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.

View More On Wikipedia.org
Recent contents Top users
  1. P

    How Is pH Calculated for a More Alkaline Solution?

    Question is: An unknown solution is 40 times more alkaline than neutral water which has a PH of 7. Determine the PH of the unknown solution. Here is what I have: 40 = (log base 10 x)/(log base 10 7) 40 = 10^(x-7) 10^1.4 = 10^(x-7) 1.4 = x - 7 x = 8.4 The answer is supposed to be...
  2. A

    Finding pH Values for Acids and Bases Without Experiments

    I have to place two acids and two bases from a previous assignment on a pH scale using the information I acquired during that particular experiment. The problem is, I couldn't get all the materials I needed so I didn't get to do the assignment. I've been able to figure out what vinegar's pH is...
  3. U

    Solve pH of Solution with 0.1M Ammonia & 0.141M Ammonium Chloride

    What is the pH of a solution 0.1 M in ammonia and 0.141 M in ammonium chloride? (Kb for ammonia is 1.8e-5) i would really appreciate if someone can pt me in the right direction on how to solve this qn
  4. S

    PH calculation of the solution

    This problem is driving me nuts. :-p The polyprotic acid, H2SO4 has a complete disassociation at the first step and its pKa for the second step is 1.9. When CaSO4 dissolves ina strong acidic solution of HCl, the final concentration of Ca2+ is 0.03 M and [SO42-] is 0.008 M. What is the pH of...
  5. Pengwuino

    Help Needed: Balancing pH of Acetic Acid & NaOH Mixture

    I have a question here and i don't really know how to do it. I need to know : What is the pH of a mixture of 30ml 0.1M acetic acid and 30ml of 0.1M NaOH? \[HC_2 H_3 O_3 = 1.8*10^{ - 5} \] I'm not even sure what the equilibrium equation would be! Any help would be appreciated.
  6. D

    Solving for pH with diprotic/triprotic acids

    i know if you have an acid, say .0001 M HCl, to get the pH you simply take the -log of the acid concentration (which is the same as [H+]), but what if you have a diprotic (H2SO4) or triprotic (H3PO4) acid...do you need to multiply the acid contentration by 2 or 3 to get the new H+ concentration...
  7. C

    What Is the Correct pH of a 0.15-M NaX Solution?

    K(a) for HX is 7.5 x 10^-12. What is the pH of a 0.15-M aqueous solution of NaX? a. 7.87 b. 1.85 c. 5.97 d. 8.03 e. 12.15 HX --> H+ + X- I found H+ concentration, which is 1.06 X 10-6, then found pH of this, and it is 5.97. I wasn't sure where to go from here so I guessed...
  8. S

    Which Salt Produces Lowest pH Solution?

    Which one of the following salts, when dissolved in water, produces the solution with the lowest pH? a.NaCl b.NH4Cl c.MgCl2 d.AlCl3 Ammonium chloride My answer lies with b or d since they are both acidic salts, but I think is it d since the K_a is greater...
  9. M

    What is the pH of hydroxylamine?

    What is the pH of hydroxylamine? From my calculations, it is 6.04. But it is a base. So why is it less than 7?! For calculations I just used the Henderson-Hasselbalch equation. The Kb is 1.10*10^-8, and when 0 ml of titrant has been added, the pH would be 6.04.
  10. Pengwuino

    Experiment's ph, simple i think

    In an experiment we did, we simply added 5ml of 0.1ml HCl into 20ml of a .5M solution of an unknown weak base. I'm not sure how we calculate the equilibrium constant though We know the pH is 5.855 which means the pOH is 10^-(14-5.855) = 7.161 x 10^-9. Now I'm a bit confused. Is the [HB+]...
  11. T

    How Does pH Change During Electrolysis?

    Hey all. It has been a while. I have been interested in electrolysis for a while now and have been learning how different factors affect the reaction, e.g. distance of electrodes, concentration of solution, volume of solution electrolysed etc. However I am having problems finding research...
  12. S

    Calculating pH of Ca(H2PO4)2 in H20: Tips & Steps

    What is the pH of 340 mg of Ca(H2PO4)2 in 600 mL H20? Well, find M of Ca(H2PO4)2 by converting mg -> g -> mol and M = mol Ca(H2PO4)2/.6 L Is Ca(H2PO4)2 a buffer? I don't know what to do. Do you do an equation of Ca(H2PO4)2 --> Ca (2+) + H2PO4 (-). What steps must I follow? Thank you...
  13. H

    PH of solution (not enough infromation?)

