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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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 ...
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Buffer Capacity Calculation

I know buffer capacity is the following: $$β=\frac{Δ(\ce{H+})}{Δ(\mathrm{pH})}$$ specifically the amount of acid/base that needs to be added to change pH by 1 unit. If I have data about how pH of a ...
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Calculating Buffer Capacity

I completed a titration of Ammonium Acetate buffer solution and to it I added $\pu{2M}$ Hydrochloric Acid. I measured the initial $\ce{pH}$ of the buffer solution before any acid was added and I ...
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59 views

Why does buffer capacity of tartrate buffer generally decrease as the buffer pH increases?

From what I see, the buffer capacity of tartrate buffer is generally decreasing as buffer pH increases. Why is this? Also, does this mean that tartrate buffer doesn't have a maximum buffer capacity at ...
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Effects of Ka on the Half-Equivalence Point

I'm new to studying chemistry at a university level and am currently reviewing acid-base titrations. I am wondering about the relationship between your ionization constant for a weak acid ($K_\mathrm{...
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Dissociation degree hell, Ostwald's law of dilution

Greetings dear chemists! I got a nice exam problem on wich i am stuck for hours, well maybe the problem is with me. I know the problem can be solved. So here we go. We got a weak monoprotic acid, we ...
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Drug pH and pKa known, is it an acid or a base? [closed]

I want to answer the question if a drug which is analysed for pH and pKa is ionised or not ionised in a cow stomach with a pH of 6. The drug has a pH of 8,52 and a pKa of 8,78. Since the pH is 8,52 ...
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480 views

How to make a pH 6.8 Tris buffer?

To preface this, I am a biologist. I need to make a $\mathrm{pH}=6.8$, $\pu{1 M}$ Tris buffer. We have access to Tris base and Tris Hydrochloride. (Unfortunately, none of the fancy Tris compounds ...
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The pH scale/calculating pH level [closed]

How much water do you need to add to 10 mL of a solution of HCl with a pH of 4 to change the pH to 5?
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628 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} ...
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Identifying Lewis acid

What is the Lewis acid on the reactants side? $$\ce{HNO2(aq) + HPO4^{2-}(aq) <=> NO2-(aq) + H2PO4-(aq)}$$ The book says it is the $\ce{H+}$ only, not the whole molecule of the nitrous acid, ...
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not understanding buffering region vs equivalence point [closed]

"During the titration of a weak polyprotic acid with a strong base, the first stoichiometric equivalence point occurs when the moles of added base are equal to the moles of the initial acid species. ...
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Can hydrofluoric acid etch glass at a pH of 7.0?

Will it still etch glass when very dilute? Will the reaction still proceed slowly? At what pH will the reaction stop completely? From Wikipedia on hydrogen fluoride: "Although hydrofluoric acid is ...
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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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Identifying unknown solution with indicators. why is one pKa value ignored and how to treat negatives values?

Three test tubes contain an identical solution of unknown pH. The first one is tested with thymolphthalein and turns colourless The second is tested with a-naphtholphthalein and turns blue ...
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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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Determination of pKb of a mono acidic base

$20$ mL of a weak monoacidic base($\text{BOH}$) requires $12$ mL of $0.3$ M $\text{HCl}$ solution for the equivalence point. During titration, the pH of the base solution was $10$ upon the addition of ...
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How to calculate pH of solution made of H3PO4 and Na3PO4? [closed]

I am unable to calculate the $\mathrm{pH}$ of a solution made of $\pu{0.1 M}$ $\ce{H3PO4}$ and $\pu{0.05 M}$ $\ce{Na3PO4}$. How to set the approximation and which ions are present at the ...
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NMR Prediction for compounds at variable pH values

Like the title says, I'm looking for any software package that may be able to simulate a variety of NMR at a variety of different pHs. The majority of the software programs that I've found do not have ...
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843 views

Why proton concentration is divided by 10⁻⁷?

I am reviewing the book Biochemistry Concepts and Connections by Appling, Cahill, and Mathews and I cannot understand why they divide by the hydrogen concentration by $10^{-7}$. Why not just leave 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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25k views

How do I calculate how much sodium hydroxide I need to add to get a new pH?

A 100 ml $\ce{HCl}$ solution has a pH of $3.7$. You want the solution to be of pH 4.5. You have a solution of $10\ \mathrm M$ $\ce{NaOH}$. How much $\ce{NaOH}$ do you need to add to to the $100\ \...
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Should the tip of the burette of an automatic titrator be immersed in the analyte?

In all the tutorials I found online, the tip of the burette (containing the titrant - NaOH) was immersed into the analyte solution. My question is: shouldn't the tip be out of the solution? Isn't ...
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What are the concentration changes when diluting an equimolar acetic acid: acetate buffer?

When a buffer (for example, a mixture of 100 mM acetic acid and 100 mM acetate), is diluted 10-fold, all the concentrations change drastically. Surprisingly, after re-establishment of equilibrium, the ...
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How is preparing a buffer possible?

I understand the concept of an equilibrium buffer solution, however I am a bit hung on how creating it doesn't shift the weak acid equilibrium. $$\ce{CH3COOH + H2O <=> CH3COO- + H3O+}$$ $$ K_\...
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How do indicators work when they mixed with each other?

