5 g of NaF was added to displace Mg2+ from its EDTA complex. pH control provides some selectivity for EDTA titrations. Select which component of the buffer will have given concentration. Add 2-3 cm 3 of the buffer (pH 10) solution (measured out using the graduated. (a)Describe how pH can be measured with a glass electrode?. 5 highlights. For the titration of Mg2+, one must buffer the solution to a pH of 10 so that complex formation will be quantitative. But since these topics are intimately dependant on the properties of. We will also need indicator - either in the form of. 5 mM MgCl 2, 10 mM KCl, and 0. Explanation. Use lots of agitation and a relatively slow addition of the titrant. NOTE: For best results, all solutions should be at the same temperature. Complexometric Titration with EDTA In this experiment you will use ethylenediaminetetraaectic acid (EDTA) to determine metals in aqueous solution by complexation titration. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Calculate or sketch titration curves for 25. This buffer could be further optimized in later stages of development. titration of the metal ions in the lake water. At what pH the hardness of water is estimated by EDTA method? How this pH is maintained? A. EDTA forms complexes with metal ions in basic solutions. Why? Endpoint is not the same as equivalence point. Because all reactions between metal ions and EDTA are pH dependent. solution is kept nearly constant by adding a basic buffer NH. Add 5ml of buffer solution and 3 drops of eriochrome black T indictor. IntroductionVolumetric analysis Simple and easy Fast and can be done on site Less expensive Estimation of content or Assay Precise and accurate Depends on method and specificity. It shows a color change from red to blue in the pH range 7-11. Buffer, pH 10. I am a teacher and can't seem to figure out this problem, although I know I did it once before. An "indicator" is a chemical that changes color as conditions in the solution change. For Co2+, this corresponds to a pH greater than 4. Li/EDTA titrations /P 8 Effective EDTA titration See Fig 13-9: Minimum pH for effective EDTA titration of various metal ions at 0. If the titration is to be used to demonstrate the relative values of formation equi-librium constants, add the first 20 mL of the EDTA solu-. Koehler K90500 / K90590 TAN-TBN Titrator. Add about 2 cm 3 of pH 10 buffer, 10 cm 3 of Mg-EDTA Indicator solution and 3 drops of Eriochrome Black T indicator. The method you will use to determine the Ca2+ concentration in the two saturated CaSO 4. Full text of "Calculations Of Analytical Chemistry" See other formats. Why is the Ammonia/Ammonium buffer (pH≈9. Take out the glass electrode from this buffer solution and wash it with distilled water, dry it gently with tissue paper and again use another buffer solution of known pH (say 9. This may not sound simple at all. A) If Pb2+ is the only metal contaminant, is this pH appropriate for this titration? Why or why not? 3 pts. Dip the electrode in buffer solution of pH 4. 25 g/mol, is the most used polyaminocarboxylic acid in metal chelation. titration curve is a graph of pM (= -log[Mn+]) versus the volume of added EDTA. The question im stuck on follows: 5. Indicator - either in the form of solution, or ground with NaCl -100 mg of indicator plus 20 g of analytical grade NaCl. pdf), Text File (. ) is commonly determined by the titration of a water sample with a standardized solution of the disodium salt of ethylenediaminetetraacetic acid (EDTA) using eriochrome black T or calmagite as an indicator. Calculate the weight of Na2H2EDTA-2H2O needed to make up 250 mL of a 0. Buffer for Determination of iron: Buffer pH 5. If a buffer has more base than acid, more OH-ions are likely to be present and the pH will rise. The equivalence point occurs between pH 8-10, indicating the solution is basic at the equivalence point and an indicator such as phenolphthalein would be appropriate. 5 mM MgCl 2, 0. It has four carboxyl groups and two amine groups that can act as electron pair donors (Lewis. Add 10 mL of ammonia buffer, 50 mL of distilled 4. 0´ 10-6) plus 0. EDTA Titrations: An Introduction to Theory and Practice, Second Edition considers the theoretical background, full procedural details, and some practical applications of EDTA titrations. determination of calcium by titration with EDA. 00 x 10-4 M EDTA solution. The directions contained here will make a 0. To solve for the pH we need to use the K b of CH 3 COO-and its concentration. The first choice we have to make is that of the nature and the pH of the buffer system we want to use. txt) or read online for free. It derives its stability in part to calcium being connected to the EDTA by six bonds. As before, add some indicator, 5 mL of pH 10 buffer, and 15 drops of 0. 