Ph Definition and 520 Threads

In chemistry, pH (, denoting 'potential of hydrogen' or 'power of hydrogen') is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic or alkaline solutions.
The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution. This is because the formula used to calculate pH approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions in the solution. More precisely, pH is the negative of the base 10 logarithm of the activity of the H+ ion.At 25 °C, solutions with a pH less than 7 are acidic, and solutions with a pH greater than 7 are basic. Solutions with a pH of 7 at this temperature are neutral (e.g. pure water). The neutral value of the pH depends on the temperature – being lower than 7 if the temperature increases. The pH value can be less than 0 for very strong acids, or greater than 14 for very strong bases.The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or a color-changing indicator. Measurements of pH are important in chemistry, agronomy, medicine, water treatment, and many other applications.

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  1. N

    Henderson Hasselbalch Equation - Request for Clarification

    I understand the HH equation as: ##pH = pKa + log\frac{[A^-]}{[HA]}## The Numerator of the fraction is the conjugate Base of the original acid. The denominator is the undissociated/ unprotonated Acid. I understand that when the pH equals the PkA, then the solution is 50% dissociated, so...
  2. P

    Understanding the Effect of pH on Benzoic Acid Solubility

    Suppose we put benzoic acid in a buffered solution at pH=2. In this condition, it will be almost completely unionized and therefore not very soluble. Conversely, if it is placed in a basic environment, the solubility will be high. But why does this happen? Is there a shift in the acid...
  3. T

    Groundwater Chemistry on an Island

    Good day all! I have a question about groundwater chemistry on an island. We have datasets over the last 40+ years and what can be seen is that the eastern and western side of the island differ from each other. On the western side there has been a distinct drop in pH over the last decades, and...
  4. FlyingWhale

    Biology Sketch the change of pH in the breakdown of proteins into amino acids

    The pH stays the same because the optimum pH of trypsin is around pH 7.5. I think??
  5. barryj

    How does a swimming pool test kit measure pH levels?

    Swimming pool test kits combine a few drops of an unknown chemical with about 10 mL of pool water and then check the color of the reaction. I would like to know the chemistry behind this. I assume that the H+ and/or the OH- ions combine with some cheemical to produce the color to be checked...
  6. samy4408

    Something that doesn't make sense to me about calculating the pH

    Hello , the problem that i refer to is present when we try to calculate the pH of a solution without any assumption. in a lecture entitled "calculating the pH of a strong acid/base solution " after adding a certain amount of HCl in water we are asked to calculate the pH (the amount of HCl and...
  7. irumi

    How do I calculate the pH of slime and its effect on viscosity?

    How would I be able to calculate the pH of slime? I learned how to "add" pH's, like I know how to get a new pH from adding one solution to another. But I'm not sure on how to calculate the pH of slime. From what i know so far, this is all I will be making to make the slime: (Poly – Vinyl...
  8. StarChem

    Liming Lakes: A Solution for Acidification?

    I calculated it and found that is approximately 610Kg needed of CaCO3 to bring the lake pH to a neutral level. Is my calculation right 1st :)? Then if this is right, 610kg of CaCO3 is not that much in a matter of cost or weight to help the bio-life of the lake. I'm wondering if we are applying...
  9. marcelo

    How Much Calcium Carbonate to Add for Optimal pH in a Fish Tank?

    Considering a fish breeder decided to breed small fishes which needs a pH between 6,0 to 7,0 to stay alive. He needs to adjust the water's pH that is 5,0 to a value of 6.5, having available only calcium carbonate. The mass in mg added to 5L of water is about: A)2,5 B)5,5 C)6,5 D)7,5 E)9,5
  10. I

    Chemistry PH Indicator and Endpoint Observations

    A weak base is titrated with a strong acid. I think that both B and C are correct. The endpoint volume will be lower than the actual equivalence point volume. When the student mistakenly assumes the endpoint volume is the equivalence point volume, the number of moles of strong acid is seen as...
  11. Justinboln

    Chemistry Calculating Concentration of Acid using a pH Titration Curve

    Use the equivalence volume from the pH curve to calculate the concentration of the acid, HA. I'm not sure which equation to use or how to approach this question (Attached). Please elaborate on the steps on how to answer the question. Thank you!
  12. B

    Chemistry How much NaOH I have to add to increase pH?

