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. M

    Solving pH of Solution After NaOH Addition

    [SOLVED] pH of solution Homework Statement What is the pH of a solution in which 30.0mL of 0.010 M NaOH are added to 10.0mL of .010 M H2SO4? Homework Equations The Attempt at a Solution So first thing I did was write the equation. 2NaOH + H2SO4 ----> Na2SO4 + 2H2O I never...
  2. P

    Measuring pH probe potential and interfacing probe with uC

    I am building an automatic acid-base titrator for my senior project. I am using a Freescale s12ub microcontroller. For this project, I will need to interface a pH probe with the CMOS input on a microcontroller. The potential across the probe is supposedly proportional to pH. (-0.06 volt/pH...
  3. T

    Calculating pH of a 0.23M H2SO4 Solution

    Homework Statement Calculate the pH of a solution of a concentration of 0.23 mol/L of H2SO4, if it completely ionizes in the solution. Homework Equations [H3O] = 10^{-pH} pH = -log[H3O] The Attempt at a Solution The answer I got for this question is 0.34. I got this answer by first...
  4. H

    PH problem weak acid and weak base

    Hi I have been trying several days to solve this problem. But i can't find the procedure to solve this weak acid and weak base problem. I will really appreciate some help. What is the pH of a soft drink in which the major buffer ingredients are 6.90 g of NaH2PO4 and 5.70 g of Na2HPO4 per...
  5. H

    PH problem weak acid and weak base

    Hi I have been trying several days to solve this problem. But i can't find the procedure to solve this weak acid and weak base problem. I will really appreciate some help. What is the pH of a soft drink in which the major buffer ingredients are 6.90 g of NaH2PO4 and 5.70 g of Na2HPO4 per...
  6. D

    What should the pH of a .121M KI solution be (electrochem lab)?

    I think I calibrated my pH meter improperly during lab; I got a pH of 4.70, which doesn't make any sense, as KI isn't acidic, as far as I know. After electrolysis (2I- + 2H2O --> I2 + 2OH- + H2) with a 9V battery, I found a pH of 9.97, which doesn't seem to be correct, either: (change in...
  7. P

    Formulas from question that BATE pH calculator gave me

    Hello, I am EXTREMELY glad I found this forum. I used a chemistry calculator that was posted by a poster here in a signature (BATE calculator from ChemBuddy) and it gave me an instant result to a problem I was trying to solve for a while, and that I should have been able to do on my own. I was...
  8. Z

    Calculating Formic Acid & Sodium Formate for pH Change

    Homework Statement A solution is to be buffer at pH = 3:35 with formic acid and formate. (a) How many moles of formic acid and sodium formate are needed if the solution is to change pH by < 0:02 for the addition of 0.02 moles of strong acid? i need help how to set up a problem like...
  9. L

    How Does Rainfall Affect the pH of Unbuffered and Buffered Lakes?

    Homework Statement Im having issues with two parts of this problem, not sure what I'm doing wrong... A lake with a surface area of 12.2 acres (1 acre = 4.840 103 yd2) receives 1.67 in. of rain of pH 4.82. (Assume that the acidity of the rain is due to a strong, monoprotic acid.) How many...
  10. L

    How Do You Calculate pH Changes in a Phosphoric Acid Titration?

    Homework Statement I've been working on this problem and am having issues with some of the problems... all we learned was that EQ is pH= pka and at eq and EQ1/2 is pk1+pk2/2 which can't even be applied to this question due to x values. I would GREATLY appreciate ANY help/guidance/etc...
  11. G

    Effect of pH on enzyme activity- amylase

    Hi guys, I've got to do a project for school on the investigation of the effect of pH on the enzyme amylase. I am abit lost right now only just started A levels. Can someone suggest how i would carry out this investigation? Equipment and method would be much appreciated! And the results need to...
  12. G

    Effect of pH on AmylaseNeed help

    Hi guys, i have been set some coursework by school on the investigation of the effect of pH on the enzyme amylase. I am abit lost right now only just started A levels. Can someone suggest how i would carry out this investigation? Equipment and method would be much appreciated! And the results...
  13. H