5 with acetate buffer. EDTA is ethylene diamine tetraacetic acid or H 4C 10H 12N 2O 4. In that titration, pH of a test sample solution containing $\ce{Pb^2+}$ and $\ce Remember, during the titration, with out "real" buffer, pH of the solution changed due to release of $\ce{H+}$ ions by complexation. 6H20 be added to the EDTA solution? 2. 4, most EDTA exist non Y4- pH is adjusted to 5. Add 4-5 drops of the calmagite indicator solution and titrate with EDTA to the blue end point. The online questions are identical to the textbook questions except for minor wording changes necessary for Web use. Below are the reactions that occur during the titration where H. 25 g/mol, is the most used polyaminocarboxylic acid in metal chelation. 1 M sodium phosphate buffer (from 1 M stocks) at 25°C. I have used a virtual lab and know that you need 71 ml of acetic acid and 29 ml of NaOH, but dont know how to calculate it. Slides 2-6. The mean corrected titration volume was 15. Recipe can be automatically scaled by entering desired final volume. To perform titration we will need titrant - 0. EDTA - ethylenediaminetetraacetic acid (1:1 mol ratio between divalent metal (Ca 2+, Mg ) and EDTA). 7 mL to reach said point. Why is all glassware acid washed? Because metal ions can adsorb to glassware, react with EDTA and mess up the experiment. Each flask was then titrated with EDTA from a wine-red color to a blue color endpoint. Correlate the stability of the Mg-EDTA, Ca-EDTA, Mg-EBT, and Ca-EBT complexes with the values of the formation constants. There are a few ways of measuring water hardness. The solution turns yellow when a few drops of indicator are added. The pH of an acid base titration is measured at a set volume interval of titrant added, the curve of the graph varies depending on the conditions of the titration, say weak acid strong base, or strong acid weak base and so on. To maintain the pH at around 10, a buffer soluton is required for the titration. Why is the Ammonia/Ammonium buffer (pH≈9. 5 mM MgCl 2, 0. 1 μM GST-TcPINK1 where indicated. 01 M EDTA solution and ammonia pH 10. 0 1M 1,25 ml MPS2 for 10 ml 0,2 N NaOH 10N 200 ml 1% SDS 10% 1 ml H2O 8,8 ml MPS3 for 100 ml. FR7 | Ethylenediaminetetraacetic Acid | Titration idk. Erichrome Balck T indicator added and solutino titrated with EDTA Why do both these methods need sodium hydroxide/pH10 buffer? I. What is the purpose of auxiliary complexing agents? What reagent, if any, served as auxiliary complexing agent in this titration? Discuss. Europe PMC is an archive of life sciences journal literature. It is made by mixing a large volume of a weak acid or weak base with its conjugate base or acid. For example, in cation exchange chromatography, using a functional group on the solid support with a pKa of 1. Answer to: Why is a buffer solution added in EDTA titration? By signing up, you'll get thousands of step-by-step solutions to your homework. Wear your goggles! Stock Chemicals Used Chemical Maximum Amount Used 6 M Hydrochloric Acid <6 mL EDTA Disodium Salt (dihydrate), (Solid) <10 grams Calcium Carbonate, (Solid) 0. The total water hardness determination is done at pH of around 10, using an ammonia-ammonium chloride buffer. Principles of Titration and errors By Dr. Buffer for Determination of iron: Buffer pH 5. The equivalence point occurs between pH 8-10, indicating the solution is basic at the equivalence point and an indicator such as phenolphthalein would be appropriate. I have been preparing 0. Mix thoroughly. 7) necessary when carrying out the Mn2+ EDTA titration? Hint: Look up a fractional composition. Would this titration work if the sample pH was 4? Explain why/why not. Complexometric titration: the titration which involves the formation of complexes is known as Complexometric titration. Statistical analysis of EDTA titration vs. Take out the glass electrode from this buffer solution and wash it with distilled water, dry it gently with tissue paper and again use another buffer solution of known pH (say 9. 5 Molar means that there is a half a mole of EDTA molecules in the 1 liter solution. Click here 👆 to get an answer to your question ️ Why we use buffer solution in complexometric titration? 1. 