What is Ph: Definition and 520 Discussions

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

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  4. FlyingWhale

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

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  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

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  7. irumi

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

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  8. StarChem

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  9. marcelo

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    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

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  11. Justinboln

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  12. B

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

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  13. Boltzman Oscillation

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  14. P

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

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  15. G

    Calculate the HCl concentration in H2O from the conductivity

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  16. BillTre

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  17. Kaushik

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

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  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?

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  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)

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  23. M

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  24. D

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  25. S

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  26. D

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  27. J

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  28. J

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  29. S

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  30. ChristinaMaria

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

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  31. M

    Disolving NaCl in deionized water gives high pH value

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  32. L

    Calculating pH with and without ionic strength

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  33. Krushnaraj Pandya

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  34. Krushnaraj Pandya

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  35. opus

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  36. D

    How a pH Probe Works: A Comprehensive Guide

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  37. J

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  38. chemisthypnos

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  39. J

    Calculate pH of NaF Solutions | 0.30 M

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  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

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  42. Frankenstein19

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    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

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  44. C

    Calculate pH of 4.41 M HCl Water Solution

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  45. Dhh1994

    Can pH of a His buffer change during lyophilization?

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  46. H

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  47. T

    How does pH affect secondary structure of proteins?

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  48. O

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  49. ReidMerrill

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  50. C

    Altering pH of a luminol solution

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