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. M

    How to convert electrical conductivity to pH

    Homework Statement I have some data from measuring EC in solutions and I don't know how to convert EC to pH Homework EquationsThe Attempt at a Solution I use Arduino for programing. Values of ADC of EC that I collect from microcontroller are 80 ( for EC : 0.2mS/cm ) , 90 ( for EC ...
  2. Garlic

    Best pH Meter to Buy: 20-40 Bucks

    Hello everyone, In a few weeks I am going to have my anorganic chemistry laboratory experiments, and I want to buy one PH-Meter. I'm looking for a model that is realible but not expensive (in the order of 20-40 bucks) I'll be happy to hear your suggestions Thanks :smile:
  3. B

    Mechanism behind solution color change due to pH change

    I would like to ask for somebody to point me in the right direction - any literature I could read - regarding the mechanism behind color changes that an organic solution undergoes due to changes in pH. I am not referring to organic indicators or dyes, specifically. I have observed in my...
  4. CheesyPeeps

    PH of Water at Various Temperatures

    Homework Statement If the text is too small, it reads: 'A student measured the pH of water at various temperatures using a pH meter and obtained the following results: (table showing pH decreasing as temperature increases) The student was unsure whether the results were accurate or if the pH...
  5. fsonnichsen

    Reference Probes in pH and other electrochemical measurements

    I am amused by how skillfully most of the texts I have avoid discussing reference electrodes in electro-chemical measurement-They simply start out by discussing the H2 and Calomel electrodes with no further explanation. Both have certain hazards and seem overly complicated. So--why are these...
  6. B

    Predicting charge of organic compound at certain pH

    Which property of compounds, organic ones in particular, can help us predict their charge(s) at a specific pH? Is pKa/pKb the only one? I would like some confirmation on this. Thank you very much!
  7. S

    Raising pH of coffee/tea safely and permanently?

    Hi! I don't know much about chemistry but was hoping that some of you guys could help me with a quick question. I build wooden model ships of sail as a hobby. One "trick" for giving sails and rope an aged look is to dip them in coffee or tea and let the tannin dye the materials. The problem...
  8. B

    Help please with this precipitation exercise

    Knowing Ks=6⋅10−38 for Fe(OH)3 in neutral solutions, calculate the minimum pH of an acidic solution in order to completely dissolve 10 mg of Fe(OH)3. Data: Volume = 0.1 L. I set out the equation for the equilibrium constant. having first calculated the concentration or iron ions (9.35899*10-4...
  9. A

    Solving a pH Change After Adding Sulfuric Acid to Sodium Hydroxide

    Homework Statement A 50.0 mL aqueous solution of sodium hydroxide has a pH of 12.50. If 36.00 ml of 0.0200 mol/L sulfuric acid is added to this sodium hydroxide solution, what will be the new pH of the resulting solution? Assume that the temperature stays constant at 25C, and that the volumes...
  10. R

    Checking pH meter calibration HCL >37%

    Hi, I've calibrated our pH meter using 4.01 and 7.01 buffer solution, but I'm not sure if the probe has dried out at some point. So I want to check the calibration, I have some HCl > 37% that I can use. Just a quick question, since pH is on a log scale so I have to make solutions every ten...
  11. donaldparida

    What is difference between pH and pKa , pOH and pKb?

    Do pH and pKa refer to the same concept? The same question for pOH and pKb also. What does kWh actually mean. In have read that it is the ionic product and is the product of [H+] and [OH-] but what does it indicate. Does it have any full form?
  12. R

    Solubility of tartaric acid/sodium tartrate in high vs low pH

    Homework Statement So we did a lab in organic chemistry where we did a resolution experiment for enantiomers and in the separatory funnel we had sodium tartrate/tartaric acid left in the aqueous phase of the funnel. It asks why this compound is more soluble in high ph solutions as compared to...
  13. A

    Two pH questions i don't understand

    Homework Statement 1) Which solution has the higher pH, a 0.001 M solution of NaOH or a 0.001 M solution of Ba(OH)2? 2) Would a 1.0 × 10-8M solution of HCl have pH < 7, pH = 7, or pH > 7? My professor said she shouldn't have put HCl as the solution, but that it doesn't matter apparently...
  14. Natsu1993

    How to prepare 50mM Na2HPO4/H3PO4 buffer, pH 4.5

    The have to prepare the buffer but I really don't know how. Is the any formula for the buffer preparation? Ps. Sorry but one more thing, what does the "/" between Na2HPO4 and H3PO4 mean?
  15. ReidMerrill

    Phosphate Buffer and pH: Would it be Effective at pH 8.5? - Homework Discussion

    Homework Statement Phosphate, present to an extent of 0.01 M, is one of the main buffers in blood plasma, whose pH is 7.45. Would phosphate be as useful if the plasma pH were 8.5? Homework Equations pH = pKa+log[A/HA] Ka1 = 7.11x10^-3 pka1= 2.148 Ka2=6.34x10^-8 pka2= 7.198 Ka3 = 4.22x10^-13...
  16. Bayoudh101

    Why does the pKA of -COOH change when -NH3+ is present in the same molecule?

