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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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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Calculating the pH of a dilluted aqueous KOH solution

Calculate $\mathrm{p}\ce{H}$ of an aqueous solution of $0.01\:\mathrm{nM}~\ce{KOH}$ in water. I think that water also has $\ce{OH-}$ ions in concentration of $10^{-7}\:\mathrm{M}$ (since $\mathrm{p}\...
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Which of mono-, di-, triphenylmethane is the most acidic?

Question How would you compare the acidity of the most acidic proton in each of the following molecules? diphenylmethane toluene triphenylmethane The answer says 3 is the most ...
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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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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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Comparing pKa of hydrocarbons

We have to compare their acidic strength, and we know acidic strength is directly proportional to stability of the anion. So the first compound is more acidic due to its being aromatic after ...
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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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What is the meaning of cmmol in chemistry?

I came across a unit called $\text{cmmol dm}^{-3}$ in buffer solutions. What does this unit mean?
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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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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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What is the acid dissociation constant of cacodylic acid?

What is the $\mathrm pK_\mathrm a$ of cacodylic acid? I cann't seem to find one answer on the internet. I have read 1.67, 6.37, and 4.8 in my $\mathrm pK_\mathrm a$ table. What is the reason for this? ...
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Why does ammonia accept a hydrogen to form ammonium when its octet is already complete?

Why does ammonia accept a hydrogen to form ammonium when its octet is already complete as $\ce{NH3}$ and it should be, seemingly, stable as $\ce{NH3}$?
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Basicities of nitrogen atoms in purine

Arrange the sites in purine in order of basicity. I feel that 9 is the least basic as nitrogen's lone pair is delocalised. However, I am unable to rank 1, 3, and 7 in a particular order. Is ...
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What exactly is basicity?

In my textbook, it’s given that the trend of the basicity of the elements of group 15 is $$\ce{NH3 > PH3 > AsH3 > SbH3 \ge BiH3}$$ Also, it’s said that the reducing character decreases down ...
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Why will CuSO4 solution be acidic?

An end-chapter problem posed in an 11-grade texbook asks to analyse whether a water solution of CuSO4 will be acidic. The standard answer is yes, because "$\ce{H2SO4}$ is a strong acid, hence $\ce{...
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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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Which is more basic: 1,2‐dihydropyridine or 1,4‐dihydropyridine?

Which compound is more basic of the two? My thinking: In compound A, the lone pair of nitrogen are in resonance with two other double bonds. The resonance chain here seems to be longer as ...
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Why is d3-acetic acid more acidic than acetic acid?

The following table is from Solomons, Fryhle and Snyder Organic Chemistry, chapter 3, An Introduction to Organic Reactions and Their Mechanisms: Acids and Bases: Table 3.8 Isotopic substituents and ...
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Comparing acidity of anilinium ion and para-fluoro anilium ion

Which of these compounds - anilinium ion and para-fluoro anilium ion - is more acidic? I thought the answer would the be first one since $\ce{-F}$ is an ortho-para activating group, so the electron ...
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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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Which species dissociate completely in ionic equations?

I am tasked with writing a molecular equation, an overall ionic equation, and a net ionic equation for the reaction between an aqueous solution of phosphoric acid, $\ce{H3PO4{(aq)}}$ and an aqueous ...
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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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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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Acidity of cyclopentadiene when fused to benzene rings

Why does fusion to a benzene ring reduce the acidity of a cyclopentadiene ring? For example, acidity decreases going from cyclopenta-1,3-diene to indene and to fluorene:
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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 to calculate the pH of an acetic acid/ calcium acetate buffer?

Problem: A buffer was made by mixing $\pu{500 mL}$ of $\pu{1 M}$ acetic acid and $\pu{500 mL}$ of $\pu{0.5 M}$ calcium acetate. What are the resulting concentrations of acetic acid (henceforth ...
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Fitting titration curve

To simulate the action of gastric $\ce{HCl}$, we have titrated 100 ml of a meal with 0.1 N $\ce{HCl}$. To plot the data, use (R-code) ...
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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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Why does nitric acid have a different molecular structure from phosphoric and arsenic acids?

