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Questions tagged [acid-base]

This tag should be applied to questions concerning acid and base reactions. An acid is capable of donating a hydron/ proton (Brønsted acid) or capable of forming a covalent bond with an electron pair (Lewis acid). A base on the other hand is a chemical species/ molecular entity having an available pair of electrons capable of forming a covalent bond with a hydron/ proton (Brønsted base) or with the vacant orbital of some other species (Lewis base).

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3answers
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Comparing basicity of imidazole and 2-imidazoline

I recently sat for an exam in which I was asked to compare the basicity of the above compounds. I thought imidazole would be more basic because it is aromatic but according to the answer key 2-...
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What bases are fit for human consumption and can be used in foods?

I know that are several acids that can be found in the kitchen, such as citric acid and vinegar. However, I never heard of a base that can be used in the kitchen to raise the pH levels of any food. ...
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pKa values for protonated nitrogens in ketoconazole

Everywhere on the internet I see that the two $\mathrm pK_\mathrm a$'s of ketoconazole are 6.4 and 2.3, but I don't think that is correct. The $\mathrm pK_\mathrm a$ of imidazole is around 6.4 . ...
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Is the Henderson–Hasselbalch equation volume independent?

Looking at this equation $\mathrm{pH} = \mathrm{p}K_\text{a} +\log\frac{[\ce{CB}]}{[\ce{A}]}$ makes me think that it is concentration independent. What I mean is, when we look at $\frac{[\ce{CB}]}{[\...
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Can I make a buffer from two different weak acids or bases?

Can I make a buffer using two different acids/bases? For example, adding 1 mole of acetic acid and 1 mole of ammonia? The only information I can ever find is that I can make a buffer using only an ...
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1answer
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To add acid or base to water

There is a rule stating that we shall add a strong acid to water, and not the other way because of safety; if we would add water to the acid, the reaction could be dangerous (boil). What about adding ...
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Will cinnamaldehyde undergo self-aldol condensation?

Will cinnamaldehyde undergo self-aldol condensation? My book says it won't, but since it has an α-hydrogen, I'm confused.
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Do enolates get protonated at the carbon or oxygen atom?

An enolate has two resonance structures. When it gets protonated, where is the $\ce{H+}$ more likely to go? On the oxygen to produce an enol, which tautomerizes to the keto, or on directly onto the ...
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Why is glycine hydrochloride more acidic than chloroacetic acid?

I cannot figure out why glycine hydrochloride is more acidic than chloroacetic acid. Could I have figured this out from a $\mathrm pK_\mathrm a$ table and maybe am just not seeing it? On the table I ...
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1answer
320 views

How can I determine the pH of solution?

Could anyone tell me how I would go about calculating the pH of 100.0 mL of 0.100 M $\ce{H2NNH2}$ ($K_\text{b} = 3.0 \times 10^{-6}$). Furthermore, how would this pH change when 20.0 mL of 0.200 M $\...
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Is steric inhibition of resonance or steric inhibition of protonation dominant in o-toluidine?

I wish to know which effect out of steric inhibition of resonance (SIR) or steric inhibition of protonation (SIP) is dominant over the other when comparing basicities of o-toluidine and aniline: ...
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1answer
163 views

Why don't Gringard Reagents react with carbonyls at the alpha position? [duplicate]

According to many texts, the reason why Gringard reagents cannot be used with alcohols is because the Gringard reagent is a strong base, which would deprotonate the alcohol. ($p\pu{K}_b$ of Gringard $\...
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Is the conjugate base of pyrrole resonance stabilised?

This is something I am conceptually struggling with, if I deprotonate pyrrole on the nitrogen in the ring, is it true that the conjugate base is not resonance stabilised, because the orbital is ...
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1answer
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Does dilution of a buffer affect pH?

The Henderson-Hasselbalch equation for the $\mathrm{pH}$ of a buffer solution of the monoprotic acid $\ce{HA}$ is given by $$\mathrm{pH}=\mathrm pK_\mathrm a+\log{\frac{[\ce{A-}]}{[\ce{HA}]}}$$ Since ...
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1answer
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Comparing the Lewis acidity of carbon tetrafluoride and silicon tetrafluoride

I've been asked to compare the relative acidity of $\ce{CF4}$ and $\ce{SiF4}$. As both atoms have noble gas configurations, neither can act as a lewis acid and so I assume the question is inferring ...
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Is there a difference in the reactions of a dilute acid and a concentrated acid?

