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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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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How do I calculate the concentration of sulphuric acid by a titration experiment with sodium hydroxide?

In my latest chem lab the objective was to create a primary standard of $\ce{NaOH}$ and use it to determine the concentration of sulfuric acid. The first part of the lab was determine the molarity of ...
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Why does hydrogen bonding in salicylic acid make it more acidic?

When salicylic acid deprotonates (losing the proton from the carboxyl group) it forms a hydrogen bond with between the oxygen in the carboxylate anion and the hydrogen in the alcohol group. However, ...
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Protonating/basic site and Brønsted basicity orders of beta, gamma, and delta lactams

Consider the three cyclic amides: $\beta$-lactam $\gamma$-lactam $\delta$-lactam My question What is the basic site (site of protonation) for these three lactams? And what should be their Brønsted ...
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Difference in acid strength of oxalic acid and malonic acid

Despite very similar skeletal structures, the difference in acid strength between oxalic acid (ethanedioic acid) and malonic acid (propanedioic acid) is quite significant. What is the reason for that? ...
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Proton transfer equilibrium in bisulphite adducts

In the addition of $\ce{NaHSO3}$ to aldehydes and methyl ketones (higher ketones do not respond well to this reaction), crystalline addition products are formed. An $\ce{-SO3H}$ and an $\ce{-OH}$ ...
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Obtaining activity coefficients of conjugate acids of some common carboxylic acid molecules

Recently, I have been wondering about justifying the notion on how some common acids (e.g. carboxylic acids) are themselves weaker bases than water to the point that we don't usually consider them to ...
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What is the word for how polyprotic an acid is?

What is the word to describe the number of acidic hydrogens an acid has? I am currently thinking something like "proticity", but I am not sure The use case world be for a table of things like this: <...
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Are all solutions of weak acid/bases buffers?

I am having a difficult time understanding what makes a buffer a buffer. Buffers in my textbook are defined as a solution of a weak acid or base and their conjugate acid/base. So if I were to just ...
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Why is carbon dioxide considered a Lewis acid?

$\ce{CO2}$ is considered a Lewis acid. How it is an acid? According to Lewis: “species that accept an electron pair are acids”. But $\ce{CO2}$ can't accept electron pairs because oxygen and carbon ...
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The pH of a neutralized solution

If pH is defined as the concentration of hydrogen ions in solution, then how can a ‘neutralized’ solution (defined as having an equal amount of hydrogen and hydroxide ions) have a pH other than 7? ...
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How can I make an acidic pen to burn paper on writing on it?

If I have a pen with refillable ink, can I just pour in concentrated Hydrochloric acid or concentrated sulfuric acid in the ink chamber to make it an acidic pen? Would it be better to use the acid of ...
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Activity of hydrogen ion

I am not from chemistry background. Could you tell me in simple words what the activity of hydrogen $a_{\ce{H+}}$ is? It arises in the context that the negative logarithm of the activity of hydrogen ...
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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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Oxalic acid structure

What is the reason why oxalic acid has its second $\ce{-COOH}$ group flipped? I'm guessing it's something to do with steric repulsions between the $\ce{-COOH}$ groups but I'm not sure.
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Peculiar deprotonation of an alkenyl proton

In this synthesis of Punctatin A, there is this peculiar deprotonation step. When subjected to the base $\ce {NaH}$, we would expect deprotonation at the $\alpha$-position, at the side opposite to the ...
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What are the limitations of the Hendersson-Hasselbalch equation?

Our instructor told us that prior to the equivalence point, the $\mathrm{pH}$ of a solution is dependent on the HH equation. However, when I tried practicing for polyprotic acid titration, I came upon ...
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Will using vinegar harm car paint?

After having parked my car in a newly constructed airport parking garage, I came back to find something had dripped through a crack in the ceiling of the structure and left considerably thick film on ...
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Why is H2S2O7 stronger than H2SO4?

