Skip to main content

Questions tagged [ph]

pH (or the potential of hydrogen) is a scale used to measure how acidic or basic an aqueous solution is.

Filter by
Sorted by
Tagged with
123 votes
7 answers
85k views

Is a negative pH level physically possible?

A friend of mine was looking over the definition of pH and was wondering if it is possible to have a negative pH. From the equation below, it certainly seems mathematically possible—if you have a $1.1$...
apnorton's user avatar
  • 1,349
54 votes
2 answers
12k views

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 ...
Horatio's user avatar
  • 649
45 votes
4 answers
53k views

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 ...
Eliza's user avatar
  • 2,413
34 votes
1 answer
24k views

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 ...
Dhruba Banerjee's user avatar
32 votes
2 answers
35k views

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:...
The Quark's user avatar
  • 597
31 votes
2 answers
56k views

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): $\...
studen's user avatar
  • 587
28 votes
1 answer
2k views

Why did the Rio 2016 pool water turn green?

One of the swimming pools at Rio 2016 Olympics has turned green: While proliferation of algae is a likely culprit, there have been some alternative explanations offered by local organizers. CNN has ...
F'x's user avatar
  • 23.7k
25 votes
2 answers
3k 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 ...
Dissenter's user avatar
  • 18.9k
25 votes
2 answers
13k views

Why does water dissociate to H3O+ and OH- rather than H+ and OH-?

Why does water dissociate to $\ce{H3O+ + OH-}$ instead of $\ce{H+ + OH-}$? This question came to surface when I was learning about acids and bases, and learned this definition: $\mathrm{pH=}-\log_{10}[...
Ell's user avatar
  • 383
24 votes
2 answers
30k views

Why are the majority of cleaning solutions basic?

When testing for pH for common household cleaning products, such as dishwasher fluid, I noticed that majority of them tend to be basic? Why is that? Do acid make good cleaning solutions as well?
user10037's user avatar
  • 341
22 votes
2 answers
5k views

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 ...
uhoh's user avatar
  • 5,788
21 votes
3 answers
16k views

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 ...
Gerard's user avatar
  • 3,451
19 votes
1 answer
66k views

How do I calculate the isoelectric point of amino acids, each of which has more than two values of pKa?

For most amino acids, the $\mathrm{pI}$ is simply the arithmetic mean of the amino and carboxyl $\mathrm pK_\mathrm a$s. However, for tyrosine and cysteine, which have more than one $\mathrm pK_\...
Andrew Wolf's user avatar
19 votes
1 answer
4k views

How can benzaldehyde have a pKa of 14.9?

There are numerous websites out there which claim that the pKa of benzaldehyde – C6H5CHO – is 14.90. (Just do a Google search for benzaldehyde pka to see what I ...
orthocresol's user avatar
  • 71.2k
18 votes
2 answers
3k views

Why are some pH standard solutions 6.86 and 9.18?

I have calibrated pH sensors in the lab on several occasions and have used standards of 4.0, 7.0 and 10.0 usually. Recently I received a sensor and was tasked to calibrate it, but it requested ...
en_lorithai's user avatar
18 votes
4 answers
53k views

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 ...
CrownedEagle's user avatar
18 votes
1 answer
4k views

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 ...
Deuterated's user avatar
17 votes
1 answer
17k views

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 ...
hello all's user avatar
  • 391
16 votes
1 answer
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}...
bobthejoe's user avatar
  • 2,400
15 votes
1 answer
8k views

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 ...
QCD_IS_GOOD's user avatar
  • 1,118
15 votes
4 answers
71k views

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 ...
Eliza's user avatar
  • 2,413
15 votes
4 answers
20k views

Is LiOH a weaker base than NaOH?

Is $\ce{LiOH}$ a weaker base than $\ce{NaOH}$? Note: I'm not interested in "why," but rather what the "real" $\mathrm{p}K_ \mathrm{b}$ values are. $$ \begin{array}{lcc} \text{Data for Alkali Metal ...
MaxW's user avatar
  • 22.2k
14 votes
5 answers
18k views

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 ...
Orcris's user avatar
  • 435
14 votes
1 answer
1k views

Is it possible to measure pH without physically coming into contact with a solution?

I've been researching ocean acidification, and the way that ocean pH is typically measured is by using sensors placed throughout all of the oceans. This is costly and time-consuming, and being able to ...
Noah's user avatar
  • 143
14 votes
2 answers
169k views

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 $\displaystyle\ce{NaHCO3 -> Na+ + HCO3-}$...
scrblnrd3's user avatar
  • 371
13 votes
2 answers
8k views

Why are synthetic pH indicators used over natural indicators?

Synthetic indicators seem to be exclusively used when determining the pH of a substance with an indicator (with the exception of that school experiment where you boil cabbage to demonstrate natural pH ...
Patrick Shway's user avatar
13 votes
4 answers
28k views

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 ...
Fixed Point's user avatar
13 votes
1 answer
11k views

Is the equation pH + pOH = 14 valid at different temperatures?

$\mathrm{pH} + \mathrm{pOH} = 14$ For water at 60 degrees Celsius, $K_\mathrm{w} = 1 \times 10^{-13} = [\ce{H+}] \times [\ce{OH-}]$ Hence, $[\ce{H+}] = 1 \times 10^{-6.5} = [\ce{OH-}]$ So $\...
K-Feldspar's user avatar
  • 2,853
13 votes
1 answer
18k views

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 ...
Ali Hasan's user avatar
  • 435
13 votes
3 answers
8k views

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{...
làntèrn's user avatar
  • 639
12 votes
5 answers
41k views

How to determine the pH of a mixture of two weak acids?