All of the exams that I've sat so far, and the homework questions I've had, always ask for the reaction between a substance and a dilute acid. Is there a difference in the reaction between a dilute ...
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1answer
526 views

Buffer Power of the amphiprotic substance

The mass balance for a generic amphiprotic substance $[\ce{AH^-}]$ this: $$ [\ce{HA^-}]=C \cdot \dfrac{K_{a1} [\ce{H_3O^+}]}{K_{a1}\cdot [\ce{H_3O^+}] + [\ce{H_3O^+}]^2 + K_{a1} \cdot K_{a2}} \quad ...
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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 $\ce{CH_3COOH}$ ...
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246 views

How to derive the conductivity titration curve which accounts for salt formation

I derived an equation that gave me the volume of base required to get a certain $\mathrm{pH}$: In a titration between a weak acid $\ce{HA}$ and weak base $\ce{B}$ (adding base into acid solution) the ...
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Calculating pKa's using Gaussian

I've been learning to use Gaussian recently and I found a question here that seemed like a good opportunity for me to practice. I know that I can obtain $K_a$ from $$\Delta G=-RT\ln(K_a)$$ using the ...
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Which will be the most acidic hydrogen in the following organic compounds?

Which will be the most acidic hydrogen in both cases? Please explain. According to me, in the first compound 2 should be most acidic as in both 1 and 2, resonance occurs but 2’s carbon is closer to ...
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How does sodium bicarbonate act as a deodorizing agent?

I was reading this other question on the site: Deodorizing using baking powder instead of baking soda. Apparently, baking soda is used quite often as a cleaning and deodorizing agent. From what I ...
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Formation of zwitterion from amino acids

Why it is easier for the carbonyl group to lose a proton to become negatively charged and the amino group to accept a proton to become positively charged? I know it has to do with the very polar bond ...
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1answer
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Sodium carbonate titration in presence of phenolphthalein

Why phenolphthalein cannot show the endpoint for the complete titration of Na2CO3 with only phenolphthalein? What's the reason that we consider only half of the moles of sodium carbonate when ...
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1answer
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Mechanism for acid-catalyzed dehydration of 2,3-dimethylcyclopentanol

How do you get from 2,3-dimethylcyclopentanol to 1,2-dimethylcyclopent-1-ene? I know the -OH group leaves as water (being protonated by acid) forming a carbocation. Then the weak nucleophile (water) ...
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Carbon and dilute sulfuric acid

I have to distinguish between copper oxide and carbon. I thought of dilute sulfuric acid because it forms copper sulfate with copper oxide. But I don't know how carbon reacts with dilute sulfuric acid....
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1answer
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Adjusting PBS with HCl: pH drift after dilution of phosphate buffer

It is some kind of everyday lab science and with a feel of shame I cannot answer this observation. I noticed a pH drift (~0.5 units) of my 10X phosphate buffer (PBS), when I adjust the pH with $\ce{...
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If the pH is zero, what would be the normality of a sulphuric acid solution?

If pH of the solution is zero, what would be the normality of $250 \, \mathrm{ml}$ $\ce{H2SO4}$ solution? My work: $\mathrm{pH} = 0$, hence the concentration of $\ce{H+}$ ions is $\pu{1 mol L^-1}$, ...
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Selective etchant for Al2O3 (Does not etch Al, Cu, Zn, Sn)

I'm looking for a wet-etchant to remove aluminum oxide created by anodizing, but not etch the unoxidized metal (with greater than 10:1 selectivity) I know about chromium(IV) oxide and fluorine-based ...
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1answer
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Colour change of fluorescein in acidic and basic medium

I prepared fluorescein for my chemistry project in school and I realised that this molecule and its preparation steps are very closely related to that of phenolphthalein. I have studied briefly about ...
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How to calculate the pH of a 0.325 M solution of pyridine hydrofloride?

How to calculate the $\mathrm{pH}$ of a $0.325~\mathrm{M}$ solution of $\ce{C5H5NHF}$? The $K_\mathrm{b}$ for $\ce{C5H5N}$ and $\ce{C5H5NH+}$ is $1.7\times 10^{-9}$. Here's my work, but it's wrong (...
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Exceptionally weak basicity of pyridine [duplicate]

It is often explained that the relatively lower basicity of pyridine, relative to most amines, is due to the fact that the $\ce {N}$ lone pair resides in an $\ce {sp^2}$ hybridised orbital, instead of ...
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461 views

Does phosphoric acid remove stainless steel electropolished layer?

