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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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Why does pKw first decrease but eventually increase when temperature rises?

I understand the initial decrease in pKw. $\ce{Heat + H2O (l) <=> H+ (aq) + OH- (aq)}$ Temperature increases, reaction shifts to the right, so $\ce{H+} \text{ and } \ce{OH}$ ...
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Slow acidification process

I'm trying to find a substitute of Glucono delta-lactone (GDL). This food additive is usually used to produce silk tofu. Because of its slow hydrolysis the pH decreases very smoothly, which results in ...
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Naming convention for buffer solutions/systems

Is there an official naming convention to follow for buffer solutions/systems? I've noticed that the name of the buffer usually just follows the name of the salt (ex. sodium acetate buffer), but what ...
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Why does saline have a pH of 5.5?

I am a physician and administer 0.9% NaCl in water ("normal saline") to patients frequently. The bag says it has a pH of 5.5 (compared to the human body of 7.4). I am asking why the pH is so low. It ...
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How can I preserve chlorophyll for long periods of time?

I'm currently working on a XIX century photographic process called Anthotype. It relies on organic colored substances that fade when exposed to sunlight. For the substances I've tried alcoholic ...
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258 views

What pH indicators are commonly used for non-polar medium?

Compounds, commonly used as pH-indicators, are soluble in aqueous media and polar solvents (DMSO, DMF, NMP etc.) and are functional pretty much across all these solvents. However, practically none ...
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How to determine concentration limits of a buffer that's limited by solubility?

I need to maintain a certain range of % of ionisation from a buffer. For e.g. Histidine buffer. When making high concentration of this buffer at (say) pH 7.2, 25'C, [concentration] is limited to 75mM ...
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Help with idea for an optical ph sensor

I am experimenting at home with the idea of making an optical ph sensor that can read the colour of ph indicator using photodiodes. I am wondering if there is some kind of ion permeable membrane ...
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Effect of protein hydrophobicity on metal interaction

I'm studying how metals and proteins interact (metal-protein complexes). I've found that almost all proteins could bind with metal at higher $\mathrm{pH}$ values, but also found some proteins showed ...
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How much hydrolysis will likely occur of the following bonds at pH 1-4 in the time period of 1-3 hours?

The bonds are: (I have given pictures of what I mean in case there's any ambiguity that I leave open in these questions. Also so that if you want to number the R groups you've got a head-start) ...
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Water values and water hardness

We have drinking water with the following values: Calcium mg/l 62.7 Magnesium mg/l 10.3 total hardness 7.) dH 11.1 Total hardness 7) mmol/l CaCO3 1,99 Carbonate hardness °dH 8.5 ...
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Alternatives to EDTA for calcium ion chelation

Are there any $\ce{Ca^2+}$ chelating agents (other than EDTA) that are as good as EDTA in terms of binding calcium ions and effective in a pH range of $5$ to $9$?
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Relationship of CO2 in water

We have an evaporative cooling system here at the power plant that uses city water. The water is pumped up and cascades down across a filter media cooling the intake air to the gas turbine. This is ...
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How fast does atmospheric carbon dioxide dissolve into strongly basic solution?

I'm conducting some pH measurements with solutions containing NaOH and I'm a bit concerned that carbon dioxide will dissolve and affect my measurements by lowering the pH according to the reaction: $$\...
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Potassium phosphate buffer + EDTA

Given 10 mM potassium phosphate buffer (pH = 7.0), 50 mM potassium propionate and 20 mM EDTA (acid). After addition of all 3 components pH becomes 4 since EDTA has 4 $\ce{OH}$ groups. How to ...
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Why is it difficult to measure the pH of environmental water samples accurately (near 7)?

I've read in several places (edit: 1, 2, 3, 4, 5, 6, 7, 8. 9, 10, 11, 12) that there are many practical factors that make accurate pH measurements of roughly neutral environmental water samples more ...
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How to slow/prevent corrosion of a steel post

I have a steel post set in limestone, about 18-20 inches deep, with some concrete around it. I just noticed that I have about 6 inches of water inside the post. The limestone had a small seam in it ...
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How does increasing ionic strength affect the pH of solution?

I'm having trouble interpreting the data for an experiment. With increasing ionic strength, I found lower solubility but also lower pH of the solution. What is the effect of the ionic strength on the ...
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Does water acidity affect sugar solubility?