    Both are confusing me. I don't know what information to use (K values) I'd really appreciate some help! Calculate the concentration of all species present in a 0.25M solution of ethylammonium chloride (C2H5NH3CL) (Not sure you if you may need this, but C2H5NH2 has a Kb value of...
  14. S

    PH and the Acid Dissociation Constant

    1. What is the hydronium ion concentration and the pH for an aqueous solution of NH3 that has a hydroxide ion concentration of 2.25E-3 M? a. 4.44 x 10-11 M, 3.65 b. 4.44 x 10-11 M, 10.35 c. 4.44 x 10-12 M, 2.65 d. 4.44 x 10-12 M, 11.35 [OH] = 2.25E-3 pOH = -log(2.25E-3) = 2.6478...
  15. Math Is Hard

    Questions from a lab on pH and water

    ok, sorry. Couple of dumb questions..:redface: We had a lab last night, and one part involved testing the pH of various substances (we used the little strips of litmus paper and measured the color against a chart). My group tested pure water and we obtained a pH measurement of 7. Another...
  16. F

    Determining pH of Solution: 2 Acid Mix with HCl and CH3COOH

    Hi, I got a problem with something regarding to chemistry. How can you determine the pH of a solution with two Acids? The question says that A 50.00 mL aqueous solution is made by mixing the following two solutions: 10.00mL 1x10^-9M HCl 50.00mL 1*10^-4 M CH3COOH (Ka= 1.8*10^-5) a)...
  17. C

    Finding the pH of NaCN Need K Value

    I'm being asked to find the pH of a 0.050 M solution of NaCN. I figured out the expression to be x^2/ 0.050 -x, now all i need is a value for k, however I'm not given that value. I know the pH depends on the molarity of the hydrogen ion at equilibrium, however to find that I need to find x...
  18. H

    PH of 50.0g Na3PO4 in 1L Very Basic

    What is the pH of a solution containing 50.0g of (Na_3)(PO_4) in a liter of solution? We are given that (Na_3)(PO_4) is very basic.
  19. N

    Acid Base Titration: Finding pH

    Hi. I am having trouble with acid-base titration excercises. 0.02 L butanoic acid @ 0.1 M is titrated with 0.01 L NaOH solution @ 0.1 M. The Ka of butanoic acid is 1.54X10^-5. Find the pH. The answer is 4.81. I know how to find the pH when no NaOH is added, but I really don't see how the...
  20. benzun_1999

    Calculating pH of Strong and Weak Acids with 10^-7 M Concentration - Explained

    Can anyone tell me how to calculate pH of an strong and weak acid with conc 10^-^7 M . Please just explain the method. i read a little about it. Why is it necessary to take into consideration the change in conc of H^+ from water? -Benzun
  21. S

    Calculating pH and Ionization of Aspirin Solutions

    Question: Aspirin is a weak acid. (a) Calculate pH of 0.2M solution of aspirin at 25 degrees celsius (Ka = 3.0 x 10^-4 at 25 degrees celcius). (b) Determine the percent ionisation (c) Explain qualitatively the effect of adding 0.01M hydrochloric acid to the aspirin solution. (d)...
  22. A

    Digestive Secretion pH: 8-9.0 Effects

    can anyone tell me what parts of the digestive secretion have high basic pHs of 8-9.0...and they gradually increase in effectiveness for certain jobs
  23. N

    Finding pH of a buffer solution

    Hi. I was wondering if someone could please explain how to do this question. Find the pH of 1 L buffer (1 mol/L CH3COOH, 1 mol/L CH3COO-) when 0.1 mL 1 mol/L HCl is added. Help would be appreciated. Thanks in advance.
  24. P

    What is the pH of NaOH & H2SO4 Mixture?