I've read that for an oxyacid, the oxidation number of the central atom shows the power of that acid, but here, the oxidation numbers of sulphur in sulphuric acid and pyrosulphuric acid are both the ...
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Why should 2,6-Dimethyl-4-nitrophenol be more acidic than 3,5-Dimethyl-4-nitrophenol

I was trying to compare acidity of some organic compounds but can't understand some: Why should 2,6-dimethyl-4-nitrophenol be more acidic than 3,5-dimethyl-4-nitrophenol? I have been trying to ...
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Strong and Weak Acids/Bases

I'm so confused... $\ce{HClO}$ is a weak acid. then why is its conjugate base, $\ce{ClO-}$, a weak base in water? shouldn't they be inversely proportional? shouldn't $\ce{ClO-}$, be a strong base? ...
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Why is carbonic acid a weaker acid than acetic acid?

Is it because the $\ce{OH}$ group next to $\ce{COOH}$ in carbonic acid donates electron density to the $\ce{COO-}$ by resonance, making it a stronger base, compared to a weaker electron donating ...
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Is methanol really more acidic than water?

The question Why is methanol more acidic than water? deals with the reasoning of why methanol is more acidic than water. However, as mentioned in the comments of that question, the acidity constant of ...
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Weird Wikipedia Section on Oxidizing Behavior of Nitric and Sulfuric Acids

It has been my understanding that when nitric, perchloric, or sulfuric acids act as oxidizing agents, they must exist as whole $\ce{HNO_3}$ or $\ce{HClO_4}$ or $\ce{H_2SO_4}$ molecules that are still ...
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Acid-base equilibrium of NH4CN

I'm having difficulties understanding this problem. We have in the problem that $K_\mathrm a$ for $\ce{HCN} = 6.2\cdot10^{-10}$ and $K_\mathrm b$ for $\ce{NH3} = 1.8\cdot10^{-5}$. Write chemical ...
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Why is HCl a stronger acid than Acetic Acid?

Drawing the conjugate bases, Oxygen is more electronegative than Chlorine so negative charge on Oxygen is more stable than Chlorine, Thus My argument that Acetic Acid is more acidic. Also the O¯ ...
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What is the reason that tertiary alcohol pKa is higher than primary alcohol pKa?

A tertiary alcohol has a $\mathrm{p}K_\mathrm{a}$ of 18 while a primary alcohol has a $\mathrm{p}K_\mathrm{a}$ of 16. Shouldn't the tertiary alcohol be more acidic since its conjugate base is more ...
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Reactions of alkynes with sodium/ammonia vs sodium amide

What happens when alkynes react with sodium in ammonia ($\ce{Na/NH3}$), or when they react with sodium amide ($\ce{NaNH2}$)? Are these two sets of conditions different?
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Is Saliva an acid or base?

I have a debate with some friends who believe that saliva is just basic, but with the enzymes which make them reactive with objects in our mouth, shouldn't it be an acid in this case?
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Inductive vs resonance effects and the acidity of phenol

A lot of people rationalize the acidity of phenol by saying that resonance is responsible for much of phenol's acidity as opposed to aliphatic alcohols. However, this image suggests that in fact the ...
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Find the initial volume of the weak acid given a titration graph

Question: Below is a picture of a titration between a weak acid, $\ce{HA}$, and a 0.150 M $\ce{NaOH}$ solution. Find the initial volume of the weak acid in milliliters in this titration. My ...
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Why is the pKa (COOH) of alanine and glycine similar but the pKa (NH3) different?

