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9 votes
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How to (numerically) model a phosphoric acid titration curve

Much easier is to calculate the inverse function $[\ce{Na+}]=f([\ce{H+}],K_\mathrm{a1},K_\mathrm{a2},K_\mathrm{a3})$. Calculate fractions of respective phosphate forms as the function of $\ce{[H+]}$ ...
Poutnik's user avatar
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8 votes

Am I understanding buffering capacity against strong acid/base correctly?

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 $\pm1$ ...
porphyrin's user avatar
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7 votes
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Why does "bis-tris propane" have two pKa values?

The compound "bis-tris-propane"(1,3-bis(tris(hydroxymethyl)methylamino)propane, also known as BTP) has 2 secondary amino groups and can be written as $$\ce{R-NH-R-NH-R}$$ which, both in ...
Poutnik's user avatar
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6 votes
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Finding final pH of the buffer solution without applying Henderson equation

As the amounts of substance in the final solution are known to be $n(\ce{NH3}) = \pu{2 mmol},$ and $n(\ce{NH4^+}) = \pu{0.5 mmol},$ you may simply use the definition of the constant $K_\mathrm{b}:$ $$...
Maurice's user avatar
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6 votes
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Am I understanding buffering capacity against strong acid/base correctly?

User porphyrin is correct that buffer capacity is defined as the number of moles of strong acid or strong base needed to change the pH of 1 liter of solution by ±1 unit. The buffer capacity is a ...
MaxW's user avatar
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5 votes

What's the effect of temperature on buffering capacity?

Mathematically For a buffer solution containing a weak acid and its salt with a strong base, buffer capacity is given by $$\beta = 2.303 ( [\ce{H+}] + [\ce{OH-}] + \frac{C_{buff}.K_{\mathrm{a}}.[\ce{H+...
Adithya's user avatar
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5 votes

Why does "bis-tris propane" have two pKa values?

Why, with symmetric functional groups, are there two equilibrium constants? If the functional groups are close together, there will be electrostatic interactions (coupling). Adding the first proton (...
Karsten's user avatar
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4 votes

Am I understanding buffering capacity against strong acid/base correctly?

The purpose of buffers is to keep $\mathrm{pH}$, with the differential buffering capacity $\frac { \mathrm{d[B]}}{ \mathrm{d(pH)}}$ If you are interested in the integral buffer capacity across $\...
Poutnik's user avatar
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4 votes
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How to calculate bicarbonate and carbonate from total alkalinity

If I understood your question correctly, you have solutions where you know there is a given amount of calcium carbonate dissolved, and would like to know the distribution of this carbonate between all ...
ksousa's user avatar
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4 votes

How to (numerically) model a phosphoric acid titration curve

The R code equivalent of Poutnik's answer, for refrence: ...
Naiky's user avatar
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4 votes
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What is the math behind the formula for the concentration of the strong titrant when calculating theoretical buffer capacity of a diprotic system?

The equation that you have derived (the last one you show) \begin{equation} \frac{K_\mathrm{a1}\mathrm{[H_2A]}\left(\mathrm{[H_3O^+]}+2K_\mathrm{a2}\right)} {\mathrm{[H_3O^+]^2}} = \color{blue}{\...
Metal Storm's user avatar
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4 votes

Effects when 100 mmol NaHCO3 are mixed with 50 mmol HCl

Your second idea is right, the acid partially neutralizes bicarbonate. $$\ce{HCO3-(aq) + H3O+(aq) -> H2CO3(aq) + H2O}$$ It is effectively the buffer $\ce{HCO3-(aq)/CO2(aq)}$, as $\ce{H2CO3(aq)}$ ...
Poutnik's user avatar
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3 votes

Is mixture of ammonium hydroxide and ammonium nitrate a buffer solution?

A buffer is a mixture of a weak acid with the conjugate weak base. Is a mixture of $\ce{NH4OH}$ and $\ce{NH4NO3}$ a buffer solution? I have seen some examples with $\ce{NH4OH}$ and $\ce{NH4Cl}$ but ...
Karsten's user avatar
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3 votes

What is total concentration of buffer used in derivation of buffer capacity?

Initially in the solution the following equilibria exist $$\ce{HA <=> H+ +A-}$$ and $$\ce{H2O <=> H+ +OH-}$$ Let initial concentration of $\ce{HA}$ be $a_1$ and that of $\ce{A-}$ be $a_2$. ...
Adithya's user avatar
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3 votes
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Why is sodium bicarbonate added to lower the pH?

Poutnik has given an excellent answer to your question: Why $\ce{NaHCO3}$ is able to lower the $\mathrm{pH}$ and what is the reaction that occur when I add it? It is also important that your ...
Mathew Mahindaratne's user avatar
3 votes

Why is sodium bicarbonate added to lower the pH?