Methyl orange, bromothymol blue and phenolphthalein indicators were mixed together to form a solution. Over what pH range would the solution be yellow? I cannot understand the question. If two or ...
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523 views

The effect of NaCl on the ability of an acid to protonate benzoate

I've been doing several experiments using soda to quantify the amounts of caffeine and benzoate. Because of our methods of analysis, we had to decarbonate our soda. The experiment offered two ways for ...
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1k views

net charge nucleobases at alkaline conditions

While doing anion exchange chromatography of a short oligonucleotide, I have noticed that at $\rm pH=12$, the oligo retains longer on the column than the same oligo- at $\rm pH=8$. I thought the ...
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394 views

What alkali and alkaline earth metal oxides will turn moist red litmus blue and finally white? [closed]

How many of the following will turn moist red litmus blue and finally white? $\ce{Li2O}$, $\ce{KO3}$, $\ce{RbO2}$, $\ce{Cs2O2}$, $\ce{BeO}$, $\ce{MgO}$, $\ce{BaO2}$, $\ce{SrO}$. Since bleach ...
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What is the benefit of using a pH indicator reagent over pH strips or a meter?

I've recently started getting into chemistry a bit as a hobby. Nothing serious, just amateur level stuff mostly, primarily just to educate myself. Whenever I need to determine the pH level of a ...
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Dissociation behaviour of polyelectrolytes

Assuming a solution of 100 polycationic molecules, each of them carrying 100 amino groups and an apparent pKa of 6.5. Would it mean that, at a pH of 6.5, 50 molecules will be fully protonated 50 ...
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130 views

Can an acid have a high pH? [closed]

I am studying anesthetics and came across thiopental which is considered a weak acid. However it has a pH of 10.5. I always learned that greater than 7 is alkaline. I’m looking for some guru to help ...
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How is seawater alkaline?

If when water and carbon dioxide react they form carbonic acid, carbonate, and bicarbonate, how does seawater still have a pH of around 8? Doesn't a compound need an hydroxide ion to be a base?
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Concentration of Hydrogen Ions

I am slightly confused about one certain task. There are 4 different solutions ($\ce{NH3}$, $\ce{HCl}$, $\ce{NaOH}$, $\ce{CH3COOH}$), their concentration is the same $(c = \pu{1 mol L-1}).$ Which ...
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Solubility and pH

I was reading about antacids. It stated that in earlier times $\ce{NaHCO3}$ and a mixture of aluminium and magnesium hydroxide were used as antacids. In excess $\ce{NaHCO3}$ can make the medium ...
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Acidic and alkaline salt solutions: why do some salt form acid/bases while others don't

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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Calculating dissociation degree from pH and Ka without given initial acid concentration

Is it possible to calculate the dissociation degree (DD) from pH and Ka without directly been given the initial acid concentration? I found the following formula: $$\text{DD} = \frac{K_\mathrm{a}}{...
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838 views

Calculating the pH of a ammonium hydrogen sulfate solution

I am attempting to complete a question in which I need to use an ICE table to calculate the pH of a $\pu{2.61 mol L-1}$ $\ce{NH4HSO4}$ (ammonium hydrogen sulfate) solution. When $\ce{NH4HSO4}$ ...
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How to calculate the pH of a solution given the concentration and pKa's of solutes? [closed]

For example, if I have a solution of 50mM acetlycholine (pKa = 4.5), how would I go about calculating the pH of the solution? Thanks
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539 views

What is the pKa of iodous acid?

Searching the web readily gives the $\mathrm{p}K_\mathrm{a}$ of hydroiodic acid, hypoiodous acid, and iodic acid, however, extensive searching did not result in any value of the $\mathrm{p}K_\mathrm{a}...
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pH change with temperature

I understand that the pH of solutions decreases as the temperature increases but is there a reason as to why some solution's pH decreases more than others even if the temperature change is the same?
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Determining the pH of an organic solvent

Our work is faced with the issue of determining the charge of compounds that are dissolved in chloroform. One could realistically determine the charge of the relevant moieties knowing the $\mathrm{p}...
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Evaluate mass of salt needed to add to a buffer solution knowing only pH

This is an exercise taken from an old exam, I'm struggling with the resolution. To a solution of a generic weak acid $\ce{HA}$ were added $\pu{2.40 g}$ of a potassium salt of the $\ce{KA}$. The ...
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What could be causing noisy pH measurements?

I designed and built a hydroponics system with pH logging and I am trying to understand why pH measurements in the nutrient reservoir vary ~ ±0.2 pH while measurements in a separate bottle of probe ...
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Volume required to dilute solution for a pH change

A $\pu{100 mL}$ solution of $\ce{NaOH}$ has a $\mathrm{pH}$ of $13$. What volume of water in $\pu{mL}$ must be added to change the $\mathrm{pH}$ to $11$? My steps: Begin by calculating conc. of $[\...
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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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Why will a strong acid neutralize as much base as a weak acid?

This is a simple concept that I can't seem to understand. Why will a strong acid neutralize as much base as a weak acid, if the acids are of the same volume and concentration? A strong acid will ...
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649 views

Why can't the strength of superacids be measured in water?

I learned about acid strength, that the strength of an acid increases with it's degree of ionization when solvated. So, in water, a strong acid is one where $\ce{[H_3O^+]}$ is large, which is equal to ...
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Why must a buffer solution contain both a weak acid and a salt solution of its conjugate base?

Doesn’t the weak acid dissociate to produce the conjugate base on its own? I understand that when a strong base is added to the buffer solution, the hydroxide ions will react with the hydrogen ions ...
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Does the number of H+ ions in solution go up on dilution of a weak acid?

In my textbook, a footnote says: In case of weak acids, on dilution the total number of $\ce{H^{+}}$ ions in solution increases because dissociation of the weak acid increases This didn't make ...