    PH, Buffers, and Dilution question

    I understand the henderson-hasselbalch equation, and how the pH of a solution depends on the ratio of acid to its conjugate base. However, I don't understand how this concept can be related to solutions that are extremely diluted. For example, let's say you have 0.00001M acid+c.base...
  14. S

    PH effects on membrane permeability

    I had this lab done where we took beets and tested the effects of pH on membrane permeability. We used different concentrations of HCl and NaOH. Why did I get such a strong colour intensity with a test tube that had 0.001 M NaOH? And how do I know this experiment affected the protein...
  15. S

    Biology/Chemistry: pH Level and Ionizable Groups

    Homework Statement Select any molecule [from the assigned chapter] that has more than 2 ionizable groups. Write its structures, showing every atom, at pH levels 1 and 7. Homework Equations See below. The Attempt at a Solution http://en.wikipedia.org/wiki/Geranyl_pyrophosphate...
  16. N

    Calculating Titrant pH Without Henderson Hasselbach Equation

    Titrant [HNO2]= 0.10 mol/dm3 v= 25ml = 0.025 dm3 + Analyte [NaOH]= 0.125 mol/dm3 v= 20ml = 0.02 dm3 Question is: What is the ph after adding a volume 10ml of titrant? I know the answer is ph= 4,3 I'm not allowed to use Henderson Hasselbach equation. This is the...
  17. E

    PH question (volume calculation)

    I am having difficulties as to what equation to use to calculate the volume. Can someone please kindly give me some help? Homework Statement What is the volume of 6M HCl required to acidify the mixture of 1g benzaldehyde and 2mL 10M KOH to a pH ~2? Homework Equations MW of...
  18. N

    Effects of OH- Increase on Alkalinity, Acidity, and pH

    An increase in the OH- in a solution would result in an increase in alkalinity (baseness). an increase in acidity. a pH of 7. a decrease in pH. i think it would be - an increase in alkalinity, but I am not sure help!
  19. H

    Calculating Kb: Ph 0.3mol/l Weak Base, 10.66

    The Ph of 0.3mol/l of a weak base is 10.66, calculate kb. I was thinking of using ph and calculate the concentration of H ions and then calculate poh and OH, but don't know what to do next. Any ideas?
  20. F

    Chemistry pH Problem 0.02 moles HOAc

    Homework Statement A solution was prepared by dissolving 0.02 moles of acetic acid (HOAc; pKa = 4.8) in water to give 1 liter of solution. a) What is the pH? b) 0.008 moles of concentrated sodium hydroxide (NaOH) was then added to this solution. What is the new pH? (In this problem, you may...
  21. B

    Solve pH & pKb Problems - Get Answers Now!

    HELP! I just need the steps to figured out these 3 problem. I have the answes but I can't seem to figure out how to do it and my notes aren't helping. thanks! Determine the pH of a solution obtained by titrating 25.00 mL of a 0.107 M solution of a weak base using 75.25 mL of 0.100 M HCl(...
  22. L

    Calculate pH of Buffer Solution After HCl Added

    Question A buffer solution is prepared by mixing 600.0 ml of 0.600 M HClO and 400.0 ml of 1.00 M NaClO. Calculate the pH of the solution after 40.0 ml of 3.00 M HCl is added to the buffer. For HClO, Ka = 3.0 X 10^-8. Work so Far A buffer solution os prepared by mixing 600.0 ml of 0.600 M...
  23. L

    Calculate the pH of Buffer Solution with Ka=1.34x10^-5

    Question A buffer solution is prepared by mixing 380.0 ml of 0.250 M propionic acid, C2H5COOH, and 120.0 ml of 0.350 M sodium propionate, C2H5COONa. Calculate the pH of the prepared buffer solution. For propionic acid, Ka = 1.34 X 10^-5. Work thus far We have this C2H5COOH <-->...
  24. C

    What Happens to pH When H3PO4 is Mixed with NaOH?