    Hi everyone i have comed across a fairly difficult question in chemisty that's been baffling me. A 51.1 mL of 0.153M NaOH was mixed with 27.5mL of 0.0147M H2SO4. What is the pH of the resulting solution. What I want to ask is shouldn't the resulting solution, water, be neutral with pH of 7...
  25. G

    Deeper Understanding of pH Scale

    I am asked to prepare some information on ph scale. I know what pH is, I know how to calculate it in some cases, I know it is lower than 7 for acid and higher then 7 for base - is there anything more important? G
  26. N

    Exploring the Importance of Buffers: Understanding pH in Grade 7 Science

    The tern "buffer" is used in many products. What is a buffer? Some weak acids and bases work as a buffer system. Biocarbonate (HCO3-) is a common ion in your blood stream which acts as a buffer. Write an equation for how the pH of blood is restored to normal range when it bocomes acidic using...
  27. J

    Measuring pH and Ka of Acids: Exploring Alternative Methods

    Hi, I've got this question where I have to describe two methods of measuring the pH of a substance. I've already got the one using electrochemical potentials, but I'm a bit stumped on the second method. What I've said is to carry out a titration with an alkali until the solution is...
  28. S

    Calculating the pH of 0.1M Acetic Acid Neutralized by NaOH (Ka = 1.7 x 10^-5)

    Hi Guys! cakculate the pH of a 0.1M acetic acid when it is half neutralized by NaOH solution (Ka= 1.7 x 10^-5) Ans: 4.7695 My dear friends! I am unable to understand the language of this question , Please tell me this question in some easier words so that i can just solve it on. A...
  29. B

    Understanding Acidity: Pka and pH

    I have a question about pka and pH say that the pka of Acetic acid is 4.7 and the ph of the solution is 3.5, that means that the solution is acidic so it wants to donate protons, would that mean that Acetic acid in this solution would be in the protonated form, that means it will not donate it...
  30. J

    Calculating the pH of Gastric Juice from a Frog

    Hi, My Question: Upon evisceration, it was discovered that the frog had died due to acid ingestion. 10mL of gastric juice was found in its stomach required 7.2mL of 0.1 M NaOh for neutralization. Calculate the pH of its gastric juice. I'm confused, how would I approach this problem...
  31. A

    PH: product of concentration of H+ and OH-

    Why is the following true?: \left[H^+\right]\left[OH^-\right]=10^{-14} It seems like they would cancel out (equal 10-7 instead). Thanks for your help.
  32. A

    Calculating pH Change from HClO4 Addition

    when you add 10.0 mL of 1.0M HClO4 into 990.0mL water, the pH changes by 2. how would you find the change in pH?
  33. D

    PH of weak acid/weak base salts

    I'm trying to show my students that CaCO_3 is basic. Ca^2^+ comes from Ca(OH)_2, which is a weak base due to it's low solubility. CO_3^2^- comes from the weak acid HCO_3^-. To compare the two we compare: 1) Ca^2^+ + H_2O --> Ca(OH)_2 + H_3O^+ and 2) CO_3^2^- + H_2O --> HCO_3^- +...
  34. P

    Ph meter or acid/base titration?

    Which would you use advising, a ph meter or acid/base titration? advantages/disadvantages to both?
  35. X

    What is the pH Level of Urea & Sweat?

    Urea? pH level of it? Does anyone know the pH level of Urea or Sweat? I can't seem to find this info anywhere, although I think both is basic since they contain ammonia.
  36. G

    Calculating Angular Speed: 70 N-m Torque on a 160kg*m^2 Disk for 10s

    A torque of 70 N-m acts for 10s on a disk with moment of inertia 160kg*m^2. If the disk is originally stationary, what's final angular speed of the disk?
  37. G

    Is the pH of the equivalence point equal to the pKa of the indicator?

    quote from http://www.chem.ubc.ca/courseware/pH/section15/content.html Intuition may suggest that the endpoint of the titration will occur at the equivalence point if we choose an indicator whose pKa is equal to the pH of the equivalence point. If such an indicator was chosen, the colour...
  38. G

    How to Calculate the pH of a 0.1M Diprotic Acid Solution?

