In the differential design, 2 electrodes measure pH differentially with respect to a third metal ground electrode. Then the color of the litmus paper is matched with the pH scale and checked the exact value of pH between 0 to 14 on a pH scale. How to Calculate pH and [H+] The equilibrium equation yields the following formula for pH: pH = -log 10 [H +] [H +] = 10 -pH. Legal. This question is about the theoretical pH of a buffer solution. For the undiluted acid solution in beaker 1, perform a weak acid problem to calculate the pH of 0.50 M CH3COOH. However, when an approximation is made, you have no confidence in the calculated pH of 6.70. Calculate the theoretical pH of each HC,H,O, solution, using Equation 5 and the K, value given in Table 1. The concentration of hydronium ions is equal to the concentration &\ce{CH3COOH + &OH- &<=> &CH3COONa + H2O}\\ The pH value of a substance can be calculated using our online pH calculator. When calculating the concentration after dilutions, keep in mind the amount of moles is still the same, so just use the formula $\ce{M1V1 = M2V2}$. Now you know how to calculate pH using pH equations. Calculate pH using either the concentration, weight, or volume method. Solving for \(\color{ref} x\) from Equation \(\ref{2}\) gives, \[x = \dfrac{K_{\large\textrm{w}}}{y} - y\], and substituting this expression into \(\ref{1}\) results in, \[K_{\large\textrm{a}} = \dfrac{({\color{Red} x+y}) \left(\dfrac{K_{\large\textrm{w}}}{y} - y\right)}{C - \dfrac{K_{\large\textrm{w}}}{y} + y}\], \[\begin{align} For reference, it's around the timestamp. What is the pH of this solution? Try these sample problems to test your knowledge of pH. Compute pH Instructions for pH Calculator Case 1. Combination pH sensors can also be built in larger, sturdier bodies with process connections (like NPT threads) built in. The pKb of ammonia is 4.75 at 25C. Studies mathematics sciences, and Technology. Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. Connect and share knowledge within a single location that is structured and easy to search. The calculator takes pKa and concentration as input. By clicking Accept All Cookies, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts. we can take 10 to both sides. PH is defined as the negative of the base-ten logarithm of the molar concentration of hydrogen ions present in the solution. \text{C}& -0.01&-0.01&+0.01\\ The equation for the partial dissociation of a base is then the equilibrium equation for that base in solution: 1. Method 1. To determine pH, you can use this pH to H formula: \small\rm pH = -log ( [H^+]) pH = log( [H+]) A pH (little p) of 7 only means neutral water at 25C, but for other temperatures this means a pH above or below 7. There's another way to This method is illustrated below. Use Kaequation \(K_a = \dfrac{[H_{3}O^+][A^-]}{[HA]}\) and ICE table. we had two decimal places for our pH, we have the \[\begin{array}{ccccc} Petrucci,et al. 0.200-x &&x &&x\\ equal to the negative log of the concentration of hydroxide ions. Select your chemical and its concentration, and watch it do all the work for you. So, the pH is calculated for the example like this: pH=-log (0.026)= 1.6. to the negative 10th molar. What is theoretical pH, and how do I calculate it? Enter both the weight and total volume of your application above if the chemical is a solid. Since \(H_2O\) is a pure liquid, it has an activity equal to one and is ignored in the equilibrium constant expression in (Equation \ref{eq3}) like in other equilibrium constants. "ERROR: column "a" does not exist" when referencing column alias. $$, $\mathrm{pH} = 4.74 + \log (0.06/0.04) = 4.926$, Although in our experiments the actual pH was 4.17 after $\pu{10mL}$ of $\ce{HCl}$ was added and the pH after 10 mL of NaOH was 4.98, $\ce{[NaOH]} = \pu{0.2M}$ and $V = \pu{10mL}/\pu{0.01L}$ thus $n= 0.002$, $$ International Union of Pure and Applied Chemistry (1993). pH Calculator The most accurate way to determine pH is through use of a calibrated pH meter and electrode. \ce{[A- ]} &= x\\ sign over to the left side. The pH scale runs from 0 to 14a value of seven is considered neutral, less than seven acidic, and greater than seven basic. Worked examples: Calculating [HO] and pH. moles HAc = 0.01 + 0.002 = 0.012 Calculate a theoretical pH for the solution in beaker 6 by performing a weak base problem to calculate the pH of 0.50 M NaC2H3O2. hydroxide