Questions tagged [ph]
pH (or the potential of hydrogen) is a scale used to measure how acidic or basic an aqueous solution is.
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Solubility of iron(II)hydroxide [on hold]
Solubility of iron(II)hydroxide is $K_s = 1.0 · 10⁻¹⁴ (mol / dm³) ³$. How I calculate solubility of $Fe(OH)_2$ in buffer solution which pH is 10.54.
I know that $K_s = [Fe^{2+}][OH^{-}]^2$ and the $...
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1answer
69 views
What alkali and alkaline earth metal oxides will turn moist red litmus blue and finally white? [closed]
How many of the following will turn moist red litmus blue and finally white?
$\ce{Li2O}$, $\ce{KO3}$, $\ce{RbO2}$, $\ce{Cs2O2}$, $\ce{BeO}$, $\ce{MgO}$, $\ce{BaO2}$, $\ce{SrO}$.
Since bleach ...
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29 views
Dissociation equilibrium for nicotinic acid
Nicotinic acid is an amphoteric compound. Does it mean that in very low $\mathrm{pH}$ it will be more soluble?
Would the following be possible?
$$
\begin{align}
\ce{H2X+ &<=> H+ + HX}\\
\...
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0answers
47 views
What is the benefit of using a pH indicator reagent over pH strips or a meter?
I've recently started getting into chemistry a bit as a hobby. Nothing serious, just amateur level stuff mostly, primarily just to educate myself.
Whenever I need to determine the pH level of a ...
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1answer
42 views
Dissociation behaviour of polyelectrolytes
Assuming a solution of 100 polycationic molecules, each of them carrying 100 amino groups and an apparent pKa of 6.5. Would it mean that, at a pH of 6.5,
50 molecules will be fully protonated
50 ...
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2answers
52 views
What's wrong in this?
While calculating pH of 10^-8M HCl, we take into account the H+ ions released by water. But water also releases OH-ions.So she shouldn't they neutralise the H+ ions?
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2answers
109 views
Can an acid have a high pH? [closed]
I am studying anesthetics and came across thiopental which is considered a weak acid. However it has a pH of 10.5. I always learned that greater than 7 is alkaline. I’m looking for some guru to help ...
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1answer
44 views
Concentration of Hydrogen Ions
I am slightly confused about one certain task.
There are 4 different solutions ($\ce{NH3}$, $\ce{HCl}$, $\ce{NaOH}$, $\ce{CH3COOH}$), their concentration is the same $(c = \pu{1 mol L-1}).$ Which ...
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3answers
51 views
Solubility and pH
I was reading about antacids. It stated that in earlier times $\ce{NaHCO3}$ and a mixture of aluminium and magnesium hydroxide were used as antacids. In excess $\ce{NaHCO3}$ can make the medium ...
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Why does the pH of a reaction between magnesium and hydrochloric acid stay the same?
I did an experiment where I reacted magnesium with hydrochloric acid and tested the pH of the solution at the beginning and at the end. My pH paper told me that the pH did not change or at least very ...
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1answer
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pH of very dilute acids
From doing some research on the site I have found that many people have posted about solutions of $\ce{HCl}$ where $[\ce{HCl}] = \pu{1e-8 mol dm-3}$
Here they are able to deduce
$$[\ce{H+}] = \frac{[...
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2answers
56 views
Calculating dissociation degree from pH and Ka without given initial acid concentration
Is it possible to calculate the dissociation degree (DD) from pH and Ka without directly been given the initial acid concentration?
I found the following formula:
$$\text{DD} = \frac{K_\mathrm{a}}{...
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1answer
32 views
How to calculate the pH of a solution given the concentration and pKa's of solutes? [closed]
For example, if I have a solution of 50mM acetlycholine (pKa = 4.5), how would I go about calculating the pH of the solution?
Thanks
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1answer
29 views
pH change with temperature
I understand that the pH of solutions decreases as the temperature increases but is there a reason as to why some solution's pH decreases more than others even if the temperature change is the same?
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1answer
28 views
Evaluate mass of salt needed to add to a buffer solution knowing only pH
This is an exercise taken from an old exam, I'm struggling with the resolution.
To a solution of a generic weak acid $\ce{HA}$ were added $\pu{2.40 g}$ of a potassium salt of the $\ce{KA}$. The ...
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1answer
49 views
What could be causing noisy pH measurements?
I designed and built a hydroponics system with pH logging and I am trying to understand why pH measurements in the nutrient reservoir vary ~ ±0.2 pH while measurements in a separate bottle of probe ...
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1answer
24 views
Why must a buffer solution contain both a weak acid and a salt solution of its conjugate base?
Doesn’t the weak acid dissociate to produce the conjugate base on its own?