    Homework Statement What is the pH of the resulting solution when 100.0 mL of 0.10 M H3PO4 is mixed with 200.0 mL of 0.15 M NaOH? Homework Equations Henderson-Hasselbalch, equilibrium constant expressions The Attempt at a Solution I've thought about this question for over an...
  25. L

    Calculate pH of Citric Acid at Various Concentrations

    Hello, i would really appreciate it if someone could help me with this problem. I would like to know the pH of citric acid at various concentrations. 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%. From what i have read it has something to do with its pKa value which for citric acid is...
  26. M

    Solve a Simple pH Problem: HCl + NaOH → H2O + NaCl

    I'm trying to do this homework problem, and I really am confused about how to do it. I'm familiar with dissociation of weak acids/bases, but I'm pretty confused with this problem(with a strong base and strong acid). The problem is: "40.0ml of 0.20M HCl is mixed with 40.5ml of 0.20M NaOH. a)...
  27. D

    Calculating pH After Adding NaOH to NaC3H5O2 Solution

    Homework Statement This question refers to a previous question in my book: Calculate the pH of .1 M NaC3H5O2. The question I'm stuck with now: Calculate the pH after .02 mol NaOH is added to 1 L of the *previous* solution. Homework Equations The Henderson-Hasselbalch equation or the simple...
  28. P

    Calculating pH of Buffer Solution with HCl Addition

    Homework Statement A buffer solution was formed by mixing 30ml of 0.1M sodium acetate and 15ml of 0.1M HCl a) Calculate the pH of this buffer solution. b) Calculate the pH of this buffer solution after the addition of 15ml of 0.1M HCl. Homework Equations pH = pKa + log[salt]/[acid]...
  29. E

    Why Use a Weak Base to Neutralize a Strong Acid?

    Question: TRIS is a weak base. Compute pH of a solution containing .050 moles of TRIS and .020 moles of HCl in a total volume of 2L. pKb for TRIS is 5.92. Use RNH2 to represent TRIS. Equation: pH = pKa+ log ([conjugate base]/[acid]) Work: change equation for pOH: pH = 14-pOH pOH =...
  30. P

    Calculating pH of Mixed Solutions: HCl and Sodium Acetate, Acetic Acid and NaOH

    Homework Statement Calculate the final pH of the following solutions: a) 65.0 ml of 0.105 M HCl and 100 ml of 0.118 M sodium acetate solutions are mixed. b) 100 ml of a 0.109 M acetic acid and 100 ml of a 0.123 ml NaOH solution are mixed. Homework Equations pH = pKa = log...
  31. A

    Calculate pH of 23.0 mL of 6.29 M HCl Added to 160.0 mL Distilled Water

    Homework Statement Calculate the pH of the solution a) 23.0 ml of 6.29 M HCl is added to 160.0 ml of distilled water Homework Equations pH = -log [H] Kw= [H][OH] Kw = 1 x 10^-14 The Attempt at a Solution For part a) I found the no.of moles Of HCl as 0.14467mol and from...
  32. M

    Effect of pH on beetroot cell membrane permeability

    im meant to design an experiment (at AS level) and perform it to see how the pH can affect beetroot cell membrane permeability. i don't know where to start. anyone have any experiments?? thanks :biggrin:
  33. P

    Measuring pH of Aqueous Solutions Containing NaOH

    In the textbook it stated "In aqeous solutions, the concentration of hydronium ions is always related to the concentration of hyroxide ions. Therefore we can still measure or calculate the pH of solutions of bases like NaOH, even though they are not acidic." The book also stated that pH is a...
  34. N

    PH of a mixed solution: is this right?

    Homework Statement What is the final pH of a solution obtained by mixing 200 ml of 0.400 M NH3 with 300 ml of 0.100 M HCl? (Kb = 1.8 x 10^-5) Homework Equations The Attempt at a Solution I used an ICE table and came up with 9.68. Is that correct? Should I have used two ICE tables instead...
  35. J

    Calculate the pH of 100mL HOAc + 100mL Ba(OH)2

    Homework Statement find the pH of: 100mL x .20M HOAc + 100mL x.10M Ba(OH)2 The Attempt at a Solution 100x.2 = 20mmol HOAc 100x.1 = 10mmol Ba(OH)2 20-10=10 10/200=.05M pOH = -log(.05) = 1.3 pH=14-1.3=12.7 Is this correct?
  36. F

    Predict pH of KBr solution (aq)

    Homework Statement Predict whether an aqueous solution of KBr will be acidic, basic, or neutral. Homework Equations KBr(s) → K+(aq) + Br-(aq) Br-(aq) + H2O(l) ← HBr(aq) + H3O+(aq) The Attempt at a Solution The solution will be neutral. I know that this is the correct answer. I just...
  37. R

