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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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Is a negative pH level physically possible?

A friend of mine was looking over the definition of pH, and wondering if it is possible to have a negative pH level. From the equation below, it certainly seems possible—just have a $1.1$ (or ...
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The reason behind the steep rise in pH in the acid base titration curve

Most books refer to a steep rise in pH when a titration reaches the equivalence point. However, I do not understand why … I mean I am adding the same drops of acid to the alkali but just as I near the ...
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1answer
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Calculating the pH of a highly dilute solution of HCl

For relatively high concentrations of $\ce{HCl}$, I usually just assume that $[\ce{H+}] = [\ce{HCl}]$, because $\ce{HCl}$ is a strong acid and is completely ionized in solution. By taking the negative ...
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The pH of a neutralized solution

If pH is defined as the concentration of hydrogen ions in solution, then how can a ‘neutralized’ solution (defined as having an equal amount of hydrogen and hydroxide ions) have a pH other than 7? ...
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1answer
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What is the pKa of the hydronium, or oxonium, ion (H3O+)?

Although the wikipedia page on Hydronium indicates a $\mathrm{p}K_\text{a}$ of −1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:...
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Does the number of H+ ions in solution go up on dilution of a weak acid?

In my textbook, a footnote says: In case of weak acids, on dilution the total number of $\ce{H^{+}}$ ions in solution increases because dissociation of the weak acid increases This didn't make ...
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Shouldn't the pH at the equivalence point always be 7?

I learned in class that the equivalence point in an acid-base titration is reached when the solution contains an equal amount of substance of $\ce{OH-}$ and $\ce{H+}$ ions. However, in a weak acid and ...
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pH probe bulb - what is happening within the glass?

I am trying to understand how the glass bulb of a pH electrode of a pH meter works - the glass bulb itself. Not the reference electrode or the rest of the electrode (HCl, Ag/AgCl wire, etc...), the ...
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1answer
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Effect of Temperature on pH of Water

The $K_\mathrm w$ is a function of temperature. It is $10^{-14}$ at $25\ \mathrm{^\circ C}$. When the temperature is $50\ \mathrm{^\circ C}$, the $K_\mathrm w$ can be calculated to be somewhere around ...
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What are the products of the dissociation of sodium bicarbonate in water? What is the relative pH of the solution?

I had a recent question on a test that asked what the products would be if sodium hydrogen carbonate were dissolved in water. I had a few candidate answers $\displaystyle\ce{NaHCO3 -> Na+ + HCO3-}$...
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Why is a buffer solution best when pH = pKa i.e. when A-/HA=1

Buffers work best when $\mathrm{pH}$=$\mathrm{p}K_\mathrm{a}$ From the Henderson-Hasselbalch equation, $\mathrm{pH}= \mathrm{p}K_\mathrm{a} + \log_{10}\left(\frac{[\ce{A-}]}{[\ce{HA}]}\right)$ If $...
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1answer
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How does the litmus pH indicator work?

I'm wondering about how does the litmus solution work as a pH indicator. And another question: When you put drops of litmus solution into an colorless acid (e.g. $\ce{HCl}$), it turns red. But then ...
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2answers
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How concentrated can an acid be?

How concentrated can an acid be without it being supersaturated? Is there a certain limit to how concentrated an acid or base can be? When I mean concentration, I mean molarity; so how concentrated ...
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What is the unit of pH?

I'm making some graphs and I have to label the axes. I want to be extra careful and put the units in even though the meaning of $\text{pH}$ is well known. But I have a problem (though a simple one): $\...
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3answers
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pH range outside conventional 0-14 [duplicate]

Is a pH value outside 0 - 14 possible? I asked my teacher who said: yes, it is, but very difficult to achieve. Then on the internet, I found multiple answers, one saying it is but because of a fault ...
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1answer
146 views

Is there any notion of pH out of solution?

For example, could one define a $\mathrm{pH}$ for pure acetic acid? It's a weak acid in water, but if someone handed you $1~\mathrm L$ of pure acetic acid, what would its $\mathrm{pH}$ be?
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1answer
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Chalcogens' hydrides as acids?

