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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17
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3answers
3k views

Does nitrogen inversion affect the basicity of amines?

If I were to compare the basic strength of 1-azabicyclo[2.2.1]heptane and triethylamine: Can I say that 1-azabicyclo[2.2.1]heptane is more basic than triethylamine because the lone pair of electrons ...
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1answer
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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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3answers
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Why is it considered acid rain with pH <5.6?

I recently read in a book that rain is considered acid rain if the pH falls below 5.6. However a substance is acidic when the pH is below 7; so why is the boundary for acid rain 5.6? I was thinking ...
14
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1answer
135 views

How sure can we be about the structure of purine?

While answering the question Basicities of nitrogen atoms in purine, I noticed, that there might be a rapid interchange of the hydrogen bonded to the nitrogen atoms. I have found a crystal structure ...
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Why isn't water acidic?

The definition of an acid is a compound with a hydrogen cation and a non-metal anion. Water is a hydroxide bonded to a hydrogen atom. This hydroxide has a net negative charge, too, since the negative ...
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Why isn't dry CaCl₂ used to dry HCl gas instead of concentrated sulfuric acid?

In our chemistry books, it is said that concentrated sulphuric acid is used to dry $\ce{HCl}$ gas. But, concentrated sulphuric acid is a strong oxidising agent so, why isn't $\ce{HCl}$ gas oxidised ...
12
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How do I calculate the degree of dissociation in equilibrium?

In my textbook, for calculating the percentage dissociation of $\ce{HF}$ for the given equation: $$\ce{HF + H2O <=> H3O+ + F-}$$ The solution is: Initial Concentrations $$[\ce{HF}] = 0.08~\...
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Is sulfuric acid or hydrochloric acid stronger?

Of my belief, sulfuric acid might be a little stronger than hydrochloric acid. Because even though they both are strong acids, one mole of sulfuric acid produces two times as much $\ce{H+}$ as one ...
11
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Which is more basic, hydrazine or ammonia?

Which of the following will be more basic, hydrazine $\ce{H2N-NH2}$ or ammonia $\ce{NH3}$? My chemistry teacher said that $\ce{NH3}$ is more basic since after giving $\ce{H+}$ to hydrazine results in ...
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More acidic - protonated carbonyl or protonated hydroxyl?

Consider two acetic acid derivatives, one with a protonated carbonyl oxygen and one with a protonated hydroxyl oxygen. An argument for the one with the protonated hydroxyl oxygen being more acidic ...
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Can “Common Ion Effect” suppress the dissociation of water molecules in acidulated water?

$$\begin{align} \ce{H2O &<=> H+ + OH-} \\ K &= \frac{[\ce{H+}][\ce{OH-}]}{[\ce{H2O}]} \\ \ce{H2SO4 &<=> 2H+ + SO4^2-} \end{align}$$ In acidulated water water dissociates into ...
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Reaction of aluminium trichloride with water

Since $\ce{Al^3+}$ is an acidic cation, shouldn't it react with water like this? \begin{align} \ce{AlCl3 + 6H2O &<=> [Al(H2O)6]^3+ + 3Cl^-} \tag1\\ \ce{[Al(H2O)6]^3+ +H2O &<=> ...
8
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1answer
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Is metallic sodium a strong base?

Chemical properties: Sodium metal and sodium amide ($\ce{NaNH2}$ ) are strong bases. They react with ethyne to form sodium acetylide with the liberation of hydrogen gas. How can a metal considered a ...
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Why do strong acids have weak conjugate bases?

This question is based on the Brønsted-Lowry model. I saw many answers to similar questions online. However none of them have given a detailed answer that is based on molecular structure (the answers ...
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Short Cut Method to Calculating pH of Polyprotic Acid?

I am doing the following question: Calculate the pH of a $4.00\ \mathrm{mol\ L^{-1}}$ solution of citric acid. $\mathrm{pK_{a1}} = 3.09~~~~~ \mathrm{pK_{a2}} = 4.75~~~~~ \mathrm{pK_{a3}} = 6.40$ ...
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Why is CF3COOH exceptionally acidic?

The pKa values of almost all carboxylic acids lie much above 0. But this is violated by trifluoroacetic acid(-0.25). How can this be justified?
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1answer
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How are these compounds strong bases, when they are sparingly soluble in water?

