New answers tagged

4

User porphyrin is correct that buffer capacity is defined as the number of moles of strong acid or base CB needed to change the pH of 1 liter of solution by ±1 unit. The buffer capacity is a dimensionless number. The buffer capacity is a somewhat fuzzy number in that the number of moles of base to cause + 1 pH change may not be the same as the number of ...


4

Further to the answer by Poutnik the buffer capacity $\beta$ of a weak acid - conjugate base buffer is defined as the number of moles of strong acid or base $C_B$ needed to change the $p$H by $\pm1$ unit, where $$\displaystyle \beta=\frac{d[B]}{d\text{pH}}$$ and the equilibrium concentration base present is $\displaystyle \mathrm{[B]}=\frac{k_w}{\mathrm{[...


3

The purpose of buffers is to keep $\mathrm{pH}$, with the differential buffering capacity $\frac{ \mathrm{d(pH)}}{ \mathrm{d}n}$ If you are interested in the integral buffer capacity across $\mathrm{pH}$ range, than optimal is the buffer with the maximum capacity in the middle of the range. But the useful range for a single pair buffers is usually just ...


-2

In the bonds $M^{z+}-O-H$, where $M$ can be $Mn$ or $Cr$, the atom $M$ is positively charged. When this charge $z$ is large, $M$ repells the $H$ atom stronger than if z is small. So the molecule containing these bonds is a stronger acid. For example, $Z$ = $6$ in $H_2CrO_4$ and $Z = 7$ in $HMnO_4$. They both contain at least one $M-O-H$ bond. As $Z$ is high ...


-2

Suppose you start from 1 Liter of a 0.1 molar solution of CH3COOH. The pH is 2.88. If you add 0.1 mole of NaOH, the pH goes to 4.74. The change is + 1.86 If now you start from a mixture 1:1 of 0.1 M CH3COOH and 0.1 M CH3COONa, the pH will be 4.74. Now if you add the same amount as above, 0.1 mole of NaOH, the pH will go to : 4.74 + log(0.2/0.1) = 5.05. The ...


0

Here's my method for looking at it: For determining acidity, we need to look which one of $\ce{H2SO4}$ or $\ce{HNO3}$ form a more stable anion after the $H+$ is extracted. Lets condsider $\ce{H2SO4}$ first- • There are two sites to extract a proton. • After a proton is removed, the $O-$ is in resonance with 2 oxygen atoms attached to the sulfur atom. ...


0

You're right they're difficult to use in organic reactions because of the solubility problem you mention. However, by using crown ethers like dibenzo-18-crown-6 they can be captured and the crown ethers are subsequently dissolved so that the bases are "brought into solution" and react.


0

The important thing about acidity is the stability of the conjugate base, which is enhanced by resonance effect and inductive effect. The more stable the conjugate base, the easier deprotonation becomes, and thus the stronger the acid. In a $\ce{NO3^-}$ ion, the negative charge can delocalise among three O atoms, but in a $\ce{HSO4^-}$ ion, in addition to ...


-2

Important information before understanding the reason for steric inhibition of resonance and the ortho effect In general, resonance stabilizes a molecule. But in the case of carboxylic acids, the conjugate base (anion after losing $\ce{H+}$) there are two equivalent resonance structures. Take the example of acetic acid, $\ce{CH3COOH}$, and thus acetate ion, ...


4

The following articles suggest that the data reported from Solomons, Fryhle and Snyder Organic Chemistry is likely incorrect. Maya Paabo, Roger G. Bates and R. A. Robinson ("Dissociation of Acetic Acid-d3 in Aqueous Solution and Related Isotope Effects from 0 to 50°", J. Phys. Chem. 1966, 70, 2, 540-543) report that the $\mathrm{p}K_\text{a}$ of the ...


0

One direct argument supporting answer (a) is that aqueous aluminum ions, in the presence of nitrate anions, apparently can undergo polynuclear hydrolysis liberating $\ce{H+}$, albeit as a function of the solution's pH and concentration. Per of an article 'Hydrolysis of aluminum(III) ion in sodium nitrate medium', to quote from an abstract: At a definite ...


3

Aqueous solutions In aqueous solution, $\ce{H+(aq)}$ and $\ce{OH-(aq)}$ are always present because of the autoionization of water: $$\ce{H2O(l) <=> H+(aq) + OH-(aq)}$$ So in aqueous solution, I would be comfortable saying there is an "association between $\ce{H+}$ and acidity, and between $\ce{OH-}$ and basicity". When the two concentration are ...


4

TL;DR Contrary to what the answers/comments have suggested, I would say that no reaction happens here. The acid–base reaction between the two given species is thermodynamically unfeasible, with an equilibrium constant $K \sim 10^{-9}$. If you want an acid-base reaction to occur between A and B, it's no use comparing the $\mathrm pK_\mathrm a$ values of ...


-1

Seven mistakes in seven lines !! Caleb is of course allowed to write down any sorts of equations. It is not forbidden by law. The trouble is that it is no use creating equations for reactions that simply do not happen in the reality. For example, 1) $Pb$ does not react with $HCl$, as he imagines. It does not react at all. 2) A mixture of $HCl$ and $...


0

Per a 2017 article from the Journal of Molecular Liquids some interesting comments. Yes, you can use HCl albeit in conjunction with a chlorate (or bromate or iodate..) and added chloride, to quote: It has been found that mixtures between sodium chlorate and HCl (NaClO3 + HCl ⇆ HClO3 + NaCl) in 20 mL are effective media for the dissolution of pure gold-...