I've noticed that chalcogens never form binary acids, and instead end up like water, with very little acidity. Why is this? Or am I wrong and there's a counterexample, if so please give it.
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pH and materials selction [closed]

I working on the Navy study guide for their nuclear engineering programs and I am not a Chemist. Thus, I have come here to try and develop a better understanding of the subject matter. Why is pH ...
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1answer
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Why is buffer capacity at a maximum when the ratio of its components is 1? [duplicate]

A buffer consists of a weak acid and its salt or weak base and its salt. When the ratio of weak acid and its salt in a buffer (or the ration of weak base and its salt) is equal to 1, we say that the ...
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2answers
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Why will a strong acid neutralize as much base as a weak acid?

This is a simple concept that I can't seem to understand. Why will a strong acid neutralize as much base as a weak acid, if the acids are of the same volume and concentration? A strong acid will ...
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1answer
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What is the role of pH in azo coupling reaction of diazonium with phenol and aniline?

Why is it so that azo coupling with phenol needs basic pH (9–10) and with aniline it needs acidic pH (4–5). How does pH participate in the mechanism? I have searched the internet for quite a while ...
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How much can the pH change through dilution?

Consider an acidic solution with Hydrogen ion concentration, $\ce{[H+]}$ of $10^{-5}\:\mathrm{M}$. Since $\:\mathrm{pH} = -\log \ce{[H+]}$ the $\:\mathrm{pH}$ of solution is $5$. Suppose we dilute ...
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Determine the pH of mixture of two weak acids

We’ve two solutions : Solution 1 $\ce{HCOOH}$ its concentration is $c_1=10^{-2}\ \mathrm{mol/l}$ and its volume is $v_1 = 50\ \mathrm{ml}$ and its $\mathrm{pH}_1 = 2.9$ Solution 2 $\ce{CH_3COOH}$ ...
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Calculating the pH of a saturated calcium fluoride solution

How can I calculate the pH of a saturated solution of calcium fluoride ($\ce{CaF2}$)? I am given the following values: $$\begin{align} K_\mathrm{sp}(\ce{CaF2}) &= 3.9 \cdot 10^{-11} \\ K_\mathrm{...
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4answers
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Dissolving Organic Tissues [duplicate]

Watching some movie/TV this question came to mind, purely theoretical of course, if one wanted to dissolve a human corpse, like getting rid of a body after killing someone, is it better to use an acid ...
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3answers
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Calculating Buffer Capacity

I completed a titration of Ammonium Acetate buffer solution and to it I added $\pu{2M}$ Hydrochloric Acid. I measured the initial $\ce{pH}$ of the buffer solution before any acid was added and I ...
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1answer
1k views

Which pH approximation to choose when?

When I learned about pH approximations in school, I was told that each approximation fits to a certain acidity strength/pKa range. Those ranges are grouped in common categories (pKa borders are only ...
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1answer
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Acidic and alkaline salt solutions: why do some salt form acid/bases while others don't

I have a question regarding salts and their solutions. How come some salts, like sodium carbonate and ammonium chloride, produce acids/bases when dissolved in water? Moreover, how can you predict ...
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3answers
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What is the pH of 1M Glycerol?

If the pKa of Glycerol is 14.15. How do you calculate the pH for it? I assume that the Henderson-Hasselbalch derivative that works for weak acids and bases is not applicable here.
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1answer
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Finding pH of tri-protic acid

I am studying for my final and I am given this problem: A solution of sodium phosphate is made from 10.5 g sodium phosphate in 150 mL of water. What is the pH of this solution Given: Ka1, Ka2. ...
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What is the pH of ice?

The pH of pure liquid water depends on temperature. It is about pH = 7.0 at room temperature, pH = 6.1 at 100 °C, and pH = 7.5 at 0 °C. What happens to the pH (or to the ion product) of pure water ...
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2answers
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Calculation of the pH of a mixture of a strong acid and weak acid

The question is to find out the $\mathrm{pH}$ of a mixture of weak acid and strong acid. My book just states the formula as $$\mathrm{pH}=-\log \frac{C_2+\sqrt{C_2^2+4K_\mathrm{a}C_1}}{2}$$ where $...
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1answer
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Does dilution of a buffer affect pH?