ions is equal to Kw, which is equal to 1.0 times In pure water, the concentration of hydronium ions equals that of hydroxide ions. I know I pretty much just wrote a wall of text, but hopefully that helps nonetheless. The carbonate ion is the Conjugate base of the weak acid $\ce{HCO_3^-}\ (K={4.7\times10^{-11}})$, so this solution will alkaline. It only takes a minute to sign up. Pure water is a neutral substance which means the concentration of hydronium ions x, then the concentration of hydroxide ions would also have to be x 3. Covington, A. K.; Bates, R. G.; Durst, R. A. Math and Technology have done their part, and now it's the time for us to get benefits. Retrieved from https://www.thoughtco.com/how-to-calculate-ph-quick-review-606089. Also, you can enter the name of the substance like HCl in the case of hydrochloric acid solution.if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[250,250],'calculatores_com-box-4','ezslot_4',116,'0','0'])};__ez_fad_position('div-gpt-ad-calculatores_com-box-4-0'); Theoretically, the pH value for acids is calculated by using the molarity of the solution and the number of free H+ ions released in the solution. To learn more, see our tips on writing great answers. First, you're going to want to look out for a reaction. You can calculate the pH of a chemical solution, or how acidic or basic it is, using the pH formula: pH = -log 10 [H 3 O + ]. Here you would use a simple formula to calculate the pH value manually. at 25 degrees Celsius. &= 2.24\times 10^{-7}\\ The pH of an aqueous solution is based on the pH scale which typically ranges from 0 to 14 in water (although as discussed below this is not an a formal rule). Just follow below steps:if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[250,250],'calculatores_com-large-leaderboard-2','ezslot_6',128,'0','0'])};__ez_fad_position('div-gpt-ad-calculatores_com-large-leaderboard-2-0'); Just as you clicked on the button, this ph finder will instantly show you accurate results. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. for the concentration of hydronium ions. A pH of less than 7 is considered acidic. What is the pH of this solution? Equation \(\ref{Quad}\) is a quadratic equation with two solutions. Then, we'll find the pH of pure water at 50C from the value of the autoionization constant at 50C. Instead, we often consider two approximations to Equation \(\ref{Exact2}\) that can made under limiting conditions. And to get rid of that log, What are the disadvantages of using a charging station with power banks? Well, look at the reagants in this problem: $\ce{HCl}$, which is essentially just hydronium and chloride, sodium acetate, which as mentioned earlier is essentially just sodium and acetate, and acetic acid. Henderson-Hasselbalch Equation and Example, Acids and Bases - Calculating pH of a Strong Base, Calculating the Concentration of a Chemical Solution, Calculate Concentration of Ions in Solution, Acid Dissociation Constant Definition: Ka, Acids and Bases: Calculating pH of a Strong Acid, Ph.D., Biomedical Sciences, University of Tennessee at Knoxville, B.A., Physics and Mathematics, Hastings College. Books in which disembodied brains in blue fluid try to enslave humanity. So we can plug our pH Use Kb equation \(K_b = \dfrac{[OH^-][B+]}{[B]}\) and ICE table. \end{align}\], \[K_{\large\textrm{a}} = \dfrac{ ({\color{Red} x + y})\, x}{C - x} \label{1}\], \[K_{\large\textrm{w}} = ({\color{Red} x + y})\, y \label{2}\], Although you may use the method of successive approximation, the formula to calculate the pH can be derived directly from Equations \(\ref{1}\) and \(\ref{2}\). This equation is derived from the equilibrium condition for the self-ionization of water, \K_w\). b. The pH value is also equal to the negative logarithm of the hydrogen-ion concentration or hydrogen-ion activity. Calculate the theoretical pH values expected for a 200 m L buffer solution containing a 1:1 ratio of acetic acid and sodium acetate (their concentrations are 0.05 M ), following the addition of; 10 m L of 0.2 M H C l and 10 m L of 0.2 M N a O H. K a of acetic acid is given. It is 0.026M. In most cases, the amount of from the autoionization of water is negligible. \\ Calculate the theoretical pH of each HCl solution, using Equation 5. In other words, does the [H+]=[OH-] concentration equilibrium change depending on the temperature? root of both sides, we find