2

The $\ce{O}$ atom in the $\ce{O-H}$ bond is more electronegative than $\ce{H}$ atom leading to a slight shift of the electron density towards the $\ce{O}$ atom and the development of a small negative charge, $\delta-$ on oxygen atom and $\delta+$ on hydrogen atom. Now, a water molecule also has an oxygen atom which attracts some electron density towards ...


4

Yours is a historical question. Note that in modern chemistry, it is not required that acids have H+ or bases have OH-. The words acidity or basicity referred to certain common behaviors such as acids will liberate hydrogen when come in contact with metals, or they will decompose carbonates to carbon dioxide. Similarly, bases had other common characters. ...


-1

In the molecule $\ce{CH3COOH}$ there is a final bond $\ce{-O-H}$ on the right hand-side of the molecule. This bond is made of a doublet of electrons and the bond is not very strong. Apparently the $\ce{H}$ atom, or better the $\ce{H}$ atom without its electron, i.e the ion $\ce{H+}$, is attracted by the next molecule of the solvent $\ce{H2O}$, and may quit ...


1

Galvanizing by definition is zinc coating. The zinc boils off ( as 1700 F) is approached and immediately oxidizes to ZnO , a white powder. ZnO has the unusual characteristic of causing zinc chills = brass founders ague = oxide shakes, IF inhaled while less than one hour old . After that is is pretty harmless and used in various lotions and creams and ...


0

My speculation on the possible mechanics of redox reactions that could move Cr into higher oxidation states upon welding with galvanized-steel. Understanding the chemistry may be instrumental in providing guidance. To begin, welding creates, in addition to heat, CO2 and water vapor (from the flame), which could act on the Zn coating creating hydrogen (and ...


0

Acid strength is determined by the stability of the conjugate base. Here are the factors that influence stability of the conjugate base: Ion size (when going down the rows of the periodic table) Electronegativity (when going in the same row of the periodic table across) Resonance Inductive Effects If you look at the conjugate bases, in acetic acid, the ...


1

The equations don't tell you the complete story, just as by looking at an equation one cannot predict the boiling point of HCl, in the same way we cannot say how many HCl or acetic acid molecules are dissociating in water. In easy words, if you had 0.1 moles of HCl in 1 L of water, all of them will dissociate in water, however if you have acetic acid, then ...


1

"Inhibited" is not probably the right term, as there is no catalyst inhibition, affecting the reaction kinetics. If we consider about neutral $\mathrm{pH}$ range, the citrate buffer keeps $\mathrm{pH}$ by equilibrium reactions $$\ce{HA^2- <=> H+ + A^3-}$$ $$\ce{HA^2- + OH- <=> H2O + A^3-}$$ with $\mathrm{p}K_\mathrm{a3}=6.4 $ Carbonate as a ...


0

Cement is basically made of impure $Ca_2SiO_4$, which is made of independent $Ca^{2+}$ and $SiO_4^{4-}$ ions. When mixed with water, the following reaction happens : $$Ca_2SiO_4 + H_2O \unicode{x2192}Ca(OH)_2 + CaSiO_3$$ The useful part of this final mixture is $CaSiO_3$ which has the structure of a polymer made of a long chain $H-O-(-Si(O^-)_2-O-Si(O^-)...


3

Ignoring activities, activity coefficients, ionic strength effects, and so on, I get a pH of around 9.3. Given the 1 M concentration, I would not bet a lot of money on this, though. My solution, assuming a more typical solution concentration, is given in the two figures below. Sorry these are figures rather than proper formatting: I have been away for 3 ...


1

The basic nature of amines is mostly dependent on their ability to donate their lone pair rather than stability of the conjugate acid formed. B, due to steric hindrance, does not undergo Amine Inversion. The lone pair is thus stationary and more prone to donation. Hence, B is more basic than A.


1

The mechanics of the reaction on Pb with concentrated HNO3 likely commences as follows: $\ce{Pb -> Pb(II) + 2 e-}$ $\ce{HNO3 = H+ + NO3-}$ $\ce{Pb(II) + 2 NO3- = Pb(NO3)2}$ $\ce{H+ + e- = .H}$ $\ce{.H + NO3- = OH- + .NO2}$ (1997 Source) The literature also contains citations (see, for example, Page 37) of an associated mechanism involving ...


0

Question It is an experimental fact that the pH of 1 M Na2S is essentially the same as the pH of 1 M NaOH. Based on this information, is S2− or HO− the stronger Bronsted-Lowry base? How can you tell? Assumptions Questions asked as part of a course usually lack context for people not taking the course. The question does not state which solvent was ...


2

This is an answer to a question of mine, which I posted a few days ago, Deprotonated form of phenolphthalein. I found this paper (it's in Japanese, but the relevant things are legible) https://www.jstage.jst.go.jp/article/yakushi1947/117/10-11/117_10-11_764/_pdf, which says that phenolphthalein has 2 pKas, pKa1 = 9.05 and pKa2 = 9.50. It also says that the ...


3

I found this paper (it's in Japanese, but the relevant things are legible) https://www.jstage.jst.go.jp/article/yakushi1947/117/10-11/117_10-11_764/_pdf, which says that phenolphthalein has 2 pKas, pKa1 = 9.05 and pKa2 = 9.50. It also says that the pink form is the twice deporotonated; the 1- form exists, but is colourless.


1

In the case of o-nitrophenol, the acidic hydrogen is hydrogen-bonded to the nitro group's oxygen atom, making it less acidic. In the case of catechol, one acidic hydrogen is hydrogen-bonded to the adjacent OH group's oxygen atom, but the other, more acidic hydrogen is not hydrogen bonded. This hydrogen is more acidic than that of hydroquinone. The resulting ...


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