Unsure how to calculate the pKa from pH please explain Pre-Laboratory AssignmentPhosphoric acid is a triprotic acid (three ionizable hydrogens). The values of its stepwise ionization constants areK₁₁ = 7.5 × 10-¹³, K₂ = 6.2 x 10-8, and K, = 4.2 × 10-1³,1. Write the chemical equation for the first ionization reaction of phosphoric acid with water.H₂PO4+H₂O H₂0++H₂O ++ H₂PO₂2. Write the equilibrium constant expression (K,,) for this reaction.hai= [H₂O+][H₂ POITECH3PO4J3. What would be the pH of a solution when [H,PO,] = [H₂PO4]? Note: pH = -log[H₂O*].pH = -log(7.5x10³) = 2.134. Phenolphthalein would not be an appropriate indicator to use to determine K, for phosphoric acid. Why not? Choose asuitable indicator from the following color chart.IndicatorPhenolphthaleinMethyl RedOrange IV12Red34ColorlessPeach5pH6Orange78PinkYellow9Yellow10Red11OrangePhenolphtalein is colorless until the pH is about 8, the prtCf phosphovic acid is 2.13, so a suitable indicator wouldOrange IV©2015 Flinn Scientific, Inc. All Rights Reserved. No part of this material may be reproduced or transmitted in any form or by any means, electronic or mechani-cal, without permission in writing from Flinn Scientific, Inc. Student pages may be shared only by the instructor who purchased Determination of K, of WeakAcids, Catalog No. AP7949, from Flinn Scientific, Inc. and only by means of paper copies or a password-protected school website. Determination of K, of Weak Acids continuedProcedure1. Label two weighing dishes 1 and 2.2. Obtain an unknown weak acid and record the unknown letter in the Data Table.3. Measure out a small quantity (0.15-0.20 g) of the unknown into each weighing dish. Note: It is not necessary to know theexact mass of each sample.Using a graduated cylinder, precisely transfer 25.0 mL of the acid solution prepared in step 5 to an Erlenmeyer flask.Add 3 drops of phenolphthalein solution to the acid solution in the Erlenmeyer flask.Using a Beral-type pipet, add sodium hydroxide solution dropwise to the flask. Gently swirl the flask while adding thesodium hydroxide solution.Continue adding sodium hydroxide dropwise and swirling the solution until a faint pink color persists throughout the soluttion for at least 5 seconds. This is called the endpoint. Note: A pink color develops immediately when the base is added, bufades quickly once the solution is swirled. When nearing the endpoint, the pink color begins to fade more slowly. Proceedcautiously when nearing the endpoint, so as not to "overshoot" it.Using a graduated cylinder, precisely measure 50.0 ml. of distilled water into a 150-ml beaker.Transfer sample I to the water in the beaker and stir to dissolve.Note: At this point the solution in the beaker contains exactly one-half of the original amount of acid, essentially all ofwhich is in the acid form, HA. The flask contains an equal amount of the conjugate base A- obtained by neutralization.Pour the contents of the Erlenmeyer flask back into the beaker. Pour the solution back and forth a few times to mix. NotIt is important to transfer the solution as completely as possible from the flask back into the beaker.Using a pH meter, measure the pH of the resulting solution in the beaker, which contains equal molar amounts of the acand its conjugate base. Record the pH in the Data Table.Dispose of the beaker contents according to the teacher's instructions and rinse both the beaker and the Erlenmeyer flaswith distilled water. Dry the beaker with a paper towel.(7.08 ×10)²Ka=Repeat steps 4-12 using sample 2.Repeat steps 1-13 for one of the remaining unknowns.H=10-7.15a Table-7.08×10nownABC>TrialSample 1Sample 2Sample 1Sample 2Sample 1Sample 2Sample 1Sample 2Sample 1Sample 2pH70177.142.552,532015 Flinn Scientific, Inc. All Rights Reserved. No part ofal, without permission in writing inng from 1m Flinn Scientific, Inc. SpH (average)7,152.54pKthis mesbe reproduced or transmitted in anyy be shared only by the instructor who or by any means, electronic or mechani-purchased Determination ofWeakUnknown IdentityCatalog No. AP7949, from Flinn Scientific, Inc. and only by means of paper copies or a password-protected school website.Post-Laboratory Review Questions1. Average the pH readings for each trial (samples 1 and 2) to calculate the average pK, value for the unknown weakenter answers in the Data Table.2. Comment on the precision (reproducibility) of the pK, determinations. Describe sources of experimental error alikely effect on the measured pK, (pH) values.avis VI CAR ACH3. The following table lists the identities of the unknowns in this experiment. Complete the table by calculating thfor each acid. Note: pK, = -logK.AcidPotassium dihydrogen phosphatePotassium hydrogen sulfatePotassium hydrogen phthalatePotassium hydrogen tartrateAcetylsalicylic acidFormulaKH₂PO4KHSO4KK of H,PO = 6.2 × 10-8K of H₂SO4 = 1.0×10²K, of H₂CH₂O = 3.9 x 10-6K of H₂CH₂O = 4.6 × 10-²K = 3.2 × 10 +KHC HẠO.KHC_H,O.2-CH CO,C H_COOH4. Compare the experimental pK, value for each unknown with the literature values reported in question 3. Deterprobable identity of each unknown and enter the answers in the Data Table.5. Why was it not necessary to know the exact mass of each acid sample?pk5. Write separate equations for each unknown potassium salt dissolving in water and for the ionization reactionacid anion that each of these salts contains. (See Equations 7 and 8.)Why was it not necessary to know the exact concentration of the sodium hydroxide solution?Why was it necessary to measure the exact volume of distilled water used to dissolve the acid, as well as thesolution transferred from the beaker to the Erlenmeyer flask?2015 Flinn Scientific, Inc. All Rights Reserved. No part of this material may be reproduced or transmitted in any form or by any means, electrcal, without permission in writing from Flinn Scientific, Inc. Student pages may be shared only be the instr

Given: Sample pH pH (average) pKa Identity A Sample 1 7.17 7.15 7.15 Sample 2 7.14 B Sample 1 2.55 2.54 2.54 Sample 2 2.53 Acid Formula Ka pKa Potassium duhydrogen phosphate KH2PO4 Ka2 of H3PO4 = 6.2×10-8 -log(6.2×10-8)=7.2 Potassium hydrogen sulfate KSO4 Ka2 of H2SO4 = 1.0×10-2 -log(1.0×10-2)=2.0 potassium hydrogen phthlate KHC8H4O4 Ka2 of H2C8H4O4= 3.9×10-6 -log(3.9×10-6)=5.4 Potassium hydrogen tartrate KHC4H4O6 Ka2 of H2C4H4O6 = 4.6×10-5 -log(4.6×10-5)=4.34 Acetylsalicylic acid 2-CH3CO2C6H4OOH Ka = 3.2×10-4 -log(3.2×10-4)=3.5 pH of the solution is given by, pH=pKa+log[A-][HA]At end point: [A-]=[HA]pH=pKa Sample pH pH (average) pKa Identity A Sample 1 7.17 7.15 7.15 Potassium duhydrogen phosphate (KH2PO4) Sample 2 7.14 B Sample 1 2.55 2.54 2.54 Potassium hydrogen sulfate(KSO4) Sample 2 2.53