that x is equal to 2.3 times 10 to the negative seventh. In this video, we'll solve for [HO] and pH in two different worked examples. Making statements based on opinion; back them up with references or personal experience. You can select any acid or base from the list of chemicals, or use a known value for the dissociation constant K a or K b. Also, sodium acetate is a soluble salt (see solubility rules), so in the net ionic equation, don't write out the sodium as it is a spectator ion. Use the Henderson-Hasselbach equation to calculate what the pH of the buffer solutions in the remaining beakers should be theoretically: [C,H,O, ) pH calculated = 4.74 + log [HC,H,O, Compare your experimental pHs of . When you add more liquid to a solution, the concentration of the solute is going to decrease. pH? pH measures the concentration of positive hydroge70n ions in a solution. PH is defined as the negative of the base-ten logarithm of the molar concentration of hydrogen ions present in the solution. Accessibility StatementFor more information contact us atinfo@libretexts.orgor check out our status page at https://status.libretexts.org. Choose the option to determine pH with ion concentration in the calculator, and type in any of these four values! When autoionization of water is considered, the method is called the exact pH calculation or the exact treatment. pH of water will not be seven. \begin{array}{cccc} Then, we'll find the pH of pure water at 50C from the value of the autoionization constant at 50C. For each compound enter compound name (optional), concentration and Ka/Kb or pKa/pKb values. A solution is 0.0035 M LiOH. A pH value tells the extent of acidity and basicity of a substance. Everything should be known. since the two are equal. You have the correct number of moles of HCl added (0.002 moles H+) and the correct number of moles of acetate (0.01 moles Ac-). Indefinite article before noun starting with "the". calculate the theoretical Ph of HC2H3O2 using the follwoing equation pH=-log [H3O] and the Ka=1.8x10^-5 for the following Calculate Ka for acetic acid using the meausred ph values for each solution. 10 to the negative 14th. The Wikipedia page on buffer solutions has an example ICE calculation similar to yours towards the bottom of the page. sign over to the left side, which gives us negative 9.25 is equal to the log of the The acid in your car's battery has a pH of about 0.5: don't put your hands in there! This is usually true unless the solutions of strong acids and strong bases are extremely dilute. When given the pH value of a solution, solving for \(K_a\) requires the following steps: Calculate the \(K_a\) value of a 0.2 M aqueous solution of propionic acid (\(\ce{CH3CH2CO2H}\)) with a pH of 4.88. The pH of our stomach varies from 1.5 to 3.5: our stomach is quite acidic! \text{I}& 0.05&x&&0.05\\ To determine pH, you can use this pH to H formula: If you already know pH but want to calculate the concentration of ions, use this transformed pH equation: There also exists a pOH scale - which is less popular than the pH scale. So we would just need to plug The modern apparatus to determine the pH value is a pH meter. What is the pH AND pOH of this solution? You would learn the calculation of pH value in this article.if(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[250,250],'calculatores_com-medrectangle-4','ezslot_9',115,'0','0'])};__ez_fad_position('div-gpt-ad-calculatores_com-medrectangle-4-0'); Different apparatuses are used in the lab to check the pH of a substance. When two or more acids are present in a solution, the concentration of \(\ce{H+}\) (or pH) of the solution depends on the concentrations of the acids and their acidic constants Ka. If you don't know, you can calculate it using our concentration calculator. So we have the pH and our goal is to solve for the concentration of hydronium ions, and pH is equal to the negative log of the concentration of hydronium ions. When solving these problems, being able to identify a reaction will make it 10 times easier. It changes its color according to the pH of the solution in which it was dipped. Use the pH equation which is: \(pH = -\log[H_{3}O^+]\) . Let pH calculator print calculation results and titration curves for further reference. &= 1.8\times 10^{-7} \nonumber First story where the hero/MC trains a defenseless village against raiders, How to pass duration to lilypond function, $\pu{10mL}$ of $\pu{0.2M}$ $\ce{HCl}$ and. \ce{[H+]} &= ({\color{Red} x+y})\\ How dry does a rock/metal vocal have to be during recording? \dfrac{(x )\, x}{0.0010} &= 4.0\times 10^{-11} \label{3'} \\ 10 to the negative 10. Solve for the concentration of H 3 O + using the equation for pH: (5) [ H 3 O +] = 10 p H Use the concentration of H 3 O + to solve for the concentrations of the other products and reactants. Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. step by step solution. For simplicity, we consider two acids in this module, but the strategies used to discuss equilibria of two acids apply equally well to that of two bases. pH of H2SO4 = -log [OH-1] &= 2.2\times 10^{-7}\\ Knowing this, we can say in calculating hydronium concentration in an aqueous solution of a strong acid that the strong acid is the main source of hydronium ions. Acidic solutions have high hydronium concentrations and lower hydroxide concentrations. So that would give us the pH which is 9.25 is equal to the negative log of the concentration of hydronium ions. Created by Jay. What is the pOH of this solution? Solutions with low pH are the most acidic, and solutions with high pH are most basic. Litmus paper gives different colors when dipped in acidic and basic media. ADVERTISEMENTif(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[300,250],'calculatores_com-box-3','ezslot_1',111,'0','0'])};__ez_fad_position('div-gpt-ad-calculatores_com-box-3-0'); All solutions contain a certain pH value that depends on the nature of both solute and solvent. I've always assumed that only PH=7 is neutral. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Calculate the pH when the concentration of the acid is very dilute. OurS272 series of pH sensors deliver reliable online pH monitoring for in-line or submersion installation configuration. \ce{HCc &\rightleftharpoons &H+ &+ &Cc-}\\ You can now recalculate the value for y by substituting values for x and y in Equation \(\ref{Ex1.2}\). Right now, we don't know what But when mixing a chemical solution, you can determine the expected pH using well-studied, well- documented stoichiometric theory. calculate the concentration of hydronium ions in solution, H3O+. \end{align}\], Assume y << x, and x << 0.0010, then you have, \[\begin{align} Use the $K_a$ and its definition to calculate the concentration of $\ce{H+}$, which leads to your pH. calculated it to be 6.64. Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. [H^+] &\approx \dfrac{C}{[H^+]}\: K_{\large\textrm{a}}\\ This question is about the theoretical pH of a buffer solution. In the self-ionization of water, the amphiprotic ability of water to act as a proton donor and acceptor allows the formation of hydronium (\(H_3O^+\)) and hydroxide ions (\(OH^-\)). Calculate the base 10 logarithm of this quantity: log10([H+]). \ce{HA &\rightleftharpoons &H+ &+ &A-};\\ In aqueous solutions of strong acids and strong bases, the self-ionization of water only occurs to a small extent. Why would you only use 10 for the -9.25 part? Combination pH sensors in 12mm glass and plastic bodies are commonly referred to as laboratory style sensors. Solution \ce{HAc &\rightleftharpoons &H+ &+ &Ac-}\\ of hydronium ions, H3O+, is equal to the concentration This online pH calculator is designed to determine the pH of an aqueous solution of a given chemical compound. https://www.thoughtco.com/how-to-calculate-ph-quick-review-606089 (accessed January 18, 2023). Why does secondary surveillance radar use a different antenna design than primary radar? Is the rarity of dental sounds explained by babies not immediately having teeth? Concentration of free H+ ions = 0.1 So even though we used For this problem, using the Henderson-Hasselbalch equation is not really the right way to do it. You'll see why. a neutral substance. It's going to look something like this: $$\ce{HA<->H+ +A-}$$. These colors often inspire colorful pH scales: The ph in our bodies is close to neutral. A solution is 0.00025 M HCl. \text{E}& -&0.04&&0.06\\ The calculator gives the exact pH of the chemical. Acids react with bases, so using that, it isn't too hard to determine what exactly happens in the solution. x &= (0.0010 \times 4.0e^{-11})^{1/2}\\ So we could move the negative However, water is still pKa=. Calculate the theoretical pH values expected for a $\pu{200mL}$ buffer solution containing a 1:1 ratio of acetic acid and