Prepartion of Primary Standard

Experiment 2 Preparation of Primary Standard solutions and Standardizing Acid and Base solutions Objectives The objective of this sample is 1- To prepare two primary normal solutions, KHP and Na2CO3 2- To standardize a sodium hydroxide solution using the prepared primary standard KHP. 3- To standardize a hydrochloric acid solution using the prepared primary standard Na2CO3. 4- To calculate the concentration of an unknow acid or base. Introduction A primary standard is a standard that is accurate enough that it is not calibrated.For a compound to be considered as a primary standard it should have several grave characteristics, the most important of which are high purity, stability, low hygroscopicity, high solubility, and high molar view. A primary standard solution is a solution of cognize concentration made from a primary standard. Primary standard solutions are used in determining the concentrations of other solutions to an extremely high accuracy. They are typically used in titrations and other analysis techniques as standardization solutions.A secondary standard solution, such as HCl solution, is a solution which must be convertible first against a primary standard, but afterwards, it ordain be stable enough for titrimetric work (Titration). Titration involves the gradual addition of a solution of accurately known concentration (standard solution) to another solution of unknown concentration (or vice versa), until the chemical response is complete. Titrations are based on reactions which go to completion rapidly. A reaction is complete when stoichiometric amounts of the reacting substances are combined.This is the stoichiometric point (equivalence point) in the titration. The equivalence point is detected visually using an indicator. An indicator is a substance (added at the beginning of the titration to the flaskful) that changes color at (or very near) the equivalence point. The point where the indicator actually changes color is called the end p oint of the titration. In this experiment, two primary standards will be used. The first is potassium hydrogen phthalate (KHC8H4O4, abbreviated as KHP, molar mass = 204. 23 g/mol), an acid primary standard which will be used to standardize a sodium hydroxide solution.The structure of KHP is shown below O COH CO K O The chemical equation of the reaction eject be written as KHP(aq) + NaOH(aq) ? Or, expressed as a net ionic equation, HP-(aq) + OH-(aq) ? P2-(aq) + H2O(l) The second primary standard to be used is sodium carbonate, Na2CO3 (molar mass = 105. 99), a base, by which a hydrochloric acid solution will be standardized. The chemical equation of the reaction is 2HCl(aq) + Na2CO3(aq) CO2 (g) + 2NaCl(aq) + H2O(aq) KNaP(aq) + H2O(l) The reaction above yields CO2, which dissolves into the solution to generate an acid.The presence of dissolved CO2 thus interferes with the pH and the detection of the end point of the titration. However, the CO2 can be driven off by change state the solution, enabling an accurate titration. Procedure I. Standardization of NaOH a. Preparation of the acid primary standard 1. Obtain a bottle containing 2g of KHP and measure it with the cap on the uninflected balance. Record the mass in hedge 2. I. 2. slay the unanimous KHP to a 100. 0 mL volumetric flask using a funnel, re-stopper the bottle and weigh it. Record the mass in Table 2. I. 3.Rinse the funnel to wash any sticking solid using a washing bottle and add to a greater extent dis processed urine into the volumetric flask to dissolve the KHP (1/2 its capacity). Swirl the flask make sure to dissolve the solid completely. Add more(prenominal) water (2/3) and spin again. Dilute to the mark carefully, stopper or cover with a parafilm paper and invert several times with swirling to equalise the KHP solution. b. Preparation of an approximately 0. 1 M NaOH solution 1. Obtain about 6 mL of a 50 % (w/v) NaOH solution in a clean and modify graduated cylinder from the stockroom . Transfer the NaOH to a clean 1L polyethylene bottle.Fill the rest of the polyethylene bottle with double distilled water to the mark. Shake thoroughly to homogenize. 2. Rinse your buret, after washing it with distilled water, with few mL of the NaOH solution allow some solution to flow out through the lower end. Fill the rinsed buret with NaOH, make sure that the tip is filled with no air bubbles. c. Standardization of NaOH 1. Pipet a 10. 