0500 M Mn+ with 0. Most automatic titration automation solutions cover only some of these steps, such as the titration itself and the changing of samples. In the simplest terms, a titration curve is basically a plot of the volume of titrant that you're adding to the analyte versus pH. Replace and tighten the cap on the buffer solution bottle. 7 mL to reach said point. Where such a series of measurements is plotted correctly (i. Below are the reactions that occur during the titration where H. 0000000000000002e-5 0 0 0 0. EDTA titration w/ CoCl2 6H2O: Why did I need sodium acetate and HCl? Hi, /chemhelp! Why do you think a buffer is necessary in this case? level 2. 00 and pH 10. 01 M EDTA until the color change from wine-red to blue. 025 molL-1 magnesium chloride solution until a. 0 (use of a pH meter is recommended) and dilute to 1 liter. If the titration is to be used to demonstrate the relative values of formation equi-librium constants, add the first 20 mL of the EDTA solu-. An example is the titration of Ca2+ which takes place at pH 9 in a buffer medium whose composition takes into account the behavior of the indicator electrode used. After centrifugation, cells were resuspended in 2 cell pellet volumes of buffer A and lysed by Dounce homogenizer (B type pestle) with homogenate checked by microscopy. The most effective pH range for a buffer is generally one pH unit and is centered around the pKa for the system. Describe the displacement method in EDTA titration for the Ca2+ determination with EBT as indicator, and give the reason to state why a direct titration method is not used. 01M EDTA solution until a pure blue color is obtained with no tinge of purple. Calculate the weight of Na2H2EDTA-2H2O needed to make up 250 mL of a 0. distilled water, followed by 15ml of pH 10 buffer. can function properly. This may not sound simple at all. 00, if C Fe3+ = 1. desiccator when you are through with it. 0500 M Mn+ with 0. References: L. 0 (use of a pH meter is recommended) and dilute to 1 liter. The procedures I can find online all use ammonia-ammonium chloride buffer. To adjust the pH of the enzyme reaction buffer. So we need a basic solution to facilitate the loss of H+ from the EDTAH4 to give [EDTAH2]2-. You need 1 ml of every dilution and stock solution (0. 01 M EDTA solution and ammonia pH 10. why must MgCl2. Find the pH of the resulting buffer. Europe PMC is an archive of life sciences journal literature. Search worldwide, life-sciences literature Search. You should then titrate this with the EDTA solution until a definite colour change occurs. 7 mL to reach said point. In addition dissolved impurities such as Cu(II) or Fe(III) will interfere. An example is the titration of Ca2+ which takes place at pH 9 in a buffer medium whose composition takes into account the behavior of the indicator electrode used. In the EDTA titration of Ca2+ and Mg2+ in natural waters (Lab). ICP-AES in the pH 10 Buffer: To create a pH 10 buffer solution 142 mL of 28 wt% aqueous NH 3 and 17. pdf Put your unknown in the oven at 150 °C for at least 30 minutes, while you prepare your EDTA solution and do your standardization titrations. 00 mL of the Ca 2+ standard solution into an Erlenmeyer flask 2. We'll take ethanoic acid and sodium hydroxide as typical of a weak acid and a strong base. Below are the reactions that occur during the titration where H. In detergents and soaps, complexing agents such as EDTA are used for reducing the hardness of water by removal of undesired metal ions. 0100 M NaOOCH 3 at pH 7. Finally, titrate an aliquot that has been brought to a pH of about 1. 0100 M Mg2+. 50ml of water with 4ml of 1. 01005 Molar, Aqueous 2 Product Choices. 140 ×10-3 M EDTA for titration. Buffer solutions are used to calibrate pH meters because they resist changes in pH. EDTA, or Ethylenediaminetetraacetic acid, is widely used in textile, pulp/paper, food and pharmaceutical industries. 0400 M EDTA solution are added to the titration mixture. 0500 M EDTA, assuming K. 00 and pH 10. Note: For any weak acid-strong base titration, the pH at the equivalence point will be greater than 7 because the conjugate of the weak acid is a base. EDTA, the titrant, complexes with Mg and Ca cations, removing them from association with the indicator. In most water samples, calcium and magnesium are the chief contributors to water hardness. A preview of an experiment exploring the capabilities of buffer solutions, and the method of pH titration. 