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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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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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Hydrolysis of salts containing amphiprotic anion

I am trying to understand the derivation of pH of salt containing amphiprotic anions, but I am facing some difficulty: Ionisation: $\ce{HCO3^- + H2O <=> CO3^2- + H3O+};\quad K_\mathrm{a_2}...
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How much NaOH required to change the pH of a weak acid solution by 2

If I have a $\pu{20mL}$ $\pu{0.1M}$ solution of sodium dihydrogenphosphate, how much $\pu{0.1M}$ $\ce{NaOH}$ do I need to add to raise the $pH$ by 2. Here's what I've done so far. I'm doubt it's ...
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What is the Iso electric point of the given amino acid? [closed]

I am not sure about three but for two acidic parts we take the mean of the two.. But what about three?
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222 views

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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Is there a pH at which all proteins are negatively charged? How can it be determined?

I know that depending on the amino-acid-composition of the peptide the distance to the isoelectric point determines the charge. Is there a universal point at which all proteins are definitely ...
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pH of aqueous solution of HCl of low concentration [duplicate]

What is the pH of $10^{-8}~\mathrm{M}$ $\ce{HCl}$ solution in water? My attempt: pH = $-\log(10)^{-8}$ = 8 But this is wrong because it should be acidic. Where have I gone wrong?
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Simple experiment to do at home that involves acids and bases? [closed]

so long story short I am in the IB Diploma and I am required to come up with an experiment to investigate pretty much anything to do with chemistry. I'm thinking about doing mine on investigating how ...
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1answer
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Is following graph is of a dibasic or monobasic acid?

Is the above graph is of a dibasic or monobasic acid? There is slight hint of it being of dibasic around 15. But is it enough to conclude ? I am confused.
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Does gold always become gold chloride when dissolved with HCl and an oxidizer and can it always be precipitated with sodium metabisulfate?

I tried to extract gold from computer parts by STRIPPING the gold using $\ce{HCl}$ and $\ce{H2O2}$ by dissolving the copper & nickel underneath but i added FAR too much $\ce{H2O2}$ by a stupid ...
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520 views

Does higher [OH] not entail higher pH?

A student has equal volumes of $\pu{1.0 mol dm-3}$ sodium hydroxide and ammonia solutions. Which statement about the solutions is correct? A. Sodium hydroxide has a lower electrical conductivity ...
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Finding pH using the mass of an acid, Kw and the volume that is produced

I'm curious about how one would go about this. As an example: 9 grams acetic acid ($\ce{CH3COOH}$), mixed with enough water to produce an 800 mL solution. Find the pH. My progress: $$\frac{\ce{8.7 ...
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Calculating the pH of a mixture of Na2HPO4 and Na3PO4?

I know there are more questions about this on the forum, but I was just wondering: when we mix both solutions, would we have to consider the equilibria corresponding to $\mathrm{p}K_\mathrm{a2}$ and $\...
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1answer
152 views

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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1answer
108 views

Buffers: what does the strong base react with?

I am a bit confused on buffers: If I have a solution with a weak acid (say $\ce{NH4}$) and its conjugate weak base ($\ce{NH3}$), I have a buffer solution (in $\ce{H2O}$). $$\ce{NH4 <--> NH3 + ...
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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 ...
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1answer
791 views

Why is finding [H+] when given [OH-]= 3.57e-5 M wrong when I use -log[OH-]?

Question/Problem I know that [H+][OH-]=$10^{-14}$ And the problem asks to find out the concentration of H+ when the concentration of OH- is $3.57*10^{-5}$M By using the equation above i find that ...
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1answer
428 views

How do we know the concentration of hydroxide ions in this derivation?

In the derivation of the pH of a solution of a salt prepared from a weak acid and strong base, I used two equilibrium reactions: $$\ce{ CH3COOH(aq) + H2O(l) <=> H3O+(aq) + CH3COO-(aq)} \qquad ...
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1answer
146 views

pH Curve in Acid/Base Titrations

So I came across a question on the equation of the pH curve, and I wanted to know how the user here arrived at the matter balance equation. Any help would be appreciated! Here is the question: The ...
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1answer
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Does the solubility of iron (iii) oxide increase when the pH of the water it is in decreases? [duplicate]

I did an experiment and I got these results: pH 4: 3.46 pH 3: 3.77 pH 2: 2.18 pH 1: 3.69 The numbers on the right is the amount of iron oxide remaining that was not filtered. Do these numbers ...
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Why do we use phenolphthalein as an acid-base indicator?

It seems that no resource I come across addresses the fact that the pH range for phenolphthalein's color change is around 8.2-10. In other words, it's still colorless at 8.2. Why then, is it claimed ...
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1answer
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Measuring pH of pasty solutions/mixtures

I'm trying to measure the pH of a very viscous paste mixture and have been told to dilute the sample for more accurate results, because the viscosity of the sample may prevent the sensor to detect the ...
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1answer
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pH Testing Without Cabbage/Disposal of Ferric Chloride

I have a year old bottle of ferric chloride in my basement for PCB etching that I realized that I was never going to use. What is the best way to make sure that it is neutralized without pH paper or ...
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Is the equation pH + pOH = 14 valid at different temperatures?

$\mathrm{pH} + \mathrm{pOH} = 14$ For water at 60 degrees Celsius, $K_\mathrm{w} = 1 \times 10^{-13} = [\ce{H+}] \times [\ce{OH-}]$ Hence, $[\ce{H+}] = 1 \times 10^{-6.5} = [\ce{OH-}]$ So $\...
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Identifying unknown solution with indicators : why is one pKa ignored & how to treat negatives?