00 mL aliquot of the primary standard KHP solution into a one hundred twenty-five mL Erlenmeyer flask. Add 25 mL of distilled water and two drops of phenolphthalein indicator. Record the buret course session (use a white card as background to make haste reading the buret).Put a white cover or paper below the Erlenmeyer flask and start titrating by adding NaOH continuously and with constant swirling of the flask. A pink color appears locally and disappears on swirling continue titration till a faint pink color persists. Take the lower reading of the buret. The first titration is usually a rapid one. 2. Repeat the titration slowly three more times. Record data in Table 2. II. 3. Calculate the average molarity. II. Standardization of HCl a. Preparation of the base primary standard 1. Obtain a bottle containing 1g of dry Na2CO3 and weigh it with the cap on the analytical balance.Record the mass in Table 2. III. 2. Transfer the solid Na2CO3 to a 100 mL volumetric flask using a funnel, re-stopper the bottle and weigh it. Record the mass in Table 2. III. 3. Rinse the funnel to wash any sticking solid using a washing bottle and add more distilled water into the volumetric flask to dissolve the Na2CO3 (1/2 its capacity). Swirl the flask make sure to dissolve the solid completely. Add more water (2/3) and swirl again. Dilute to the mark carefully, stopper or cover with a parafilm paper and invert several times with swirling to homogenize the solution. b.Standardization of HCl 1. Get around 200 mL of HCl solution using a beaker a nd cover with a watch glass. 2. Rinse your buret, after washing it with distilled water, with few mL of the HCl solution allow some solution to flow out through the lower end. Fill the rinsed buret with HCl, make sure that the tip is filled with no air bubbles. 3. Pipet a 10. 00 mL aliquot of the primary standard Na2CO3 solution into a cxxv mL Erlenmeyer flask. Add 25 mL of distilled water and two drops of bromocresol green indicator. Record the buret reading (use a white card as background to facilitate reading the buret).Put a white cover below the Erlenmeyer flask and start titrating by adding HCl continuously and with constant swirling of the flask until a change of color from blue to faint green. Boil the solution to free CO2. The color should return to blue. Carefully add HCl from the buret until the solution turns green again and report the volume of acid at this point. Keep the solution as reference for color for the other titrations. 4. Repeat the titration slowly three m ore times. Record data in Table 2. IV. c. Titration of blank 1. Add to a 125 mL Erlenmeyer flask 50 mL of distilled water and two drops of bromocresol green ndicator. Titrate with your HCl solution to faint green. Subtract the volume of HCl needed for the blank from that postulate to titrate Na2CO3. 2. Calculate the mean HCl molarity. III. Determining the concentration of an unknown a. Qualitative identification of the unknown 1. Obtain an unknown from the stockroom and record its number in the report. Add two drops of the phenolphthalein indicator. 2. Identify if it is an acidic or a basic unknown. Record your observation. b. Titration of the acidity in an unknown acid solution 1. Fill your burette with either HCl or NaOH according to your observation in the previous part. . Pipet a 25 mL aliquot of the unknown solution into a 125 mL Erlenmeyer flask. Add two drops of the needed indicator (either phenolphthalein or bromocresol green). Record the buret reading (use a white card as background to facilitate reading the buret). Put a white tile or paper below the Erlenmeyer flask and start titrating by adding HCl or NaOH continuously and with constant swirling of the flask until a change of color according to the indicator being used. Record the lower reading of the buret. (Note if your unknown is a base, remember to boil the solution as in part II. before proceeding with the titration to the end) 3. Repeat the titration slowly three more times. Record data in Table 2. V. Reference Harris, Quantitative chemical Analysis, 7th Ed. Student Name______________ Student ID _______________ Experiment 2 Date_____________ Section___________ Preparation of Primary Standard solutions and Standardizing Acid and Base solutions Purpose Data and calculation I. Standardization of NaOH Table 2. I Preparation of the acid primary standard Mass of vial + cap + KHP Mass of vial (empty)+ cap Mass of KHP hatful of solution M KHP = ___________________ Table 2.II Standardization of the NaOH Solution Trial 1 2 3 Upper buret reading (mL) Lower buret reading (mL) Volume of NaOH (mL) Volume of KHP aliquot =________________________ V NaOH = ____________________________________ ______________________________ M NaOH (average) = II. Standardization of HCl Table 2. III Preparation of the base primary standard Mass of vial + cap + Na2CO3 Mass of vial (empty)+ cap Mass of Na2CO3 Volume of solution M Na2CO3 = ___________________ Table 2. IV Standardization of the HCl Solution Trial 1 2 3 Upper buret reading (mL) Lower buret reading (mL) Volume of HCl (mL) Volume of HCl for blank (mL)Volume of Na2CO3 aliquot =_________________ V HCl = ___________________________________ M HCl (average)= ____________________________ III. Determining the concentration of an unknown unfathomable = Unknown identity = Volume of unknown (aliquot) = Table 2. V Determination of the Concentration of an Unknown Trial 1 2 3 Upper buret reading (mL) Lower buret reading (mL) Volume of HCl or NaOH (mL) Volume for blank (mL) V standard (average) = _______________________ M unknown (average) = _____________________________