    Its a very simple question . So when the carboxylic acid radical -COOH is standalone in an aliphatic molecule without any other acid or basic radicals Pka would be around 4.5 . But when something like -NH3+ is present in the same molecule the Pka for -COOH changes , even though -NH3+ wouldn't...
  17. A

    How to make 0.2 M Tris-Acetate Buffer pH 6

    Hello, I need to make a 0.2 M Tris-Acetate Buffer pH 6 and I can't find a protocol for this specific buffer. I know that I can make a Tris solution (i.e. 12.11 g of tris(hydroxymethyl)aminomethane in water), adjust the pH to 8 and dilute to 1000 mL with water. Is the same true for pH 6...
  18. fsonnichsen

    Accurate measurement of pH - best methods

    I am "proofing" various pH probes in an in-situ fresh water environment--this is a low electrolyte environment where such probes typically do not perform very well. I want to routinely sample the water and obtain accurate pH data for comparison. Can someone enlighten me on the what modern (non...
  19. usED

    Determining pH Fluctuations at Maximum Dosage of 50mg/L of 93% Sulphuric Acid

    Homework Statement pH fluctuations need to be determined at a maximum dosage of 50mg/L of 93% sulphuric acid . Homework Equations If the start pH of the water sample is 8, how much will pH be lowered by adding of 50mg/L of 93% sulphuric acid, and what is the correlation between the different...
  20. R

    I am sure I am doing this Acid/Base problem wrong

    What is the pH of a solution made from 34.6 ml if 3.45*10^-4 M of H2SO4 added to 41.7 ml of 4.56*10^-4 M of Al(OH)3? I know how to find H+ and OH- and pH I also know how to use x mol / L, but I cannot get them to click together. Everyone keeps telling me to use RICE but my professor never...
  21. T

    What is the pH of this new solution?

    Homework Statement Equal volumes of two solutions of hydrochloric acid are mixed. One solution has a pH 1 while the other pH 5. The pH of the solution obtained is? A) Less than 1 B) Between 1 and 2 C) 3 D) Between 4 and 5 E) More than 5 Homework Equations -log[H+] = pH 10-pH = [H+] The...
  22. D

    Find ph based on given volume and molarity of HCl and NaOH

    Hello! I am trying to crack the following problem: What is the pH of a solution formed by mixing 125.0 mL of 0.0250 M HCl with 75.0 mL of 0.0500 M NaOH? Here is how I am approaching the issue: both HCl and NaOH are strong acid and base respectively. Hence the concentration of [H3O+] =...
  23. E

    A Methods for finding properties of quantum dots?

    What are some good methods to determine properties such as light quality/intensity, pH, and water solubility of quantum dots? Other properties are welcome, as well. I do not have a college lab available, so some equipment may not be possible to get. This is for my science fair project next year...
  24. Justin LaRose

    How Can Ammonia Be Used to Adjust the pH of a Highly Acidic Solution?

    Homework Statement [/B] I work in a lab, normally we evaporate our acid and dilute with water, but I have 300 samples and this would destroy the fume hood so I need to raise the pH using ammonia. known data: Samples are 40ml of 9M HCl I need to add Xml of XM ammonium hydroxide (aka aqueous...
  25. N

    Calculating the molar concentration of H3O+ and pH of solutions

    Homework Statement Calculate the the molar concentration of H3O+ ions and the pH of the following solutions: a) 25.0 cm3 of 0.144 M HCl(aq) was added to 25.0 cm3 of 0.125 M NaOH(aq) b) 25.0 cm3 of 0.15 M HCl(aq) was added to 35.0 cm3 of 0.15 M KOH(aq) c) 21.2 cm3 of 0.22 M HNO3(aq) was added to...
  26. coolsalena

    I How does pH affect crystal growth?