We have two solutions: Solution 1 is $\ce{HCOOH}$, its concentration is $c_1 = \pu{10^-2 mol/l}$, its volume is $V_1 = \pu{50 ml}$, and its $\mathrm{pH}_1 = 2.9$. Solution 2 is $\ce{CH3COOH}$, its ...
Hedwig's user avatar
  • 121
12 votes
5 answers
29k 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 ...
user2804925's user avatar
12 votes
1 answer
868 views

Do solid phase pH buffers exist?

I want to buffer the pH of my solution but I don’t want to add any mobile solutes. I imagine that large molecular mass buffers could be used such as phosphorylated polysaccharides or proteins. The ...
WaterMolecule's user avatar
11 votes
2 answers
47k views

What chemicals are in tap water that gives it a slightly basic pH level

In chemistry, we recently did a lab where we observed the different ways of reading pH of several different substances. We used things such as red cabbage juice, litmus paper, pH paper and a pH probe. ...
Cody Guldner's user avatar
11 votes
1 answer
2k views

Why measure both alkalinity and pH in pools if pH alone tells us how acidic or basic something is?

I am trying to better understand the chemistry of maintaining my pool so that I can use the least amount of chemicals to control algae growth and I'm confused by the need to measure both total ...
lurning too koad's user avatar
11 votes
1 answer
10k views

What are the side effects of adding dry ice to a swimming pool?

My apartment complex pool was closed today due to a resident dumping a large quantity of dry ice into the pool. In the notification from my landlord, they stated: Dry ice is frozen carbon dioxide ...
Cat's user avatar
  • 219
11 votes
3 answers
30k views

Why does the pH of soft drinks get lower as they go flat?

I am doing an investigation about the chemistry of soft drinks and as part of this I observed the effect of time on the pH of soft drinks fully expecting the pH to increase as the carbonic acid, a ...
1111's user avatar
  • 111
11 votes
1 answer
6k views

exchanging H2O in buffer for D2O - pH vs pD?

I have TBS pH 7.4 buffer that I am exchanging all the water out for $\ce{D2O}$. How do I find out what the pD is after all the water is gone? I understand that pH meters don't work for deuterium, and ...
oryza's user avatar
  • 133
10 votes
5 answers
50k views

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 ...
Asker123's user avatar
  • 3,050
10 votes
2 answers
56k views

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 ...
Josh Gray's user avatar
  • 260
10 votes
1 answer
2k views

Approximate time for pure water pH to equilibrate in open air?

I'm a complete non-chemist, so I don't know how to calculate this, or even what to google for (my searches yielded esoteric research papers). I'm doing some hobby experiments, and I'd like to know ...
Ranging's user avatar
  • 103
9 votes
2 answers
2k views

Why are almost all fruits acidic? [closed]

Almost all the fruits are acidic in nature, but why? At least, fruits like apples should be neutral right? But although apple is sweet, it is acidic. Why?
Ishaan Manish's user avatar
9 votes
3 answers
6k views

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? ...
ahorn's user avatar
  • 209
9 votes
2 answers
7k views

How to calculate pH of a solution when H3PO4, NaH2PO4, Na2HPO4 and Na3PO4 are mixed together in certain amounts to form a solution?

How to calculate pH of a solution when $\ce{H3PO4}$, $\ce{NaH2PO4}$, $\ce{Na2HPO4}$ and $\ce{Na3PO4}$ are mixed together in certain amounts to form a solution? I know how to calculate pH when they ...
user avatar
9 votes
1 answer
635 views

How was pH measured back in the day if you had nothing to calibrate to?

We learn about indicators but these seem awfully useless if you have no clue what pH the color change occurs at. How did early chemists figure this out? I guess more broadly, how was the hydronium ...
cheekylittleduck's user avatar
9 votes
3 answers
6k views

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}]}{[\...
Tony's user avatar
  • 91
9 votes
1 answer
8k views

Chemistry behind lip balm coloring based on skin pH

I stumbled across an ad for a clear, colorless lip balm that purportedly tints your lips a shade of pink determined by your skin's pH. This balm stain applies on clear then reacts with your skin's ...
Melanie Shebel's user avatar
9 votes
1 answer
3k views

Why is it that weak bases usually contain nitrogen?

Why do weak bases usually contain nitrogen? I know there are two electrons on top for a bond of $\ce{H}$ but why is it mostly nitrogen? I know there are other elemental bases too but why do I keep ...
Asker123's user avatar
  • 3,050
9 votes
2 answers
6k views

Is there a pH range for "neutral" detergents?

There exist many home made pH scales like these But do any of you know if there is an "official" scale that defines if a neutral detergent is 7 sharp or within a range _______?
Norfeldt's user avatar
  • 141
9 votes
1 answer
6k views

Is there a means to measure pH without indicators?

I have created a solution that should contain hydroxide ions. Therefore, the pH > 7, but is there any way to roughly estimate the pH in absence of any indicator? Maybe using current, or checking ...
user209347's user avatar

1
2 3 4 5
19