    Hi everyone, I'm stuck in solving this problem. I have two solution of H2SO4 5M that needs two consequential pH increasing: the first from the natural pH of H2SO4 5M (around zero) to pH 2 and then from pH 2 to pH 7. The second solution from the natural pH of H2SO4 5M to pH 2 and then from pH 2...
  13. Boltzman Oscillation

    Are ISFETS available for cheap or am I out of luck

    I was looking into measuring the ph levels of a lake nearby where I live. I wanted to tie the experiment to my electronics coursework so I did some reasearch and found the wonder electronic that is the ISFET. Unfortunately, I cannot find anywhere to buy an ISFET transistor; I can easily find...
  14. P

    Chemistry Solving for electron activity given pH and ratio of redox elements

    I've written out the half reaction 8e- + 9H+ + SO42- = HS- + 4H2O and I know the logK = 4.25 (that's the constant mentioned in the prompt) I've written out the equilibrium statement of 10^4.25 = ([x^1/8]*[H2O^1/2])/([10x^1/8]*[e-]*[(10^-8.2)^9/8] However, from there, it seems like I have two...
  15. G

    Calculate the HCl concentration in H2O from the conductivity

    Hi y'all, I think this is my first time in the chemistry section of this forum, so thank you in advance for your patience with what is (I'm pretty sure) an elementary question. I've googled around for this a bit, but my last acid chemistry study was in 2002 or so, so the reading I am doing is...
  16. BillTre

    CO2 reduction driven by a pH gradient

    In the world of Origin of Life hypothesizing, there now seem to be two main competing approaches. Life originating at alkaline hydrothermal vents and an origin in intermittent terrestrial pools (exposed to periods of drying) getting outflow from volcanically heated water sources. The alkaline...
  17. Kaushik

    Chemistry Finding the pH of this acid and its sodium salt solution

    For finding the pH of the acid, I made use of the equilibrium law (or the law of mass action) to arrive at the degree of dissociation which I later used to get the [H+] concentration. I am stuck in finding the pH of the salt solution. ##CH2ClOO^- + H2O <---> CHClOOH + OH^-## Could you please...
  18. H

    Having trouble understanding pH = pKa + log([A-]/[HA])

    So I have a problem with the equation: pH = pKa + log([A-]/[HA]) The textbook states that when [H+] = Ka, there will be 50% A- and 50% HA. However, this won't work when the coefficients of the reactants to the products are not the same. The equation only works for reactions where it is a 1:1...
  19. TytoAlba95

    Biology Estimating pH Without [H+][A-]: Is There Another Way?

    How can we estimate the pH when the [H+][A-] is not provided. Is there some other formula?
  20. D

    Do these half-reactions have electrode potential that depends on pH?

    Do following half-reactions have electrode potential that depends on pH? I know H+ or OH- ions wouldn't be included in Nernst equation for these, but would pH affect chemical balance in these reactions, and therefore electrode potentials? Br2+2e- -> 2Br- Cl2+2e- -> 2Cl- I2+2e- -> 2I- S2O8+2e-...
  21. S

    Concentration of both buffers is the same, only the pH is different

    Here I used Henderson Hesselbach equation in both the cases , I.e pH= pKa + log( [(PO4)3-]/ [H3PO4]) here pKa of phosphoric acid is 2.16 but the problem Is in both the cases the log part is same and Pka is also same so both will cancel out, and how can we solve? It is confusing.
  22. S

    Correlating pka and pH with ionic forms (exercises)

    I have the following molecule: benzotriazole. It has pka=12. At pH=6 which form prevails? a) neutral b) anionic c) cationic d) none of the above. I thought the correct answer was c) cationic: pH<pka, benzotriazole has basic functional groups (amines).
  23. M

    Help! Aquaponics Garden pH Too High - Need Advice!

    Hi everyone, hoping for some quick help. I’m trying to get the chemistry right for an aquaponics garden I’m building. I screwed up pretty bad the first time and just swapped out almost 100% of the water (there was a residual 2-3 gallons in the bottom of the growbed). Last night added in about...
  24. D

    Calculating the pH of a Buffer Solution

    Hi everyone. I'm doing the multi-step problem above, and I've found myself stuck at part 3. For step 1, I determined that the equation that we're dealing with is: $$CH_3CH_2CO_2H + H_2O ⇔ CH_3CH_2CO_2^- + H_3O^+$$ I've also determined that the molar mass of propanoic acid is about 74.08g/mol...
  25. S

    Determining the Highest pH for Acid Solutions

    Homework Statement I am just a little confused about how the question is worded. It asks: Which of the following solutions would have the highest pH? Assume that they are all 0.10 M in acid at 25 C. The acid is followed by its Ka value. the bolded is what I don't understand. I don't know what...
  26. D

