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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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8
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2answers
846 views

Why proton concentration is divided by 10⁻⁷?

I am reviewing the book Biochemistry Concepts and Connections by Appling, Cahill, and Mathews and I cannot understand why they divide by the hydrogen concentration by $10^{-7}$. Why not just leave it ...
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0answers
42 views

How can I preserve chlorophyll for long periods of time?

I'm currently working on a XIX century photographic process called Anthotype. It relies on organic colored substances that fade when exposed to sunlight. For the substances I've tried alcoholic ...
5
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2answers
112 views

Should the tip of the burette of an automatic titrator be immersed in the analyte?

In all the tutorials I found online, the tip of the burette (containing the titrant - NaOH) was immersed into the analyte solution. My question is: shouldn't the tip be out of the solution? Isn't ...
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2answers
117 views

What are the concentration changes when diluting an equimolar acetic acid: acetate buffer?

When a buffer (for example, a mixture of 100 mM acetic acid and 100 mM acetate), is diluted 10-fold, all the concentrations change drastically. Surprisingly, after re-establishment of equilibrium, the ...
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1answer
97 views

How is preparing a buffer possible?

I understand the concept of an equilibrium buffer solution, however I am a bit hung on how creating it doesn't shift the weak acid equilibrium. $$\ce{CH3COOH + H2O <=> CH3COO- + H3O+}$$ $$ K_\...
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1answer
548 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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0answers
186 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 ...
1
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1answer
46 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 ...
-4
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2answers
63 views

What's wrong in this? [duplicate]

While calculating pH of $10^{-8}$M HCl, we take into account the $\ce{H^+}$ ions released by water. But water also releases $\ce{OH-}$ions.So she shouldn't they neutralise the $\ce{H+}$ ions?
0
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2answers
137 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 ...
1
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1answer
72 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 ...
0
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3answers
75 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 ...
1
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1answer
120 views

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{[...
1
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2answers
302 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}}{...
-1
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1answer
54 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
1
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1answer
143 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?
0
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1answer
99 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 ...
3
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1answer
64 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 ...
1
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1answer
59 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 ...
3
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3answers
6k views

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 ...
2
votes
1answer
330 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,...
0
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1answer
39 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
60 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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0answers
44 views

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 $...
0
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1answer
54 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
420 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 ...
2
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1answer
22 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
61 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
64 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
41 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
403 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
56 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 ...
1
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1answer
256 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 ...
-1
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1answer
47 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
47 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 ...
0
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0answers
29 views

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 ...
-1
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1answer
147 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 ...
0
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1answer
4k views

How to calculate pH of the Na2CO3 solution given ambiguous Ka values

This is the exact question I faced on an 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{...
5
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2answers
681 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
1k 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 ...
1
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0answers
64 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 ...
0
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2answers
1k 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 ...
0
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1answer
117 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
2k 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 $...
1
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1answer
150 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
2k 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?
1
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1answer
6k 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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1answer
463 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 ...
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1answer
149 views

Determining volume of acid needed to be added to reach a specific pH

Suppose there are $\pu{0.024}$ moles of $\ce{Na2HPO4}$ in a $\pu{0.250L}$ solution. How would we calculate the amount of $\pu{0.145M}$ $\ce{HCl}$ needed to reach a $\mathrm{pH}$ of 6.60? I have ...
-2
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1answer
125 views

Find the concentration of proton after adding a acid to NaOH [closed]

I have this simple problem that I cannot figure out though, only the first part. 100 ml of 1.0 $\frac{mol}{L}$ $NaOH_(aq)$ contains ( a ) g of NaOH. After mixing 100 ml of 1.0 $\frac{mol}{L}$ $...