3 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 What colour ...
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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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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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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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3answers
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Acid disassociation constant of an acid when pH of a solution is given

Q. A solution contains $\pu{0.09M}~\ce{HCl}, \pu{0.09M}~\ce{CHCl2COOH}$ and $\pu{0.1M}~\ce{CH3COOH}$. The pH of the solution is 1. If $\ce{K_a}$ for acetic acid is $10^{-5}$, then calculate $\ce{K_a}$ ...
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1answer
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Effect of pH on Dilution of HCl Solution

Q. A solution of $\ce{HCl}$ has a $\mathrm{pH}$ of $5$. If $1\ \mathrm{ml}$ is diluted to one litre of water at $\mathrm{pH}=7$. What is the $\mathrm{pH}$ of the resulting solution. Attempt- $$\...
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1answer
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When does phenolphthalein containing solution change colour? [closed]

We were estimating the amount of dissolved $\ce{CO2}$ in water using the American Public Health Association method. It was a Titrimetric Method using phenolphthalein indicator. Titrant used was $\ce{...
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1answer
743 views

Can the colour change in litmus paper be explained by conjugated systems?

I have been trying to understand the colour change in litmus paper on a more detailed level than "the chemical identity changes, and therefore also physical properties". I have knowledge of the ...
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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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Which Pka to use to calculate Z-/HZ ratio of amino acids (henderson hasselbalch)?

I was wondering which $\mathrm{pK_a}$ 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} +\log\...
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Where on the backbone does a peptide get protonated at low pH?

As a particular example, how does the backbone of a peptide look at $\mathrm{pH}~2$? Where does the backbone get protonated in such an acidic solution? I know that at low $\mathrm{pH}$ the free ...
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2answers
637 views

Significant figures in pH calculations: does pH 0.30 count as 2 or 3 significant figures?

Just say I wanted to give a pH calculation to three significant figures. Eg: the $\mathrm{pH}$ of a $0.500 M$ solution of $\ce{HCl}$ is $-\log(0.5) = 0.3010299957...$ Would 3 s.f. be $0.301$ or $0....
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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 to find the equivalence point on a graph of an acid-base titration curve? [closed]

Here is the data taken from the lab: Acid pH, Vol (cm3)[ (9.67, 4cm3) (9.08, 8cm3) (8.70, 10cm3) (8.06, 12cm3) (7.93, 13cm3) (4.76, 14cm3) (2.45, 15cm3) (2.23, 16cm3) (2.10, 17cm3) (2.01, ...
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3answers
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Why are many chemical relationships logarithmic?

I've noticed that in many relationships in chemistry, one variable is linearly related to the logarithm of another. Why is this the case? For example, I carried out an experiment where the dependent ...
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1answer
54 views

How would you go about solving this pH problem?

What is the $\mathrm{pH}$ of a $0.24\ \mathrm M$ solution of benzylammonium chloride ($\ce{C6H5CH2NH3Cl}$)? $K_\mathrm b$ for benzylamine is $2.2\times10^{-5}$ Your answer must be within $\pm 0.4\ ...
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1answer
124 views

pH of salt composed of the conjugate of strong acid and base

salt like [HA]B dissloves in water (here we don't consider its solubility) : $$\ce{HA <=>[$K_\mathrm a$] A- + H+}$$ and $$\ce{B- + H2O <=>[$K_\mathrm b$] HB + OH-}$$ usually we ...
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Detecting Different Beverages

I'm attempting to design a reusable process to rudimentarily differentiate between different beverages. Right now I'm mainly aiming to pick up on differences between coffee and tea, which is a little ...
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2answers
8k views

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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1answer
2k views

Does NaOH have a higher OH- concentration than NH3?

In my book it's a multiple choice question with only one correct answer. There are two solutions of $\ce{NaOH}$ and $\ce{NH_3}$ that have similar concentrations and volumes. These two are among ...
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1answer
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Why isn't the side chain of arginine totally protonated at low pH?

I was wondering why arginine cannot be protonated at $\mathrm{pH\ 0}$ on all the $\ce{N}$ atoms in the side chain, as they all have a free electron pair. As this image shows, it can only be protonated ...
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2answers
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Why is a buffer solution best when pH = pKa i.e. when A-/HA=1

Buffers work best when $\mathrm{pH}$=$\mathrm{p}K_\mathrm{a}$ From the Henderson-Hasselbalch equation, $\mathrm{pH}= \mathrm{p}K_\mathrm{a} + \log_{10}\left(\frac{[\ce{A-}]}{[\ce{HA}]}\right)$ If $...
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2answers
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Is methyl orange acidic or basic?

It has been saying that if adding too much indicator in solution, the ph value of solution would be changed. From this, it can be saying that indicators have a pH value. Methyl orange is the indicator ...
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How to calculate pH of solution made of H3PO4 and Na3PO4?

I am unable to calculate the pH of a solution made of: $\ce{H3PO4}$ $\ce{0,1 M}$ $\ce{Na3PO4}$ $\ce{0,05 M}$ How to set the approximation and which ions are present at the equilibrium?
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1answer
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Volume expansion from phosphate buffer solution

I want to mix a phosphate buffer at $\mathrm{pH\ 7.2}$ at $20~\mathrm{^\circ C}$. I do this by dissolving $0.0036\ \mathrm{mol}$ of sodium dihydrogen phosphate monohydrate ($\ce{NaH2PO4*H2O}$) and $0....
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1answer
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How do you determine the pH of a solution at different volumes?

For a tube with 1 mL of 0.75 % (w/v) casein in 0.10 M sodium acetate, with 0.05 mL acetic acid, and 6.95 mL H2O, how do you determine the pH? My original thought was to use the Henderson-Hasselbalch ...