    Hi! The crystal that I am growing is Mohr's salt. though i have already optimized the parameters (pH), i would like to know the reason why pH affects it's growth. pH 1: no crystals formed pH 2: crystals formed Thanks!
  27. NihalRi

    How to Calculate pH from pKw: Solution for Water at 10°C

    Homework Statement pKw for water at 10 deg Celsius is 14.54. What is the pH of pure water at this temperature? Homework Equations kHw = [H+][OH-] The Attempt at a Solution I don't even know where to start on this one
  28. B

    How do I lower the pH of a water supply

    Homework Statement [/B] Just a general question to see if I'm doing this right. The volume just doesn't seem right. Anyways we have a water supply of 1.6 million gallons with a pH of 9.93. We want to get the water to a pH of 6 using a 30% HCl solution.Homework Equations M1V1+M2V2=M3V3...
  29. RoboNerd

    Titration error affecting the PH of the endpoint

    Homework Statement Hi everyone. 1) If I perform a titration with a buret not rinsed in the titrant, then how will the pH of the endpoint be affected? 2) Also, if the volumetric pipet used to measure the analyte is not rinsed with the analyte, how will that affect the pH of the endpoint...
  30. I

    Ph diagram for a vapour compression cycle

    Homework Statement Homework Equations N/A The Attempt at a Solution I am trying to understand the above ph diagram (for a vapour compression cycle), In some examples, point 1 is situated as above in the image (i.e. to the right of the saturated vapour line) and at other times it's situated...
  31. I

    Interpreting enthelpy on a ph diagram

    Homework Statement 2. Homework Equations q = w+Δh The Attempt at a Solution I fail to understand how they obtained the 3 equations at the bottom. For the first one I understand that q = Δh since w = 0 but why is it h1-h4 rather than the other way around? Also, why does this h1-h4 equal...
  32. terryds

    Calculating pH of Al2(SO4)3 Solution

    Homework Statement 6.84 gram aluminium sulfate (Al2(SO4)3) is added into water so the volume of the solution becomes 2 liters. If we know that the atomic mass Al = 27, S = 32, and O = 16, determine the pH of the solution! (Kb Al(OH)3 = 5*10^-9) Homework Equations ##[H+] =...
  33. S

    PH Tester for Solids: Buy, Price & Info

    Hello everyone, First of all thank you for your help. I'd like to know if there are any ph testers for solids not diluted and where can I buy them and how much would they cost. Thanks!
  34. terryds

    Acid Mixture pH Problem: Calculating Solution pH with CH3COOH, CH3COONa, and HCl

    Homework Statement 30 mL CH3COOH 0.2 M is mixed with 60 ml CH3COONa 0.1 M and then added with 10 mL HCl 0.1 M, then what is the pH of the solution ? (Ka = 10-5) A. 3 B. 5 - log 1.4 C. 5 - log 2 D. 4 - log 1.4 E. 5 + log 2 Homework Equations [H+] = Ka * [HX] / [X- ] ---- buffer [H+] =...
  35. A

    Problem measuring PH (it oscilates) for gastric juice

    I bought a PH meter with glass electrode. I calibrated it using a buffer solution following the instructions. When I measure the PH of tap water, vinegar, or other simple liquids it initially keeps changing but eventually it stabilizes at the correct value. But I tried to measure gastric juice...
  36. RoboNerd

    Question about acid and base indicators

    Homework Statement Methyl red has the following structure [not listed here on this post] Ka = 5.0 * 10 E -5 It undergoes a color change from red to yellow as a solution gets more basic. Calculate an approximate pH range for which the methyl red is useful. What is the color change and the...
  37. S

    Solubility in g/L of zinc hydroxide with pH of 8

    Homework Statement Zinc hydroxide has the chemical formula of Zn(OH)2. It has a very low solubility. What is the solubility in g/L of Zinc Hydroxide in a solution with a pH of 8? Homework Equations zinc hydroxide formula 14-pH = pOH[/B]The Attempt at a Solution 10^-6 (the pOH) gives me the...
  38. B

    What is the relationship between titrations and starting pH?