    Buffer Solution pH: Impact of Adding 1L of 5pH on a 100L Solution

    what will be the new pH of a 100 lt solution if 1 lt buffer solution of 5 pH is added to it
  38. N

    PH question, I really don't get this

    Homework Statement What is the [H3O+] of acid rain with a pH of 4.23? Homework Equations pH = -log[H30+] pOH = -log[OH-] pH + pOH = 14 The Attempt at a Solution the four possible choices are a. 1.7 x 10^-10 b. 5.8 x 10^-5 c. 2.3 x 10^-4 d. 1.7 x 10^5
  39. L

    Soil pH affected by soil texture?

    How is soil pH affected by soil texture? any sites would be helpful alot.
  40. Y

    Calculating Hydrogen Ion Concentration & PH by Yonderboy98

    I know what the formal definition of ph is, and I am comfortable with logarithms, anti-logs, and the laws of exponents. Still, I get confused doing actual calculations and would greatly appreciate your input on the following: Suppose something has a ph of 3.5-How do you calculate the hydrogen...
  41. S

    Explaining Resistance in pH of Buffer: Strong vs Weak Acids

    could the equation - pH=pKa+log([A]/[HA]) - be applied for the case of strong acid? Although the percentage of dissociation of strong acid/base is very high, there still exists a equilibrium, right? secondly, if i tried to explain the resistance in pH of buffer *in terms of* the above...
  42. A

    Bio/chem relation between pH and [H+]

    Hi my question is How does the pH relate to the concentration of Hydrogen ions? what I think is The relationship between the pH and the concentration of Hydrogen ions is that the -log of the hydrogen ion concentration is equal to the pH, but this doesn't seem right at all. can someone...
  43. F

    Understanding pH and Buffer Solutions: Acid-Salt Ratio and pKa vs. pH and pKb

    This is not a homework question, so I cannot give exact values or anything, sorry. If we have to make a buffer solution, and we know the pH and the pKa of the acid we are going to use, would it be true to say that if the pH < pKa, we will need more of the weak acid than salt? If pH > pKa, we...
  44. F

    Calculating pH of Na3PO4 (45.0g/L): Find the Basicity

    We have 45.0g of Na3PO4 per liter. We know it is very basic but need the pH. I don't have the answers to all exercises, so if you could check my work, that'd be great. So, we have g, but moles would be more useful. So 45g x (1 mol/163.937) = 2.7 x 10^-1 mol. We know that strong bases...
  45. A

    Calculating pH of 0.001 M NaCl

    How do you calculate the pH of 0.001 M NaCl? I was thinking of doing NaCl + H2O ---> HCl + NaOH but I don't know where to go from there if that's even the right step.
  46. T

    Can Hydroclauric Acid and Water Create a pH Greater than 7? Find Out Now!

    I want to ask that there is any situation that the solution of Hydroclauric acid and water can make the pH of this solution gretater than 7.
  47. K

    PH & Concentration Help - Problem Solving

    Hi, I need some help with a few problems. Thanks! (1) You have a pH Electrode that reports a voltage in mV, which is proportional to the hydrogen ion concentration in solution. You also have pH buffers at known pH of say 4, 7 and 10. What do you do to translate the mV reading into pH...
  48. M

    Amphoteric compounds-effect of pH

    Hello friends! I have a query for which i have been trying to find an answer for a long time but in vain! Can anybody tell me how do we find the effect of pH on amphoteric compounds?I am currently working on Amphotericin B which happens to have both the acidic and the amino groups. I need...
  49. Hootenanny

    An Introduction to pH and Buffer Solutions Calculations

    An Introduction to pH and Buffer Solutions Calculations [work in progress] This is a work in progress 1. pH and Strong Acids pH is defined as the negative logarithm of the hydrogen ion concentration in a solution; pH = - log10[H+(aq)]. (From this point forward 'log' will represent log to the...
  50. T

    How Do You Calculate the Required Amounts for Buffer Solutions?

    Hey I have been having a lot of trouble in solving these problems and I have exams soon and I really don't know where to start, I know u aint meant to give the answers so instead would someone please go through all of the steps to finish this! I really need some kinda help, This question was in...
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