{a}\cdot c}{[\ce{H+}] + K_\mathrm{a}}$$ where$K_\mathrm{a}$is the ... 1answer 40 views ### When there is an increase in temperature, how is the pH of the ocean affected? (Question is related to ocean acidification) This is my current understanding: Ocean acidification is the result of atmospheric$\ce{CO2}$dissolving in the ocean's water. When this occurs the$\mathrm{pH}$of the ocean decreases (from the ... 2answers 8k views ### Effect of pH on electrolysis I understand (more or less) that acidification of water helps in the dissociation of water into ions. Acids easily dissociate into ions in aqueous solution. So, accordingly, the hydrogen from the acid ... 1answer 120 views ### Understanding the increase in pH of a buffer solution upon incremental additions of NaOH analytically So let's say we have$200\ \mathrm{mL}$of$1\ \mathrm M\ce{CH3COOH}$solution. In this solution we have the equilibrium$\ce{CH3COOH <=> CH3COO- + H+}$. To that we add$100\ \mathrm{mL}$of$...
The problem asks to determine the $[\ce{H+}]$ in a $0.20~\mathrm{M}$ solution of $\ce{Na3PO4}$. The $K_\mathrm{a}$ of $\ce{HPO4-}$ was given as $4.5\times 10^{-13}$, which then allows one to calculate ...