17, along with the details of glass and calomel electrodes. Keep it under the fume hood as much as possible and avoid breathing its vapors. Therefore, at neutral pH all four of the carboxyl groups are deprotonated, and one of the amine groups is partially deprotonated (HY-3 form). Thus, if the solution is buffered to about pH 10. To each sample, add 3 mL of pH 10 buffer and 6 drops of Eriochrome black T indicator. What is the purpose of auxiliary complexing agents? What reagent, if any, served as auxiliary complexing agent in this titration? Discuss. 050 mole of its conjugate base in 1 liter of solution. Titration & Karl Fischer; added to the phenol. There are three natural regions of the titration curve. Only the indium is complexed under these conditions. At pH=10 one proton is present and the color of the indicator is blue. Where such a series of measurements is plotted correctly (i. 28 and comment on the effect of pH and of NH 3 on the titration of Cd 2 + with EDTA. Below are the reactions that occur during the titration where H. If needed, a few drops of 1-M NaOH can be added to bring the pH to 10. The pH of 10 is achieved by the use of an aqueous ammonia-ammonium buffer mixture. Mix thoroughly. Recommendations for the setting of the pH value of a buffer 5 • Temperature • Titration • Ionic strength • Buffer additives • pH meter control Criteria for the selection of a buffer 6 • Selection of a buffer for the correct pH range • Determination of the pH optimum of an enzyme. Add 6 drops of EBT indicator. Slides 2-6. There should not be any leakage from burette 4. This means neither the base nor acid concentration will be more than 10 times greater than the other. Mix thoroughly. Try to use an imidazole step gradient. Add 20 mL of 0. 04398 L of NaOH. The acetate buffer would be effective of the pH range from about 3. In detergents and soaps, complexing agents such as EDTA are used for reducing the hardness of water by removal of undesired metal ions. If preparation of such sample is difficult, we can use different EDTA concentration. Im completely lost and just about guaranteed to fail if i dont get this. Procedure to follow: Weight exactly about 0. 0200 F Cu2+ at pH 5. Take out the glass electrode from this buffer solution and wash it with distilled water, dry it gently with tissue paper and again use another buffer solution of known pH (say 9. The conjugate acid of Tris has a pK a of 8. If a buffer has more base than acid, more OH-ions are likely to be present and the pH will rise. You need 1 ml of every dilution and stock solution (0. In this experiment, pH 10 buffer is used to keep the pH around 10 so EDTA and Eriochrome Black T. Carbonic acid, H2C03 has two pKa values, 6. 00 and pH 10. Determine the total hardness (Ca2+ and Mg2+) by using a volumetric pipet to pipet 25 mL of the unknown solution into a 250 mL Erlenmeyer flask. Weak Acid Strong Base Titration Curve - pH is greater than 7 at the equivalence point 10. Color change at the end point : red to blue b)Determination of the Calcium Procedure. 0-01M Magnesium Chloride. Recipe can be automatically scaled by entering desired final volume. Can someone explain why EDTA needs basic condition for dissolving? high once you put it in water, unless you do use a buffer, you're likely to be in this stage : the minimum pH for an. Determination of Hardness of Water by EDTA Titration/Complexometric Titration. By: Andie Aquilato. ) is commonly determined by the titration of a water sample with a standardized solution of the disodium salt of ethylenediaminetetraacetic acid (EDTA) using eriochrome black T or calmagite as an indicator. 00 mL of the Ca 2+ standard solution into an Erlenmeyer flask 2. Full text of "Calculations Of Analytical Chemistry" See other formats. Neither titration includes an auxiliary complexing agent. This buffer could be further optimized in later stages of development. Repeat 2 more times, or until pH does not changes after heating. The buffer adjusts the pH to ensure that the reaction goes to completion. Minimum pH required for quantification i. During a buffer, why will the pH remain constant? because there exists an equilibrium between the weak acid and its conjugate base. Initially, the pH of the sample is adjusted to >10 using an ammonium hydroxide-ammonium chloride buffer. EDTA, the titrant, complexes with Mg and Ca cations, removing them from association with the indicator. Indicator - either in the form of solution, or ground with NaCl -100 mg of indicator plus 20 g of analytical grade NaCl. Then add 4 drops of EBT (Eriochrome Black T) indicator and titrate with standard 0. The temporary hardness can then be found by subtracting the permanent hardness from the total hardness value. Examine the different forms of phosphate salts and some buffering system pH ranges. Then add 10 drops of the Na 2MgY reagent and 12 drops of the freshly made Calmagite indicator solution, and stir. Locate the equivalence. 