Alanine is heavier with a ($\ce{-CH3}$) than glycine which has an ($\ce{-H}$). What makes them have different $\mathrm{p}K_\text{a}(\ce{-NH3+})$ $(\mathrm{p}K_\text{a}: \text{Ala}=9.69, \text{Gly}=9....
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Hydrogen halide acidity

Why is it that $pK_{\ce{a-HF}} \lt pK_{\ce{a-HCl}}\lt pK_{\ce{a-HBr}}\lt pK_{\ce{a-HI}}$, although the electronegativity decreases? The more electronegative the atom accompanying hydrogen, the lower ...
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Rate and mechanism of the reaction of Mg and HCl

In the reaction between hydrochloric acid and Magnesium the overall reaction is: $$\ce{Mg + 2HCl -> MgCl2 + H2}$$ My proposed mechanism of reaction is that $\ce{HCl}$ dissociates in $\ce{H2O}$ ...
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Why does ammonia act as an acid in only the first of these two reactions?

$$\ce{2Na(l) +2NH3 (g) ->2NaNH2(s) + H2(g)}$$ $$\ce{CH3Cl (alc) +NH3 (alc) -> CH3NH2 (alc) +HCl(alc)}$$ Doesn't ammonia donate a proton in both cases?
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Why is it that weak bases usually contain nitrogen?

Why do weak bases usually contain nitrogen? I know there are two electrons on top for a bond of $\ce{H}$ but why is it mostly nitrogen? I know there are other elemental bases too but why do I keep ...
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Why is benzoic acid a stronger acid than 3-aminobenzoic acid?

Why is benzoic acid a stronger acid than 3-aminobenzoic acid? Obviously at meta position, only negative inductive effect will operate. But, how does that make it a weaker acid than benzoic acid?
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Identifying a glass frosting chemical

I have purchased an "unknown" white coloured powder from the market which can frost glass objects. Here are some properties of this powder White in colour When mixed with HCL or water, it results in ...
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Most basic nitrogen in Adenine

I need to find the most basic site of Adenine: The $\ce{NH2}$ group and $\ce{NH}$ cant be strong base as electrons are delocalised. This leaves us with $1,7,3$. I thought that electron density on $1,...
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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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Why is benzoic acid a stronger acid than acetic acid?

Why is benzoic acid ($\mathrm{p}K_\mathrm{a} = 4.20$) a stronger acid than acetic acid ($\mathrm{p}K_\mathrm{a} = 4.76$), even though the conjugate base in case of benzoic acid is destabilized due to ...
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How is the yellow colour of nitric acid removed?

Nitric acid obtained in laboratory is slightly yellow due to the dissolution of nitrogen dioxide which is produced due to thermal decomposition of a portion of $\ce{HNO3}$. $$ \ce {4HNO3 -> 2H2O ...
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Questions about Buffer System (Lab)

I will be doing a lab on Hydrogen Phosphate buffer system tomorrow and I have a few questions about the buffer system. I am not sure if my assumptions are correct. (1) What would happen to the rate ...
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Why does the pH of soft drinks get lower as they go flat?

I am doing an investigation about the chemistry of soft drinks and as part of this I observed the effect of time on the pH of soft drinks fully expecting the pH to increase as the carbonic acid, a ...
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What is the relationship between the two definitions of the difference between basicity and nucleophilicity?

(Clarification: this is a question about terminology, not so much about when to use different concepts. I think I do understand which characteristics of a species to use when trying to determine ...
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How to prove that chloroform is more acidic than fluoroform? [duplicate]

How to prove that chloroform is more acidic than fluoroform? Using the concept that the inductive effect is dominant over the resonance (mesomeric effect) in the case of halide substituents: $\...
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What's the pH of vinegar containg 5% acetic acid?

Vinegar generally contains 5% acetic acid. We would expect the pH of vinegar to be approximately: a. 0 b. 3 c. 7 d. 9 e. 12 I don't have the key for this question, so I just want to make ...
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Why do strong acid-weak base reactions “essentially go to completion”?

This is what my textbook says. I understand that the strong acid would readily donate a hydrogen ion, but I can't see how all the weak base will readily accept it (at least not to "essential ...
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How is aqua regia stored?

How is aqua regia stored as it dissolves all metals?
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Should the 'a' in the acid dissociation constant (Ka or pKa) be capitalised?

In science, the negative logarithm of the acid dissociation constant is denoted $\mathrm{p}K_\mathrm{a}$ or $\mathrm{p}K_\mathrm{A}$ depending on the source (lowercase "a" or uppercase "A"). Since it ...

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