I understand that when a strong base is added to the buffer solution, the hydroxide ions will react with the hydrogen ions ...
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3answers
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Sugar solutions have a neutral pH in themselves, but it makes your body acidic. Why? [closed]
I'm not an expert, but as far as I understood a sugar solution is completely neutral since sugar can't take hydrogen ions out of the water or donate them in. Sugar is a non ionic compound, so it does ...
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1answer
134 views
Optimum pH range for formation of Schiff bases
What is the optimum range of pH for the formation of Schiff Bases by the addition of hydroxylamine to an aldehyde or a ketone?
According to Peter Sykes' A Guidebook to Mechanisms in Organic Chemistry,...
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1answer
30 views
Regarding acid-base reactions, how does one know when a hydrophobic base substance is fully protonated?
When there's a weak base substance (hydrophobic powder), and it needs to be completely protonated by adding an acid (eg: HCl), how does one know when it's completely protonated? Since the powdered ...
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0answers
38 views
Seeming discrepancy between pKa and corresponding Ka of methylamine
The first entry in PubChem for the $\mathrm pK_\mathrm a$ of methylamine is $10.657$ at $25\ \mathrm{^\circ C}$. My elementary understanding is that this would be found as the negative log of the $K_\...
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Understanding how the definitions of pH and activity are compatible
At $T=\pu{25 ^\circ C}$ and $P=\pu{1bar}$, the density of water is $\pu{0.997 kg L-1}$.
Neglecting nonideality of the mixture $\ce{H2O(l), H+}$ and $\ce{OH-}$ (all activity coefficients are close to $...
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1answer
43 views
Experimental determination of pH [closed]
I am trying to determine the experimental pKa for two weak acids that were titrated against 0.20M NaOH.
I have read elsewhere that you can take the point where the graph becomes steep and divide the ...
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2answers
103 views
When an acid is added to water, why does the hydroxide ion concentration decrease?
At equilibrium in pure water, we have
$$\ce{[H_3O+][OH-]} = 10^{-14}$$
Since $\ce{H3O+}$ and $\ce{OH-}$ ions are produced in pairs, we may conclude
$$\ce{[H_3O+]}=\ce{[OH-]} = 10^{-7}$$
So far so ...
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1answer
17 views
What are standard controllers for automatic pH control?
My background in control theory comes from electrical engineering (robots, motors, etc.) and I want to build a control system for automatic pH control.
Can I directly apply my knowledge from ...
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1answer
41 views
neutralization of a strong acid with a strong base [closed]
When a 1M H2SO4 is mixed with an equal volume of 1M NaOH, is the mixture acidic, basic, or neutral?
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1answer
38 views
How do I calculate the amount of polyprotic acid and base needed to achieve a certain buffer pH?
e.g. Citric Acid and Trisodium Citrate
$\ce{H3C6H5O7 <=>[ka_1] H2C6H5O7- + H+ <=>[ka_2] HC6H5O7^2- + H+ <=>[ka_3] C6H5O7^3- + H+}$
Using the definition of Ka and substituting for ...
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2answers
34 views
Does a solution of pH zero contain hydroxide ions? [closed]
Are there hydroxide ions in a solution of pH 0?
0
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1answer
143 views
Calculate mass concentration of Ca(OH)2 solution
Can anyone help me calculate the mass concentration of $\ce{Ca(OH)2}$ solution with molar mass $\pu{74.1 g/mol}$ at the $\pu{pH of 12.8}$.
My work so far:
From the pH I get the molar concentration ...
2
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1answer
49 views
pH throughout a titration
Estimate the $\ce{pH}$ of the solution that results when $\ce{75.0 mL}$ of $\ce{0.275 M HCl}$ is added to $\ce{50.0 mL}$ of $\ce{0.275 M Na2HPO4 (aq)}$.
My book gives the successive $\ce{Ka}$ values ...
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1answer
102 views
Why doesn't pH = pKa1 in the buffer zone for this titration?
Below is an image from my textbook representing the titration curve for the titration of $5.00\ \mathrm{mL}$ of $0.010\ \mathrm M$ $\ce{H2S2O3}$ with $0.010\ \mathrm M$ $\ce{KOH}$, which has $\mathrm ...
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1answer
35 views
Acid neutralization [closed]
I am working on a biogas plant,
digester volume 3000 liter,
right now pH condition is acidic at 4.00
my requirement is to maintain pH to 6.50 to 7.20
what should I do?
some suggestions are there like, ...
2
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0answers
37 views
Water values and water hardness
We have drinking water with the following values:
Calcium mg/l 62.7
Magnesium mg/l 10.3
total hardness 7.) dH 11.1
Total hardness 7) mmol/l CaCO3 1,99
Carbonate hardness °dH 8.5
...