5 with acetate buffer. The total water hardness determination is done at pH of around 10, using an ammonia-ammonium chloride buffer. A mole is equal to 6. Complexometric titration: the titration which involves the formation of complexes is known as Complexometric titration. 2 g/mole). 5, the average pH of saliva; the formation constant of the Zn-EDTA complex is 10° at this pH. during the complexometric titration using edta it is very necessary to maintain the ph of the solution near about 10 so we use ammonium chloride buffer if we will not use this buffer dring the. To each 50mL aliquot, add about 2mL of pH 10 buffer and 4 to 5 drops of Eriochrome Black T or Calmagite indicator. What is the name of the buffer used in EDTA titration? Ammonium chloride - Ammonium hydroxide. Europe PMC is an archive of life sciences journal literature. The titration curve shown in the figure below illustrates the titration of the weak acid buffer solution we just stepped through. As we need Y4- to react w. But since these topics are intimately dependant on the properties of. In acid-base titrations the end point is detected by a pH sensitive indicator. Because EDTA has four acidic protons, the formation of metal-ion/EDTA complexes is dependent upon the pH. Rinse the body of the electrode so that any sample remaining on the electrode is returned back into the flask. A buffer solution is formed containing excess ammonia and ammonium chloride. Sodium Borate Buffer is a buffer that is used to maintain the pH within a relatively narrow range. What is the pH after 10. Pipet (using glass transfer pipet) 10. Why is hardness important? Measure of quality of water for household and industrial use (hard waters can precipitate calcium carbonate which can clog filters, pipes, etc. This video demonstrates the titration of calcium with an EDTA titrant. The color change or other effect should occur close to the equivalence point of the reaction so that the experimenter can accurately determine when that point is reached. pH~10 is blue, when it forms a complex with a metal ion it turns red. With this it can be said that cations with charge 2-3+ are titrated better at pH 3-10. Let the titre value be V1ml. 8 mL of the 1. 3 mL of ammonia/ammonium chloride buffer (pH 10) is added to the mixture prior to the titration to capture the calcium metal ions so the indicator can work properly. This is important in basically two scenarios: There is no magnesium in your sample. What is the concentration of the #NaOH#?. ) is commonly determined by the titration of a water sample with a standardized solution of the disodium salt of ethylenediaminetetraacetic acid (EDTA) using eriochrome black T or calmagite as an indicator. Add the same amount of indicator to all samples. In that titration, pH of a test sample solution containing $\ce{Pb^2+}$ and $\ce Remember, during the titration, with out "real" buffer, pH of the solution changed due to release of $\ce{H+}$ ions by complexation. Determining the total hardness in water using complexometric titration with EDTA tutorial suitable for chemistry students. The completely deprotonated form of EDTA, Y 4-, can form bonds through the lone pairs of electrons on the 4 oxygen atom and 2 nitrogen atoms for a total of 6 binding sites. You will be using a pH electrode attached to the LabQuest2 interface and computer as a pH meter in this experiment. The calcium in the water will be measured by performing a titration with EDTA. Click here 👆 to get an answer to your question ️ Why we use buffer solution in complexometric titration? 1. The titration curve, expressed as pH or E vs volume of titrant, yields an S-shape plot. 45 and pKb2 = 8. A simple phosphate buffer is used ubiquitously in biological experiments, as it can be adapted to a variety of pH levels, including isotonic. If the concentration of the titrant is known, then the. The end point is observed by a loss of the bluish violet color as the last of the lead-Erio-T complex is consumed. I naf s th a Chitiiii a At t, 460 Llrcvicr Publishing Coinpeny Amsterdan l'rintLd in I-lie NulicrIand Compleximetric determination of nickel with copper (I I)-EDTA-TAR as indicator For the titration of nickel with EDTA, murexidel, pyrocatechol violet`, pyr rogallol red', bromopyrrogallol red', eriochrome red BS and the copper(II)-EDTAPAN system' have been recommended as indicator. The lead is titrated with standard EDTA. Complexometric titrations with EDTA have been reported for the analysis of nearly all metal ions. 30 M pH = 5 6. Using ITC Technique for Characterization of Protein-Protein. The ammoniacal buffer, pH 10, was prepared with 54 g of NH4C1, plus 350 ml of concentrated ammonia, and water to 1 liter. 