For example, when making lemonade: will mixing sugar in water after adding lemon juice lead to a slower sugar dissolving rate, than if sugar were mixed in before adding lemon juice?
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pH and solute solubility in waste mixed water

I was reading a module on waste management. There were two interesting points. High pH results in higher solubility of $\ce{CN-}$. I understand that for HCN: $$\ce{HCN ->H+ + CN-}$$ Higher pH ...
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pH, conc vs activity

After studying a somewhat overview of "gamma" activity coefficient (it is not actually in our course but may come in exam as a part of unknown paragraph in ionic equilibrium) I can understand most ...
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How to calculate concentrations when dissolving two salts?

Some solid silver bromate was dissolved together with solid silver acetate what would be the highest achievable pH? \begin{align} K_\mathrm{sp}(\ce{AgBrO3}) &= 5.38 \times 10^{-5}\\ K_\mathrm{sp}...
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Buffer capacity of different types of milk

Currently I am tasked with designing an experiment that that I will have to perform in 2-4 weeks, but I don't have to decide on on a topic soon. I was thinking of performing an acidometric titration (...
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pH meter and paraformaldehyde

We have had an ongoing debate in our lab and several bad pH electrodes. I would like to ask the following question Do paraformaldehyde soloutions (2-4% w/v) damage pH meter electrodes? If so, why?
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Isoelectric point pH, mV, for a metal oxide nanopowder

I'm trying to make a solution of $\ce{TiO2}$ that will coat stuff in as dense a monolayer as possible. To do so, I'm using nano sized $\ce{TiO}$ particles and trying to get them to get as close to ...
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Understanding how the definitions of pH and activity are compatible

At $T=\pu{25 ^\circ C}$ and $P=\pu{1bar}$, the density of water is $\pu{0.997 kg L-1}$. Neglecting nonideality of the mixture $\ce{H2O(l), H+}$ and $\ce{OH-}$ (all activity coefficients are close to $...
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Calculating the pH of a weak acid from the Kb of its conjugate base

I'd start off by saying it's been many years since I was in chemistry lessons and have forgotten much, but recently I have had to relearn a lot of basic chemistry. The following doesn't really impede ...
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Does negative pH mean it is a stronger acid than one with positive pH?

I've searched this site but I don't think this has been asked yet. Does negative pH indicate a stronger acid than a positive pH (since it's further down the scale)? I'm asking this because in one of ...
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Is endpoint pH concentration dependent? Choosing an acid/base indicator

We use titrations to determine analyte concentrations with a standardized titrant and an acid/base indicator, BUT how do we choose the indicator? It is my understanding that indicators are supposed to ...
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Henderson-Hasselbalch approximation

The Henderson-Hasselbalch approximation gives us a method to approximate the pH of a buffer solution. The basic equation is as follows: $$\mathrm{pH} \approx \mathrm{p}K_\mathrm{a} + \log\dfrac{\ce{[...
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Why does [H3O+] of a buffer change very slightly when diluted?

I am confused as to why the [H3O+] of a buffer changes very slightly when diluted (at least in an intuitive sense). Consider: $\ce{HNO2 + H2O <=> H3O+ + NO2-}$ [$\ce{HNO2}$] = 0.45 M and [$\...
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pH at different concentrations

In making gummies with pectin, the pH is very important and needs to be at or below 3.4. USP indicates dissolving it in a 10% solution to test the pH, while some use a 50% solution. I'm told the ...
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Can buffers regulate the pH, or do they just smooth out pH bumps?

Hydrogen carbonate can react with hydrogen ions to create carbonic acid which degrades into water and carbon dioxide that can be exhaled or excreted otherwise. That lowers the pH, yes. However, in ...
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Determining pH of immunoprecipitation buffer recipe

I'm following a protocol for extraction of proteins from yeast, and I came across this recipe for immunoprecipitation buffer: $\pu{50 mM}$ HEPES-$\ce{KOH}$, pH 6.8, $\pu{150 mM}$ $\ce{KOAc}$, $\pu{...
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Determining the acid dissociation constant change with temperature in sparkling water

I already have the different values of pH at the different temperatures, but what I'm trying to figure out is obtaining the acid dissociation constant using these pH values. Is there a way I can do ...
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Wondering how I should have graded this question (freshman lab, about buffer capacity)

I TA the intro freshman lab course. In a lab about buffers and buffer capacity, the students were instructed to make 50 mL of a 0.1 total molar pH 6.70 buffer by dissolving solid $ KH_2PO_4 $ and $ ...
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What is the pH of a solution that results of a mixture of two others with known pH?