    Homework Statement What was the concentration of acid S before the titration? Homework Equations MaVa=MbVb The Attempt at a Solution So for this problem, the solution manual suggests that we use the formula above to solve for the pH of acid S before the titration. But why do we use the...
  39. Stephanus

    Understanding ORP in Water with NaCl

    Dear PF Forum, I would like to thank this forum for providing me invaluable helps lately. I'd like to understand ORP in water. I'm aware that PF discourages member for not doing research first. I've (been) reading redox, antioxidant, pH, covalent, including...
  40. Stephanus

    Understanding pH - FAQs for the PF Forum

    Dear PF Forum, Actually I want to study how antioxidant can benefit for our health. But, my understanding in chemistry is very limited. Perhaps I have to go back and study pH, first. I have read many sources in the internet. And this is one of them...
  41. F

    Why does alanine salt have a pH of 6.113?

    I understand that alanine salt ooks like this: However, does it look like that in solution? Does the salt dissociate? I know that alanine salt has a pH of about 6.113 because it is the average of the 2 pKas. However, if this salt dissociates, it seems that the carboxyl group is a weak base...
  42. L

    Glass electrode voltage calibration and pH analysis.

    Hi, I'm stuck on part b) of the question below: Q: In order to perform pH determinations with a glass electrode, the cell potential was measured for threestandard solutions with the following pH values at 25 C: 2.04, 7.05, and 9.20. The cell voltage readout(in mV) for each of the above solutions...
  43. U

    Controlling pH of solution without changing its conductivity

    Hi, I need to conduct experiments at fixed pH. The complication is that the solution I'm using will have NaCl in it. So if I add HCl or NaOH to make the solution more acidic or basic, the conductivity of the solution (as measured by a conductivity meter) will change due to the added Na+ or Cl-...
  44. terryds

    PH of Mixed Solution with 0.1M KOH and 0.1M HNO2

    Homework Statement 500 mL KOH solution (0.1 M) is mixed with 500 mL HNO2 (0.1 M) so that the reaction becomes: ##KOH + HNO_2 \rightarrow KNO_2+H_2O## If Ka of HNO2 is ##5 \times 10^{-4}##, determine the pH of the solution 2. The attempt at a solution ##KOH + HNO_2 \rightarrow KNO_2+H_2O##...
  45. P

    Measuring pH on metallic planar surface

    We are currently trying to measure pH levels on the (wet) surface of metals as part of a study about corrosion. The surface may have a non-conductive protective layer. - is it feasible to measure pH on a planar surface (dry or wet)? Which kind of sensor probe can be used for this task? -...
  46. V

    Determining pH using Henderson-Hasselbach equation?

    Homework Statement Determine the pH of the solution (to 2 decimal points) after the addition of 50.0 mL of 2.5 M nitric acid (HNO3) to 500 mL of 0.500 M BIS−TRIS propane (C11H26N2O6), a weak base). Assume that the 5% approximation is valid and that the volumes are additive. The pKa of BIS−TRIS...
  47. TheSodesa

    What is the pH of a 6.0×10^-4 M NaNO2 Solution?

    Homework Statement It's all in the title. Correct answer: pH = 7,20. K_a (HNO_2) = 4,0 \cdot 10^{-4} Homework Equations K_b = \dfrac{K_w}{K_a} K_b = \dfrac{HB^+ \cdot OH^-}{B} The Attempt at a Solution NaNO2 fully dissolves in water giving 6,0 \cdot 10^{-4} M \, NO2^-. Now water forms an...
  48. K

    How do I find the ph without using Hasselbach's equation?

    Homework Statement hi so in my lab class we made a buffer solution by mixing 20.00 ml of 0.100 M Sodium Hydroxide and 40.00 ml of 0.100 M of acetic acid. We then poured 15ml of this buffer solution into a beaker. So we essentially have 15 ml of this buffer solution in the beaker. We then added...
  49. A

    How Do You Calculate pH and [OH-] for a Mixed NH3 and NH4Cl Solution?

    Homework Statement [/B] NH3(aq) is a weak base with Kb = 1.8*10-5, Calculate [OH-] in a solution that is made by mixing togeather 500ml of 0.20M NH3(aq) and 500ml of 0.20M NH4CL(aq), what is the value of Ph?Homework Equations Henderson Hasselbalch: ph = Pka + log([conj.base/acid]) As well as...
  50. Eclair_de_XII

    How do you calculate the pH of 35.0-mL of 0.15M acetic acid?

    Homework Statement "A 35.0-mL sample of 0.150 M acetic acid (CH3COOH) os titrated with 0.150 M NaOH solution. Calculate the pH after the following volumes of base have been added: (a) 0 mL, (b) 17.5 mL, (c) 34.5 mL, (d) 35.0 mL, (f) 50.0 mL." Homework Equations Ka = [H+][A-]/[HA] Ka = 1.8 ⋅...
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