    Calculate the pH Slope using 7.0 and 10.0 buffers

    Hi, I'm trying to calculate the slope of a pH probe using 7.0 and 10.0 buffer solutions. I've been searching for hours but all examples use 7.0 and 4.0. I've calibrated my probe using the 7.0 and 4.0 buffers and calculated the slope, then I used 7.0 and 10.0, used the same math for the slope and...
  27. J

    Determining Solubility in Acidic Solutions / Pure Water

    Homework Statement How many of the following would you NOT expect to be more soluble in acid than in pure water? FeS, CuCN, AlPO4, BaCO3, AgCl Homework Equations None necessary The Attempt at a Solution So we know that anything with OH- or anything that has the conjugate base of a weak acid...
  28. J

    Determining if the pH changes when a chemical is added

    Homework Statement The question asks, how many of the following statements is/ are correct. I want to know which ones are right (I don't know the answer, but I will give a guess). BaCl2 added to an HCL solution does not change the pH NaBr added to an HBr solution will raise the pH. NaC2H3O2...
  29. S

    PH of citric acid solution at different concentrations

    What is the PH of 20%, 40% and 60% concentration of the citric acid solution?
  30. ChristinaMaria

    The relationship between pH and pOH at 70 ◦C/ 343.15 K

    Homework Statement The relationship between pH and pOH, for pure water, at 25 ◦C is 14 = pH + pOH What is the corresponding relationship between pH and pOH, for pure water, at 70 ◦C? Homework Equations Le Châtelier's principle? [H+][OH-] = 10-14 [10-7][10-7] = 10-14 (25 ◦C) [10-n][10-m] =...
  31. M

    Disolving NaCl in deionized water gives high pH value

    Hello I have a problem when I dissolves NaCl in deionized water. I have a pH probe in my deionized water (lets say 1 L). Then I add 40 g of NaCl, imidiately the pH-value rises to about 9.0 (i'm logging hte pH value as a function of time). Then slowly the pH-value lowers, and after 11 hours ...
  32. L

    Calculating pH with and without ionic strength

    Homework Statement There are four things to be calculated: -pH of 0.00196M solution of HCl in water, without taking ionic strength into account, -The same thing but taking ionic strength into account -pH of 0.00196M solution of HCl in Na2SO4, without taking ionic strength into account, -And...
  33. Krushnaraj Pandya

    Calculate pH change of a basic buffer

    Homework Statement to 1 L solution containing 0.1 mole each of NH3 and NH4Cl, 0.05 moles of NaOH is added. The change in pH will be? (pK for NH3=4.74) The Attempt at a Solution I have the solution and the answer is 0.48. The following was the first step calculated initial pH from henderson's...
  34. Krushnaraj Pandya

    How Does Pre-existing CH3COONa Affect Buffer pH Calculation?

    Homework Statement Calculate pH of a solution containing 0.1 mole of Ch3cooh, 0.2 mol of CH3COONa and 0.05 mol of naoh in 1 L. (Pka for Ch3cooh=4.74). 2. The attempt at a solution The 0.05 mol of NaOH will react with the 0.10 mol CH3COOH to produce 0.05 mol CH3COONa , and there will bve 0.05...
  35. opus

    B Why is pH a negative logarithm?

    I'm going over applications of logarithms in my College Algebra class and I'm at a part where it talks about pH scales, and it shows the pH concentration of a substance to be the negative logarithm of hydronium ions. I want to know why the logarithm is negative, so I googled it and the answers...
  36. D

    How a pH Probe Works: A Comprehensive Guide

    Homework Statement How does a pH probe work? Homework EquationsThe Attempt at a Solution A combined pH probe is comprised of 2 electrodes a measuring and reference electrode. The measuring electrode is composed of glass with a silver alloy electrical wire submerged into a neutral KCl solution...
  37. J

    Which of the following aqueous solutions would test closet to pH 7

    Homework Statement >Which of the following aqueous solutions would test closet to 7 on the pH scale? $a) NaCl$, $b) Na_2CO_3$, $c) NaH_2PO_4$, $d) NaCN$ Homework EquationsThe Attempt at a Solution I don't understand this. So I tried writing chemical equations like for a), NaCl + H20 --> NaOH +...
  38. chemisthypnos

    Observe pH Damaged Cells Via Microscope?