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0answers
103 views
How to measure pH of deionized water
reverse osmosis deionized water (RODI) is used to rinse acid off silicon after it undergoes silicon etching. Sample of water is taken and measured by using pH meter. However, pH meter takes a 1-2 ...
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EQPt pH of a Monoprotic Acid-Base Titration: Product of Molarites Over Their Sum
Context
The Henderson-Hasselbalch equation is as follows. $$pH=-\log\big(K_a\big)+\log\bigg(\frac{[A^-]}{[HA]}\bigg)$$ One may follow its derivation in order to understand how it came to be, yet ...
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1answer
52 views
Confusion About Acid/Bases That Don’t Follow the Arrhenius Definition [closed]
I understand that acidity is merely a reflection of how many free hydrogen ions are in water, and basisicity is just a reflection of the number of hydroxide ions, but I don’t understand how this ...
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1answer
376 views
How to calculate pH of the Na2Co3 solution given ambiguous Ka values
This is the exact question i faced on exam.
Calculate the pH of $\pu{0.05 M}\ \ce{Na2CO3}\ (\ce{H2CO3}: K_\mathrm{a,1}= 4\times 10^{-7},\ K_\mathrm{a,2}= 4.7\times 10^{-11})$
Solution
$\ce{Na2CO3 -&...
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124 views
If Ti(NO3)4 is dissolved in water, what would be the change of pH?
Does this compound exist in nature. I would suppose the salt would dissolve in it's ions (Nitrate and $\ce{Ti+}$). Wouldn't the nitrate react with the hydrogen in the water and give us a acid? And ...
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2answers
332 views
Calculate pH of a weak acid and weak base neutralization reaction
I'm an industrial pharmacist needing some help with some chemistry basics.
I'm trying to calculate the theoretical pH of an effervescent preparation containing 2 mmol citric acid ($\ce{H3C6H5O7}$), 4 ...
3
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1answer
114 views
What is the pH of this H2SO4 solution? [duplicate]
I'm trying to solve a simple problem which is driving me crazy. It says:
Estimate the pH of a solution that contains 1 gram of $\ce{H_2SO_4}$ dissolved in 1 liter of water.
When I solve the ...
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0answers
57 views
Calculating the pH of a weak acid from the Kb of its conjugate base
I'd start off by saying it's been many years since I was in chemistry lessons and have forgotten much, but recently I have had to relearn a lot of basic chemistry. The following doesn't really impede ...
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2answers
399 views
The effect of pH and solubility on coagulation in water treatment
In water treatment, a specific pH range must be met in order for the process of coagulation to occur properly. Sources have stated this is due to the pH affecting the solubility of the coagulant, but ...
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37 views
Capacity of buffer
I want to dissolve 23 mg of EDC (N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride) in MES buffer with pH=6. How can I know the amount and concentration of MES buffer which can keep the pH=...
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1answer
47 views
Working out pH of solution when excess NaOH is added
In a pH titration, $30\text{cm}^3$ of $\ce{NaOH}$ is added to $\pu{20 cm3}$ $\ce{CH3COOH}$. The concentrations of both solutions was $\pu{0.5 mol dm-3}$. $K_\mathrm{a} = \pu{1.7 x 10^{-5}}$ for $\ce{...
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1answer
318 views
Finding the pH value of HF [closed]
Find the pH value of HF.
$pH = -\log[H+]$ for strong acids
$pOH = -\log[OH-]$ for strong bases
$pH = 1/2(pKa - \log C)$ for weak acid
$pOH = 1/2(pKb - \log C)$ for weak base
HF is weak acid so $...
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1answer
77 views
Safely lowering bleach pH without chlorine gas?
According to Eurekalert, by lowering the pH of household bleach (e.g., by adding vinegar or citric acid), we can increase $\text{[HOCl]}$ and consequently greatly improve the disinfecting capabilites ...
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1answer
345 views
What is the pH of starch?
We need to identify an unknown for a chemistry lab. It's either starch or zinc sulfate.
We know that zinc sulfate is acidic, but what is the pH of starch?
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1answer
2k views
Finding pKa from equivalence point on titration curve [closed]
Is there a mathematical proof/explanation of why $\mathrm{p}K_\mathrm{a}$ corresponds to the $\mathrm{pH}$ at $\text{Volume of titrant}/2$ at the equivalence point?
A concise proof will suffice.
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Buffer solutions
So my understanding of buffer solutions is that when a strong acid is added, it will react with the conjugate base to convert the strong acid to a weak acid. The weak acid then dissociates to reform ...
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1answer
281 views
Calculating PH of solution after adding strong acid (equilibrium)
Consider the classic example when talking about acids and bases:
Say you have 1M of $\ce{HCL}$ and you throw it into water, calculate the resulting pH (= concentration of $\ce{H3O+}$).
The way this ...