How is it possible that some insoluble compounds in water, e.g. $\ce{Mg(OH)2}$, $\ce{Ca(OH)2}$, $\ce{Sr(OH)2}$ are considered strong bases? Are they even strong bases? How can I tell if a compound is ...
6
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1answer
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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 $\rm +I$-...
6
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2answers
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Why is ortho-hydroxybenzoic acid more acidic than its para-isomer?

Why is ortho-hydroxybenzoic acid $(\mathrm{p}K_\mathrm{a} = 2.98)$ more acidic than its para-isomer $(\mathrm{p}K_\mathrm{a} = 4.58)$? March's Advanced Organic Chemistry (7th ed) gives the reason to ...
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3answers
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Can aluminum and hydrochloric acid be used to generate hydrogen gas?

I am looking to produce hydrogen gas in a small amount with supplies I currently have. Most of the methods I have seen involve reacting zinc or magnesium with $\ce{HCl}$ to obtain the gas, but I do ...
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2answers
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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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1answer
363 views

Formation of carbonic acid from breath?

Is it possible that blowing on water (hot/cold) can cause a reaction between the $\ce{CO2}$ from expiration and the water, to form $\ce{H2CO3}$? Is $\ce{H2CO3}$ dangerous?
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How do you explain pKa to non-professional?

Let's say we have substance $\ce{A}$, which is mixed with substance $\ce{B}$ to improve shelf-life because $\mathrm{p}K_\mathrm{a}$ of the substance $\ce{A}$ is $7.9$ and in mix the $\mathrm{pH}$ is $...
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1answer
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Can acidified or neutral KMnO4 oxidise toluene to benzoic acid?

Why is alkaline $\ce{KMnO4}$ used in the oxidation of toluene to benzoic acid? Can acidified or neutral $\ce{KMnO4}$ be used in this conversion?
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1answer
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Why can't the conjugate base of benzoic acid be stabilized by conjugation with the aromatic ring?

All the carbon and oxygen atoms are sp2 hybridised and can have a p orbital in the correct plane yet only conjugation of the COO- group occurs. I can't think why. I can't draw resonance structures for ...
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1answer
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How can a dilute acid dissociate more than a concentrated one? (Ostwald dilution law)

According to Ostwald's dilution law, the degree of dissociation of an electrolyte is inversely related to the concentration of it. $$ \alpha = \sqrt{\frac{K_a}{C}} $$ This means that a dilute acid ...
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2answers
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Why aren't neutralisation reactions reversible?

Let's take $$\ce{3HCl + Fe(OH)3 -> FeCl3 + 3H2O}$$ This would be a normal one-way neutralisation reaction. How about hydrolysis of ferric chloride (technically iron(III) chloride)? $$\ce{FeCl3 + ...
3
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1answer
733 views

Predicting pH of an acidic salt of an weak acid and weak base

Suppose we want to calculate pH of an $\ce{NH4HCO3}$ solution of known concentration. Now, $\ce{NH4+}$ will be hydrolised to give $\ce{H+}$ ions. Some $\ce{HCO3-}$ ions will be converted to (i) $\ce{...
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1answer
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How and why can more volatile acids be made with sulfuric acid? [duplicate]

I have read that sulfuric acid has low volatility. Then it states that more volatile acids can be made using sufuric acid and their corresponding salts, because of the low volatility. Can you help me ...
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3answers
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Why is meta-nitrophenol less acidic than para-nitrophenol? [closed]

My professor said while explaining the acidic nature of phenol that meta-nitrophenol is less acidic than para-nitrophenol, and gave the reason that resonance doesn't play on meta, but I didn't get it.
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1answer
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Why is quinoline less basic than pyridine?

Quinoline is less basic than pyridine, even though it has more resonating structures. Why? Does the negative inductive effect reduce basicity of quinoline?
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1answer
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Can reaction of gastric acid with swallowed things be dangerously exothermic?

Okay, okay. I know that swallowing a large enough amount of any substance would be considered dangerous. That isn't the point of this question, however. As you probably know, the stomach has ...
14
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3answers
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Why are weak acids weak?