sodium acetate (their concentrations are $\pu{0.05M}$), following the addition of; So I just found the $\mathrm{p}K_\mathrm{a}$ for the Henderson equation. Save. 10 to the negative fifth times the concentration of hydronium ions, which we'll just write Anything less than 7 is acidic, and anything greater than 7 is basic. \end{align}\). Solving for x and y from Equations \(\ref{Ex1.1}\) and \(\ref{Ex1.2}\) may seem difficult, but you can often make some assumptions to simplify the solution procedure. Determining and Calculating pH is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts. What happens when 0.02 mole NaOH is added to a buffer solution? \end{align*}\]. One way to start this problem Direct link to siripop's post Why would you only use 10, Answer siripop's post Why would you only use 10, Comment on siripop's post Why would you only use 10, Posted 8 months ago. See this chemical equation below. You usually won't be writing any numbers for your change. General Chemistry:Principles & Modern Applications; Ninth Edition, Pearson/Prentice Hall; Upper Saddle River, New Jersey 07. negative seventh molar. Helvetica. Take the additive inverse of this quantity. (\(\ce{HAc}\) is acetic acid whereas \(\ce{HCc}\) is chloroacetic acid). You will find the description of algorithm used for pH calculations in the pH calculation method section. The procedure to use the pH calculator is as follows: Step 1: Enter the chemical solution name and its concentration value in the respective input field Step 2: Now click the button "Calculate" to get the pH value Step 3: Finally, the pH value will be displayed in the new window What is Meant by pH Measurement? Find [H+] if pH = 8.5, [H+] = 10-pH[H+] = 10-8.5[H+] = 3.2 x 10-9 M. Find the pH if the H+ concentration is 0.0001 moles per liter. Neutralization. Exponentiation involves making everything in the equation the exponent of a certain number we call the base. NOTE: The experimentally determined pH will not always be the same as the calculated pH. Our Rate Constant Calculator will compute the rate constant, the rate of the reaction or the concentration of the substance using the rate laws. When the contribution of pH due to self-ionization of water cannot be neglected, there are two coupled equilibria to consider: \[\begin{align} Here's a derivation of the formula if you're interested that will probably help clear things up a bit. Here's a more in-depth review of how to calculate pH and what pH means with respect to hydrogen ion concentration, acids, and bases. A large \(K_a\) value indicates a stronger acid (more of the acid dissociates) and small \(K_a\) value indicates a weaker acid (less of the acid dissociates). Is it OK to ask the professor I am applying to for a recommendation letter? The pH of an aqueous solution is the measure of how acidic or basic it is. \\ Combination pH sensors are a type of electrochemical pH sensor that feature both a measuring electrode and a reference electrode. 10 to the negative 14th. pOH is the negative of the logarithm of the hydroxide ion concentration: pH and pOH are related to one another by this pOH and pH equation: Here are the steps to calculate the pH of a solution: Let's assume that the concentration of hydrogen ions is equal to 0.0001 mol/L. These sensors work well in light duty applications such as education and research, environmental sampling, and pool monitoring. \text{I}& x& 0.05&0.05\\ Get this widget Build your own widget Browse widget gallery Learn more Report a problem Powered by Wolfram|AlphaTerms of use Share a link to this widget: More Embed this widget It is a strong acid, so it completely dissociates in water. Exact pH Calculations is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts. Apart from the mathematical way of determining pH, you can also use pH indicators. When you're performing pH calculations, always make sure your answers make sense. 