I remember that this really bugged me as an undergrad, and upon revisiting some inorganic chemistry notes I realized I still don't have a satisfactory answer for it. The structure of nitric acid, $\ce{...
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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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Why do these two calculations give me different answers for the same acid-base titration?

In class, I performed an weak acid-strong base titration using commercial white vinegar and sodium hydroxide with the aim of finding the concentration of of ethanoic acid in the vinegar, and I used ...
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Why would the loss of H₂ to space mean that the Earth's geochemistry would be based on acid/base reactions?

I am reading a paper[1] that contains the line: Most of the $\ce{H2}$ in the Earth's mantle escaped to space early in the Earth's history; consequently, the overwhelming majority of the abiotic ...
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Why is acetone less acidic than cyclohexanol?

The $\mathrm{p}K_\mathrm{a}$ of acetone is 19, whereas the $\mathrm{p}K_\mathrm{a}$ of cyclohexanol is 16. However, acetone is resonance stabilized and its major resonance structure displays the ...
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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 &<=> ...
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Is the behavior of a dilute strong acid the same as the behavior of a weak acid?

My assumption is yes, as the $\mathrm{pH}$ levels of each will be similar and thus they have the same acidity. Is this correct or am I missing something?
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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 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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How does ammonium chloride increase the solubility of magnesium hydroxide in water?

In my textbook it is written that $\ce{Mg(OH)2}$ is slightly soluble in water, and it forms a milky solution which is called "milk of magnesia". Its solubility can be increased by the addition of $\...
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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 ...
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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 are lactate and lactic acid used synonymously in biochemistry?

In science there's always a misuse of the two terms. I know that lactate is the conjugate base of lactic acid. Why are they used like is the same thing? For exemple: in lactic acid bacteria (LAB) ...
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Choice of base for malonic ester synthesis

Most reaction mechanisms use $\ce{EtO-}$ as a base to deprotonate the alpha hydrogen in the malonic ester sythesis. But in the equilibrium there are still esters that haven't been deprotonated. Why ...
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Is calcium chloride an acidic or basic salt?

What I reason: Calcium chloride is the salt of hydrochloric acid and calcium hydroxide. Calcium hydroxide is usually not considered a strong base, and I believe this is because of it's low solubility. ...
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Why can the acidic strength between H2S and HCl be explained on the basis of electronegativity but H2S and H2O can't?

Consider simply aqueous solutions of $\ce{H2S}$ and $\ce{HCl}$ . It is pretty much known that $\ce{HCl}$ is stronger than $\ce{H2S}$ in water. The reason behind that first is the electronegativity of ...
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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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Combining acid dissociation constants to determine pH of diprotic acid

If I have a diprotic acid with $K_{\mathrm{a1}}$ and $K_{\mathrm{a2}}$ as the acid dissociation constants, why can't I calculate the final $\mathrm{pH}$ using $K = K_{\mathrm{a1}}\cdot K_{\mathrm{a2}}$...
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Why isn't N2 a Lewis base?

Why is $\ce{N2}$ (dinitrogen) not a Lewis base even with two lone pairs?
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Storing large quantities of KOH

I need to handle large quantities of $\ce{KOH}$; close to 1000 liters of 85 % conc $\ce{KOH}$ for about an hour. Any suggestions on how I go about doing it? Also the temperature during the process ...
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How does aqua regia dissolve gold?

I recently learned that aqua regia can dissolve less reactive or noble metals like gold. Aqua regia is a mixture of $\ce{HCl}$ and $\ce{HNO3}$, but separately, neither of these acids dissolve gold. ...
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Why is p-methoxyphenol more acidic than p-methylphenol?

Why is p-methoxyphenol more acidic than p-methylphenol? According to me, inductive effect really doesn’t matter at para positions and p-methoxyphenol should be less acidic due to the high mesomeric ...

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