What are weak acids? My chemistry and biology classes skimmed over them briefly but nothing in depth. I understand that an acid is weak if it partially dissociates and breaks down into ionic compounds,...
13
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1answer
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Can H4O 2+ form?

Like $\ce{NH4+}$ ,Is there any possibility of formation of $\ce{H4O^{2+}}$ (of tetrahedral structure)? My theory is: it can be formed by osmosis setup where heavy acids like $\ce{H3PO4}$ or $\ce{...
13
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If caffeine is an alkaloid, why is coffee acidic?

I have just put together on my mind these two facts: caffeine is an alkaloid and brewed coffee is slightly acidic (pH = 5). My Biology teacher and my Chemistry teacher could not elaborate satisfying ...
13
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1answer
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Nucleophilicity/basicity in protic and aprotic solvents

In polar aprotic solvent, why is $\ce{F-}$ a stronger nucleophile than $\ce{I-}$? What I think: If I talk about their basicity, $\ce{F-}$ would be more basic due to instability from its high electron ...
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3answers
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Why are acids usually depicted in fiction as green?

In cartoons, etc., acid is generally shown as vividly green, as in this scene from the Simpsons: We even have the colour "acid green". But when I used to use acids in chemistry class, they weren't ...
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1answer
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How is it possible to quantify the strength of a Lewis acid/base?

When the $pK_a$ scale is not applicable - when there is no proton/charged species transfer - what should be used to quantify the strength of an acid?
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1answer
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Acidity order of 4-halophenols

How do I theoretically predict the acidity order of the following para-halophenols? (experimental $\mathrm{p}K\mathrm{a}$ values beside each) parafluorophenol (9.92) parachlorophenol (9.41) ...
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2answers
370 views

Is there a terminology contradiction about whether the conjugate of a strong acid is a “weak base”?

(Please note, I am not simply asking, "Is the conjugate of a strong acid a weak base?" I'm asking about the contradictory ways those terms seem to be used.) I was revisiting strong/weak acids/bases ...
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Is oxalic acid dihydrate considered a primary acid standard in analytical chemistry?

Using oxalic acid dihydrate as a primary standard just seems really odd to me. I'd expect a primary standard to be oven dried. It just seems weird that a hydrate would be used. Granted, I saw ...
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Why amino acids (Zwitterion) become either negative or positive at low and high pH solutions?

The amino acids are Zwitterions. In neutral pH, an Amino acid's amino group has a postive charge and Carboxyl group has negative charge. They cancel each others charge thanks to the $Hydrogen$ that's ...
6
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2answers
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MgCl2 acidic or neutral in water?

I'm currently taking chemistry 12. On our test we were asked, when given a $0.1~\mathrm{M}$ solution of certain compounds whether the resulting solution when added to water would be acidic, basic, or ...
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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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0answers
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How does a 5th hydrogen bind to carbon atom in CH5[+]?

Can we bind a fifth hydrogen to a carbon atom if carbon is not in excited state? We have a big discussion in class and cannot clearly answer the question. If carbon atom excites an electron from $2\...
6
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1answer
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Buffer formation in weak acid/strong base titration?

I'm a little confused about what happens when you titrate a weak acid or base. For example, let's say that you are trying to titrate a weak acid. Based on this question, it seems like the weak acid ...
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0answers
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Is there a way to force C-protonation of an enolate?

In another question, I mentioned that O-protonation of an enolate followed by tautomerization may lead to increased amounts of the thermodynamic product over the kinetic product (when those are ...
5
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1answer
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Shape of Weak-Strong Acid-Base Titration

I can understand why in any titration, the pH changes really quickly near the equivalent point. However, in a titration of either weak base-strong acid or weak acid-strong base, the weak acid/base ...
5
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1answer
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Calculating pH for titration of weak base with strong acid

Calculate the pH at the equivalence point for the titration of $\pu{0.130 M}$ methylamine ($\ce{CH3NH2}$) with $\pu{0.130 M}$ $\ce{HCl}$. The $K_\mathrm{b}$ of methylamine is ${5.0 \cdot 10^{–4}}$. ...
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2answers
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Hydrogen bonding relating to molecular orbital theory

In [1, p. 232] here is an explanation of how alcohols hydrogen bond to each other and I do understand how the alcohols form hydrogen bonds to each other: FIGURE 6.15 Water and alcohols are ...