This answer addresses the original interpretation of the question "Why $\ce{NaHCO3}$ ?“ rather than "Why to lower pH ?“. For the latter, see the Mathew's answer. The reason of using $\ce{...
Poutnik's user avatar
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3 votes

How to Prepare a Buffer Solution?

Here is what you would do in the lab (2 recipes, depending on your needs): You start by diluting the concentrated ammonia to about $\pu{100 m}\mathrm{\small M}$. Then, while measuring the pH, you add ...
Karsten's user avatar
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3 votes
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How to Prepare a Buffer Solution?

You have some of the chemistry wrong. Looking at your assumptions, concentrated ammonia is typically in aqueous solution, as is concentrated hydrochloric acid. You could have ethanol solutions ...
MaxW's user avatar
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3 votes
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How exactly does a buffer made up of a weak acid and its conjugate base work upon addition of hydroxide ions?

During neutralization of the buffer by a strong base solution, there are ongoing three reversible reactions, maintaining three equilibria: $$ \begin{align} \ce{H2O + A- &<=> OH- + HA} &\...
Poutnik's user avatar
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3 votes
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pH of PBS after adding acetic acid

Yes. Adding $5$ mL pure acetic acid to $50$ mL phosphate base saline (PBS) produces a pH value situated between $2$ and $3$, depending upon the exact concentrations of the phosphates of the PBS. ...
Maurice's user avatar
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3 votes

pH calculation of a mixure containing 2 strong acids and a buffer mixture

First, you have to allow the strong acids to react with the weak base. $$\ce{HCl + NaOAc -> HOAc + Na+ + Cl-}$$ $$\ce{HNO3 + NaOAc -> HOAc + Na+ + NO3-}$$ This goes to completion. As a result, ...
Karsten's user avatar
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3 votes

What happens when you add a weak acid to a solution buffered at a pH of 8.0?

Weak acids at a concentration of 10 mmol/L and the given range of p$K_\mathrm{a}$ values dissociate very little in pure water. How much it dissociates in a buffered solution depends on the pH of the ...
Karsten's user avatar
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2 votes
Accepted

Why does Calcium (specifically Calcium Carbonate) inhibit the Citrate buffer system?

"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}...
Poutnik's user avatar
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2 votes

Can I make a buffer with a weak acid without adding it's conjugated base, when the desired pH of the solution is exactly the pKa of the weak acid?

So your solution is already at a pH equal to the pKa of the weak acid you are about to add. Your hunch is that the pH remains the same after adding acid to a solution. [...] we will end up with ...
Karsten's user avatar
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2 votes

Calculating ratio of conjugate base and acid when pH and pKa are given

Recall the fundamental properties of the logarithm $$+\log \left(\frac{a}{b}\right)$$ is the same as $$-\log \left(\frac{b}{a}\right)$$ so Henderson Hasselbach can have plus or minus signs. The ...
AChem's user avatar
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2 votes
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How to calculate pH of an CH3COOH solution?

I have asked OP to verify the solution concentration but didn't get the answer. Thus, I assume it is $8\% \ (w/w)$. Thus, if you assume $[\ce{HA}] = c$ then: $$ c = 8\% \ (w/w) = \frac{\pu{8 g}\text{ ...
Mathew Mahindaratne's user avatar
2 votes

Calculating the pH of a 'buffer' solution?

Question: Determine the $\mathrm{pH}$ of the solution resulting when $\pu{100 cm^3}$ of $\pu{0.50 mol dm-3}$ $\ce{CH2ClCOOH}$ is mixed with $\pu{200 cm^3}$ of $\pu{0.10 mol dm-3}$ $\ce{NaOH}$. I'm ...
Mathew Mahindaratne's user avatar
2 votes

buffer "recipe" needed

A pH buffer at pH $6.2$ can be made in $4$ Liters water, by dissolving $\ce{104.8 g KH2PO4}$ plus $\ce{5.44 g NaOH}$. Adding $\ce{NaOH}$ will simply transform part of the dihydrogenophosphate ion into ...
Maurice's user avatar
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2 votes

Prepairing a Sodium Acetate buffer - Meaning of molarity

It is the molarity of total acetic acid/acetate content, so the 3rd option. It is quite general principle applied in the pH buffer context. You can have a wide rage of $\ce{pH}$ values with the ...
Poutnik's user avatar
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2 votes

How to make NaxPO4 buffer?

The Cold Spring Harbor protocol is probably fine. There is another recipe that uses a mixture of potassium and sodium salts (for better solubility). 50 mM NaxPO4, pH 8 (and 0.5 M NaCl) This is a ...
Karsten's user avatar
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