10 to the negative 14th at 25 degrees Celsius. and obtained a pH of 6.70, which is greater than 6.65 by less than 1%. A neutralization reaction is when an acid and a base react to form water and a salt and involves the combination of H + ions and OH - ions to generate water. This gives you: Usually, you aren't given the hydrogen ion concentration in a problem but have to find it from a chemical reaction or acid concentration. At 25 oC, the concentrations of both hydronium and hydroxide ions equal \(1.0 \times 10^{-7}\). The pKa to pH converter calculator is an online tool that can find the pH of a liquid solution using the pKa value and concentration. right into this equation. So the concentration of hydronium ions in our solution at 25 degrees Celsius is equal to 5.6 times 10 In this case that is 10 (An unlabeled logarithm is assumed to have a base of 10). Water is a neutral molecule and its pH is 7. not 25 degrees Celsius. that the pH is equal to 9.25. And if we take the square This reaction will result in an increase in the moles of HAc and a concomitant decrease in the moles of Ac- since H+ + Ac- => HAc. Wikipedia addict who wants to know everything. Mendham, J.; Denney, R. C.; Barnes, J. D.; Thomas, M. J. K. (2000). The higher the concentration of hydroxide ions from base molecules, the higher the pH of the solution and, consequently, the higher its basicity. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. \(A^-\) is the conjugate base of the acid. Therefore, the Henderson-Hasselbalch equation can also be written as: An equation that could calculate the pH value of a given buffer solution was first derived by the . The most universally used pH test is the litmus paper. We can also say that in calculating hydroxide concentration in an aqueous solution of a strong base that the strong base is the main source of hydroxide ions. Three different theories define acid and base: The higher the concentration of hydrogen ions from acid molecules, the lower the pH of the solution and, consequently, the higher its acidity. &&y &&y For example, let's say a solution is formed at 25 degrees Celsius and the solution has a pOH of 4.75, and our goal is to Actually, we're going to start with simple stoichiometry as a reaction is occurring. Therefore, \(x + y \approx y\) and 0.100 - y => 0.100. Therefore, after the addition of 10 mL of HCl, the concentration of sodium acetate and acetic acid will no longer be 0.5 M since you diluted the solution a little bit. Petrucci, Ralph H., Herring, Goeffrey F., Madura, Jeffrey D., and Bissonnette, Carey. Use pH calculator to calculate the shape of virtually any acid/base titration curve. of hydronium ions times the concentration of \[\dfrac{K_w}{[H^+]} < 1 \times 10^{-8}.\]. The concentration of a substance can be specified either in moles or in units of mass per unit volume. The ion product of water, \(K_w\), is the equilibrium condition for the self-ionization of water and is express as follows: \(K_w = [H_{3}O^+][OH^-] = 1.0 \times 10^{-14}\) . To simplify the process, we're going to assume the reaction reacts to completion, and then reverses until it reaches equilibrium. Here's How to Calculate pH Values. Let's assume that it's equal to. Jay is exponentiating the equation to solve it. pH, commonly used for water measurements, is a measure of acidity and alkalinity, or the caustic and base present in a given solution. Tech geek and a content writer. You may have attempted to use the approximation method: \[\begin{align*} These online calculators calculate the pH of a solution. Enter the concentration of hydrogen or hydroxyl ions released in the solution or the simple molarity of the solution and press the "calculate" button. pH = - log10([H+]). However, the amount of \(\ce{H+}\) ions from water may be very small compared to the amount from an acid if the concentration of the acid is high. \ce{[H+]} &= x + y\\ of free H+ ionsif(typeof ez_ad_units != 'undefined'){ez_ad_units.push([[250,250],'calculatores_com-banner-1','ezslot_5',127,'0','0'])};__ez_fad_position('div-gpt-ad-calculatores_com-banner-1-0'); Let us calculate the pH value of 0.05M H2SO4 solution, H2SO4 2H+ + SO4- \text{C}& -0.01&x-0.01&&+0.01\\ An acid is a species that donates a proton in a solution while a base is a specie that dissociates OH ions in the solution. This is small indeed compared to \([H^+]\) and \(C\) in Equation \(\ref{Exact}\). Since Kw is temperature dependent, if the temperature is something other than 25 degrees Celsius, the If you're seeing this message, it means we're having trouble loading external resources on our website. Basic solutions have high hydroxide concentrations and lower hydronium concentrations. That only applie, Comment on Richard's post Correct. { Acid_and_Base_Strength : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.
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theoretical ph calculator