    This pH calculation question is only for those interested, but I wan't to do it, but I have no idea where and how to start... What is pH of solution of 0.1M diprotic acid if loarithms of overall protonation constants are 4.3 and 5.5. What is going on? No idea how to start... Borek, are...
  39. J

    PH and pOH and [H+] and [OH-] Problems

    1. Two HCl(aq) solutions have pH= 2.00 and pH= 3.00, respectively. If equal volumes of these two solutions are combined, the pH of the resulting solution wil be ... Now I know the answer is 2.26 but I don't know how to actually solve it.. 2.Aniline(C6H5NH2) is a weak base. At 25C, a 0.100M...
  40. J

    Working out the ph of CH3COONa

    Hi ppl. I have a question. I'm given the pka of ethanoic acid/ethanoate ions at 4.75 and i have to work out the ph of a 5*10^-2 moldm3 solution of sodium ethanoate. I worked it out by getting the Ka from 10^-4.75 and then saying that the concentration of Ch3COO- in the dissociation of ethanoic...
  41. C

    PH - really basic, I know, but I'm tired

    pH -- really basic, I know, but I'm tired Hi Chem masters out there, Anyone want to help me with this one? What is the pH of a solution with 10 g of sodium carbonate and 10 g of sodium bicaronate dissolved in enough water to make 0.25 mL of solution?
  42. B

    Comparing pH of HBrO4 and HIO3

    Which is stronger (lower pH): {\text{HBrO}}_{\text{4}} or {\text{HIO}}_{\text{3}} ? How would I name {\text{HIO}}_{\text{4}} -- Periodic acid, I suppose? If perchoric acid is {\text{HClO}}_{\text{4}} , why then is periodic (per-iodic) acid {\text{H}}_{\text{5}}...
  43. G

    Calculating Equilibrium Concentrations of H+ and HSO3 in SO2-Rainwater Reaction

    Hi, can someone please give me a hint to this problem? The concentration of SO2 in the troposphere over a certain region is 0,16 ppm by volume. The gas dissolves in rainwater as follows: SO2(g) + H2O(l) >> H+(aq) + HSO-3(aq) Given that the equilibrium constant for the preceding reaction is...
  44. W

    PH could be dertermined by just looking at the chemical color

    I a have a broad background in chemistry so I know the basics. I was looking at a tanning product and this was the guy's big claim "All these ingredients have high pH levels of over 6! What does this mean? A pH of over 6 is the COLOR ORANGE!" Now, I wasn't aware that pH could change the color of...
  45. C

    Solving for the Safe Combination: pH of Solutions A & C

    Captain Kirk, of the Starship Enterprise, has been told by his superiors that only a chemist can be trusted with the combination to the safe containing the dilithium crystals that power the ship. The combination, which consists of four numbers, is the pH of solution A described below, followed...
  46. C

    How to Calculate pH and Molarities in Sulphuric Acid Solutions?

    Assuming the first ionization of sulphuric acid is 100% and the K_{a2} of sulphuric acid is 0.10M at 25 degree celsius.(Ka is the acid disocciation constant) a. Find the pH of a 0.1M NaHSO_4 b. Calculate the molarities of H^+, HSO_4^-, SO_4^{2-} respectively in 0.1M H_2SO_4 Here are my...
  47. T

    Chemistry: pH after adding water

    I am trying to find what the new concentration of OH^{-} in a solution of potassium hydroxide (pH = 11.65) is after diluting it with water to six times the original volume. It is at 298.15 K (25 degrees Celcius). I have found the concentration of H_{3}O^{+} and I guessed that I just multiply...
  48. P

    How can we determine the effect of pH on amylase activity?

    In the human alimentary canal, starch is broken down by amylase. The pH of the alimentary canal varies batween pH 2 and pH 8.5. My question is how we can ivestigate the effect of pH on the activity of the amylase. thank you.
  49. T

    Do pH levels carry on thorugh evaporation?

    I need to know: In a closed system sealed off from outside air, if water from a mass of basic water evaporates, will the pH of the air be affected? If so, when the air condenses, how wil the pH of soil in the closed system be affected? Thanks for the help.
  50. M

    Measuring Liquid pH: Is a Soil Meter Accurate?

    Does anyone know if it is possible use a soil pH meter to measure the pH of liquids (ie. not soil)? Or a better way to phrase it, is there any diference between a soil pH meter and a normal pH meter meant to be used on liquids that would cause inacuracies or other problems if one was...
Back
Top