Solution A has a pH of 1, soultion B has a pH of 6. If I mix the same volume V of each solution into one, what will be the pH of the resulting solution? I'm guessing here as no more information has ...
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How to calculate the gas-liquid interaction for dissolved HNO3 in water with air?

Thanks for reading this and (maybe) helping me in advance! I have to face the following problem: I have got $\ce{HNO3}$ dissolved in water (roughly $\pu{50\%}$) and I want to know how much $\ce{HNO3}...
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How can you perform an acid-base titration with antacids if substances, like aluminium hydroxide, are insoluble?

I am trying to perform an experiment in order to determine the efficiency of different antacids. An online search later shows that you add an HCl solution in a solution created with a base/antacid. ...
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pH notation in text

When referring to units of pH in continuous text (i.e. not in a table), which is the recommended usage? pH 7 to pH 8 pH 7 to 8 What about when the term "pH" has already been mentioned in the text? ...
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Calculating the pH of buffer solution made of two salts of a polyprotic acid

When we are making a buffer solution by solutions of a weak acid and its salt like $\ce{CH3COOH}$ and $\ce{CH3COONa}$, or by a weak base and its salt like $\ce{NH3}$ and $\ce{NH4Cl}$, we can use the ...
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How to find pH of an aqueous ammonia solution at high pressures?

Here's the simplified question: I start with $15~\%$ of $\ce{NH_3}$ and I want to find the $\mathrm{pH}$ of the following reaction at $25~\mathrm{^\circ C}$ and $5\ \mathrm{kbar}$: $$\ce{NH_3 + H_2O -&...
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The potential range of the cyclic voltammetry of CoCat in KPi made of D2O

I have a phosphate buffer adjusted to pH 7, and another phosphate buffer made of deuterium oxide (D2O) adjusted to pH 6.6 (pD 7). I want to conduct cyclic voltammetry of cobalt oxide catalyst in these ...
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Derivation of buffer capacity

I read an article about Buffer capacity The reaction is: $\ce{HA <=> H+ + A-}$ They have given that: But shouldn't $C_{buf}=[HA]+[A^-]+[H^+]$ ? The total concentration at equilibrium is $c(...
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Is the pH of a solution (orange juice) affected by the presence of a metal?

Is the pH of a solution (orange juice) affected by the presence of a metal (aluminium, tin or iron for example)? I know that the metal will corrode in the presence of an acid (citric acid in this case)...
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Find H3O+ of weak acid salt solution which compose of solute that can gain and give protons

Find $[\ce{H3O+}]$ of 0.100 M $\ce{NaHCO3}$ ($K_{\ce{H2CO3},1}=4.45×10^{-7}$, $K_{\ce{H2CO3},2}=4.7×10^{-11}$) My work is: $$\ce{HCO3- + H2O<=>H2CO3 + OH-}$$ Initial: $[\ce{HCO3-}]$ = 0.100 M, ...
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Deviation from ideal solutions - activities and concentrations

What are some examples of solutions deviating significantly from ideal behavior, and, by extension, showing pHs significantly different from those predicted by usage of concentrations instead of ...
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Calculation of partial charges and protonation/deprotonation states depending on pH

What is the best method for calculating partial charges and protonation/deprotonation states of a small molecule such as phenol or caffeine, depending on the pH? For instance, it is well known that ...
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Preparation of Copper (II) Sulfate Pentahydrate Solution

how would you make a solution of Copper (II) Sulfate Pentahydrate to achieve 150, 200, 250 and 300 mgL−1 concentration of copper? I do not have the anhydrous version of the solute. Also, when I ...
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Is it possible to determine the pH that results in maximum buffer capacity from a Bjerrum plot?

If buffer capacity is normally at a maximum when pH=pKa because there is an equal concentration of acid and conjugate base in the buffer (so there's an equal amount of substance that can absorb acid ...