The Henderson-Hasselbalch equation for the $\mathrm{pH}$ of a buffer solution of the monoprotic acid $\ce{HA}$ is given by $$\mathrm{pH}=\mathrm pK_\mathrm a+\log{\frac{[\ce{A-}]}{[\ce{HA}]}}$$ Since ...
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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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2answers
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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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3answers
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Is the Henderson–Hasselbalch equation volume independent?

Looking at this equation $\mathrm{pH} = \mathrm{p}K_\text{a} +\log\frac{[\ce{CB}]}{[\ce{A}]}$ makes me think that it is concentration independent. What I mean is, when we look at $\frac{[\ce{CB}]}{[\...
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1answer
958 views

Can the colour change in litmus paper be explained by conjugated systems?

I have been trying to understand the colour change in litmus paper on a more detailed level than "the chemical identity changes, and therefore also physical properties". I have knowledge of the ...
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2answers
1k views

How is the pKa of extremely weak acids determined?

According to Wikipedia, the conjugate acid of LDA has a pKa of about 35 - which is in line with figures I've seen elsewhere. How then can such a weak acid's pKa be determined? If the determination is ...
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1answer
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Why does depurination happen at a higher pH (or under less harsh conditions) than depyrimidation?

I've always wondered why the N-glycosidic bond, which connects the adenine or guanine purine bases to their sugars, was the easiest to cleave via acid hydrolysis, or why purines have the lowest ...
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1answer
3k views

Determining the pH of an organic solvent

Our work is faced with the issue of determining the charge of compounds that are dissolved in chloroform. One could realistically determine the charge of the relevant moieties knowing the $\mathrm{p}...
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5answers
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Why isn't water acidic?

The definition of an acid is a compound with a hydrogen cation and a non-metal anion. Water is a hydroxide bonded to a hydrogen atom. This hydroxide has a net negative charge, too, since the negative ...
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2answers
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pH of aqueous solution of HCl of low concentration [duplicate]

What is the pH of $10^{-8}~\mathrm{M}$ $\ce{HCl}$ solution in water? My attempt: pH = $-\log(10)^{-8}$ = 8 But this is wrong because it should be acidic. Where have I gone wrong?
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Why does pH affect fermentation?

I know that the lower the pH the faster fermentation occurs. Why does this happen?
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1answer
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Glass electrode pH measurement

How is the potential difference between the outer and inner surface of the glass bubble in a glass electrode measured if an Ag/AgCl wire is used as the indicator electrode and Ag/AgCl/KCl is used as ...
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3answers
14k views

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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2answers
18k views

MgCl2 acidic or neutral in water?

I'm currently taking chemistry 12. On our test we were asked, when given a $0.1~\mathrm{M}$ solution of certain compounds whether the resulting solution when added to water would be acidic, basic, or ...
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2answers
461 views

Dissociation of water into H+ and OH-: Does the law of mass action hold at nanoscale?

Suppose water under neutral conditions is confined in a virtual spherical nanocontainer with a radius of 25 nm. To calculate the number of hydronium ions, one uses water dissociation constant which is ...
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2answers
34k views

Does dissolving salt in water change the pH?

I am particularly interested in the effect or lack of effect of dissolved NaCl in regards to pH in water. It would be interesting also if anyone has any insight for other salts and their effects. ...
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1answer
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Calculating pH for titration of weak base with strong acid

Calculate the pH at the equivalence point for the titration of $\pu{0.130 M}$ methylamine ($\ce{CH3NH2}$) with $\pu{0.130 M}$ $\ce{HCl}$. The $K_\mathrm{b}$ of methylamine is ${5.0 \cdot 10^{–4}}$. ...
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2answers
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Bicarbonate decomposition and pKa [closed]

I want to understand why the p$K_{\mathrm a}$ of $\ce{HCO3-}$ is approximately 10.2 and not less. My hypothesis is this : Bicarbonate could react in two ways in an aqueous solution: $[1]\qquad\ce{...