    For an upcoming research project, I intend to apply different solutions to cultures of cells. How would I determine if the cells are incurring damage from the solutions due to the pH of the solutions as I observe them under my compound microscope?
  39. J

    Calculate pH of NaF Solutions | 0.30 M

    Homework Statement Calculate the pH of the following solutions: (caution: these are hydrolysis reactions) a. an 0.30 M solution of NaF Homework Equations I think by hydrolysis reactions they mean that each of the given compounds is combined with $H_2O$. Then for a) NaF + HF <-->...
  40. J

    Calculate the pH of a 0.20 M solution of iodic acid (HIO3).

    Homework Statement Calculate the pH of a 0.20 M solution of iodic acid ##(HIO_3)##. ##K_a## for iodic acid is 0.17 Homework Equations ##K_a = \frac{[H^+][IO_3^-]}{[HIO_3]}## The Attempt at a Solution ##[HIO_3] = 0.20## M. The concentration of ##[H^+]## and ##[IO_3^-]## should be the same...
  41. J

    How Can I Test the pH of Foods and Drinks?

    i want to be able to test the ph of foods and drinks so I purchesed a digital ph tester for water. Is there a better ph tester option ? If I wanted to test the ph of something like mayonnaise would I just stick the tester into the mayo or would I need to mix the mayo with water first?
  42. Frankenstein19

    Calculating pKa from pH: Understanding Titration

    Homework Statement When 100.0 mL of weak acid HA was titrated with 0.09381M NaOH, 27.63mL were required to reach the equivalence point. The pH at the equivalence point was 10.99. What is the pKa of HA Homework Equations pH=pKa+log([A]/[HA] [OH]-10^(-pOH) The Attempt at a Solution...
  43. V

    [Cheese making help] Lower pH with citric acid

    I made an account to ask this. I have looked and could not understand any of the formulas I came across. I even looked for calculators, but did not understand how to use them. Milk has a pH of 6.5 to 6.7 (lets use 6.7) And I wish to lower the milk's pH to 4.9 (as an example) How do I...
  44. C

    Calculate pH of 4.41 M HCl Water Solution

    Homework Statement Hello everybody, How can I calculate pH value of 4.41 M HCl water solution? Is it possible for such a solution to exist? Thank you very much for your help, CroSinus Homework EquationsThe Attempt at a Solution When I try to find - log 4.41 I get a negative value. I do not...
  45. Dhh1994

    Can pH of a His buffer change during lyophilization?

    We lyophilized 50mg/ml mAb with PI of 7.5 in a 10mM His buffer pH 6.2. Upon reconstitution the pH is 6.5. Does anyone have an explanation for this? I am under the impression His is much less susceptible to pH change during lyophilization as opposed to something like a phosphate buffer. Thanks.
  46. H

    Solvent Extraction question at different pH levels

    The question I have been given: Draw the dominant forms of each of the compounds below and state which, if any, would be expected to extract from aqueous solution into hexane at (a) pH 12 and (b) pH 2. CH3CH2COOH CH3CH2NH2 CH3CH2CH2OH H2NCH2CH2COOH From my understanding, I can tell what the...
  47. T

    How does pH affect secondary structure of proteins?

    I understand that pH affect the tertiary structure as it will change the ionic interactions between the COO- and NH3+ groups, however, as the secondary structure is caused by hydrogen bonds, how does pH affect it? Is it because the change in tertiary structure will alter the shape of the protein...
  48. O

    Which formula to use to find the pH of a solution?

    Hello, I just had my first exam yesterday, and I'm always tripped with this question that combines neutralization with buffer solution. The task is to find the pH. I did try to understand the general concept behind it. From my understanding, if CH3COOH reacts with NAOH and the acid has a higher...
  49. ReidMerrill

    How can I prepare a 0.1M NaOAc buffer at pH 5 using titration?

    For a lab I need to create a 0.1M solution of NaOAc buffer at pH 5 It's been a while since I worked with buffers. I'm struggling to find a way to get both the proper morality and proper pH. My first though was to create a 0.2M solution of acetic acid and titrate it to pH 5 using sodium...
  50. C

    Altering pH of a luminol solution

    The recipe for luminol solution that I found on the internet is: 0.2g luminol, 4.0g Na2CO3, 24.0g NaHCO3, 0.5g (NH4)2CO3, 0.4g CuSO4 dissolved in 1 dm3 of water. How can I alter the pH of the solution to get a range of pH values from 7 to 14 without affecting the chemisty of the solution?
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