Electropolished stainless steel has a high corrosion resistance due to the oxide film that is created during electropolishing. The film mainly consist of chromium(III) oxide. Phosphoric acid is ...
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Why does potassium react the most vigorously with water?

Link to exam Which metal reacts most vigorously with water? (A) Ca (B) K (C) Mg (D) Na The given answer is B and the reasoning is that is is the most electropositive since it the furthest ...
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5answers
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How to calculate the concentration H3O+ in a solution with pH=6.99?

What is the correct way to calculate the concentration $\ce{H3O+}$ in a solution with $\ce{pH}=6.99$? Attempt 1. pH<7, therefore there are only $\ce{H3O+}$ particles in the solution. $[\ce{H3O+...
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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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Does H3O+ donate a H+ to Water?

Does the hydronium ion donate a proton to water? If the collision of 2 molecules of water can cause a proton to be transferred, does hydronium 'pass' a proton to water?
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Which definition of Acids and Bases conforms to the pH scale?

It's all in the title. Is it the Arrhenius or the Brønsted-Lowry definition? Or is it some other definition? Also, our teacher told us that $pH$ stands for "Power of Hydrogen", but some sources say ...
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Adding lemon to lentils changes color from black to pink, why?

I noticed that when I cook black lentils and add lemon juice to the water that's left, the water turns from black to pink! What can be the reason for that?
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Why can't alcohols turn blue litmus red?

I came across the fact that alcohols cannot turn blue litmus red. The fact confuses me as they are acidic and acids do turn blue litmus solution red. What prevents alcohols from turning blue litmus ...
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Alkalis and Bases

I just learnt about acids and bases at class.I noticed that my textbook mentions the term "alkali/alkaline" and sometimes it mentions "base/basic". As far as I know, alkalis and bases are metal oxides ...
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How to identify a redox reaction?

Which balanced equation represents a redox reaction? \begin{align} &\mathrm{A.} &\ce{AgNO3 + NaCl &-> AgCl + NaNO3} \\ &\mathrm{B.} &\ce{BaCl2 + K2CO3 &-> BaCO3 + 2KCl} ...
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Why does the hydroxide ion have a negative charge?

I've been studying the roles of hydroxide & hydronium in acids and bases, and it was mentioned that a hydroxide ion (OH-) has a negative charge. Can someone give me a layman's explanation of what ...
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443 views

Can hydroxides ionize alcohols?

For example, can $\ce{NaOH}$ ionize ethanol into ethoxide? My textbook (Organic Chemistry, 6th edition, by M. Loudon and J. Parise, Roberts & Company 2016) suggests yes — it uses it in its ...
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1answer
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Why, in titration, is universal indicator not commonly used?

My teacher said that we always used indicators such as methyl red, methyl orange, litmus, phenolphthalein, etc. rather than universal indicator. I don't understand why, though, would not universal ...
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3answers
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Is magnesium sulfate basic, neutral or acidic?

A question in my college test was whether $\ce{MgSO4}$ is neutral, acidic or basic. I was told to solve this kind of problem by hydrolyzing any ions that do not "come from" a strong acid or a strong ...
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1answer
481 views

Why is dimethyloxonium cation stronger acid than hydronium?

$\ce{(CH_3)_2O^+ H}$ has $\rm pK_a \; -3.8$ while $\ce{H_3O^+}$ has $\rm pK_a \; 1.74\;.$ So, the former is stronger acid than latter hydronium ion. But why is it so? Is it due to the $\rm +I$-...
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How to rationalise that when we dilute a weak acid, the pH increases but also the dissociation increases?

When water is added to a weak acid like ethanoic acid, the number of ethanoic acid molecules that dissociate increases, however, pH increases (less acidic), too. Why is this so?
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1answer
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Pipetting strong acid with plastic material

Can I pipette concentrated sulfuric acid using a plastic pipette tip? Will either the plastic or the acid be affected?
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Comparison of acids to dissolve phosphates

I am currently reading this German paper on the dissolution of phosphates by acids and chelants. The authors do a "fast-test" of the dissolving power of different acids which goes as follows: For ...