02M EDTA solution at pH 10, primary standard, NH 3-NH 4 Cl buffer solution. (b) A buffer was prepared by 0. Full text of "Calculations Of Analytical Chemistry" See other formats. And so make the reaction go forward “towards the formation of complex”. The titration is conducted by measuring the pH with a glass electrode. Please consult. 00, the pH really is 7. solution is kept nearly constant by adding a basic buffer NH. Complexometric titration (sometimes chelatometry) is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Eriochrome Black T has also been used to detect the presence of rare earth metals. The temporary hardness can then be found by subtracting the permanent hardness from the total hardness value. 05 M of Na2C03 is titrated with a 0. distilled water, followed by 15ml of pH 10 buffer. In this case, the magnesium concentration in the reaction should be increased to compensate for this eff-. To avoid change of the color of the indicator with the change of PH. 13 Answers ;. txt) or read online for free. If preparation of such sample is difficult, we can use different EDTA concentration. Next, an indicator solution (Eriochrome Black T or calmagite) is added. Quantitatively transfer this into a 250 mL volumetric flask then add 2-3 mL of pH 10 ammonia buffer. Hence, a buffer solution of pH 10 is necessary during titration for Ca++ & Mg++ so that it will not allow the decrease of pH. 1 mM mM phosphate ions, while regular PBS is 10 mM phosphate. Total hardness determination. With this it can be said that cations with charge 2-3+ are titrated better at pH 3-10. When hard water passes through a column filled with small granules of resin, the Ca and Mg ions are exchanged for sodium ions RNa2 + Ca2+ RCa + 2 Na+ Reaction before the titration Ca+2 + EDTA-4 -----> CaEDTA-2 end point of the titration Mg In + EDTA-4 -----> MgEDTA-2 + In-2 from the top of the tank water flows through a sand filter where also. Calculate the weight of Na2H2EDTA-2H2O needed to make up 250 mL of a 0. Explanation: A complexometric titration uses the formation of a coloured complex to indicate the endpoint. 3, most of the EDTA will exist as Y4- ions. Place the beaker on a magnetic stirrer and add 0. • Temperature • Titration • Ionic strength • Buffer additives • pH meter control affecting the functioning of the system under investigation. Neither titration includes an auxiliary complexing agent. In the EDTA titration, it is assumed that the total hardness is due to the presence mainly of calcium and magnesium ions. A buffer solution is formed containing excess ammonia and ammonium chloride. Would this titration work if the sample pH was 4? Explain why/why not. an ammonia – ammonium chloride buffer to bring the pH to 10. The preparation of meter calibration standards pH 4, pH 7, and pH buffer solutions 1 - 13. To one sample add 1 mL EDTA to complex any aluminium present. What is the Total Water Hardness of the water sample (in units of M)?. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Mg 2+ + EDTA 4-→ MgEDTA 2-Titration is done in pH 10 solution. 0 mL of pH 10 buffer. 3 because its pK a shifts to 8. 1 M sodium phosphate buffer (from 1 M stocks) at 25°C. The total hardness of water (i. Be-cause pH = pKa at 50% dissociation, a. Not much of information lol. Standardization of EDTA will be performed first and then the determination of calcium concentration. Taking H4Y and H3In as the formulas for EDTA and. The volume of. The Buffer solution is used to resist the change in pH. How to calculate the unknown concentration when you don't have a 1:1 molar ratio of H+ to OH-. why and how will the % purity be in error? 9(c) Pure calcium carbonate can be used to make a standard calcium ion solution to practice a complexometric titration of calcium ions with EDTA or determine the molarity of the EDTA reagent. 1 AWWA EDTA Titrimetric Method a. Determination of Total Hardness by Titration with Standardized EDTA. After the addition of Calmagite indicator the solution required 21. To avoid change of the color of the indicator with the change of PH. 1 M NaOH (5), and the volume of NaOH which must be added to reach a pH of 5. Questions left blank are not counted against you.